D. Bonacorsi

Our knowledge of the fundamental particles of nature and their interactions is summarized by the standard model of particle physics. Advancing our understanding in this field has required experiments that operate at ever higher energies and intensities, which produce extremely large and information-rich data samples. The use of machine-learning techniques is revolutionizing how we interpret these data samples, greatly increasing the discovery potential of present and future experiments. Here we summarize the challenges and opportunities that come with the use of machine learning at the frontiers of particle physics.

Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.

Machine learning is an important applied research area in particle physics, beginning with applications to high-level physics analysis in the 1990s and 2000s, followed by an explosion of applications in particle and event identification and reconstruction in the 2010s. In this document we discuss promising future research and development areas in machine learning in particle physics with a roadmap for their implementation, software and hardware resource requirements, collaborative initiatives with the data science community, academia and industry, and training the particle physics community in data science. The main objective of the document is to connect and motivate these areas of research and development with the physics drivers of the High-Luminosity Large Hadron Collider and future neutrino experiments and identify the resource needs for their implementation. Additionally we identify areas where collaboration with external communities will be of great benefit.

A new general purpose fixed target facility is proposed at the CERN SPS accelerator which is aimed at exploring the domain of hidden particles and make measurements with tau neutrinos. Hidden particles are predicted by a large number of models beyond the Standard Model. The high intensity of the SPS 400~GeV beam allows probing a wide variety of models containing light long-lived exotic particles with masses below ${\cal O}$(10)~GeV/c$^2$, including very weakly interacting low-energy SUSY states. The experimental programme of the proposed facility is capable of being extended in the future, e.g. to include direct searches for Dark Matter and Lepton Flavour Violation.

We report the direct observation of muon neutrino interactions with the SND@LHC detector at the Large Hadron Collider. A dataset of proton-proton collisions at sqrt[s]=13.6 TeV collected by SND@LHC in 2022 is used, corresponding to an integrated luminosity of 36.8 fb^{-1}. The search is based on information from the active electronic components of the SND@LHC detector, which covers the pseudorapidity region of 7.2<η<8.4, inaccessible to the other experiments at the collider. Muon neutrino candidates are identified through their charged-current interaction topology, with a track propagating through the entire length of the muon detector. After selection cuts, 8 ν_{μ} interaction candidate events remain with an estimated background of 0.086 events, yielding a significance of about 7 standard deviations for the observed ν_{μ} signal.

An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z0 decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B0 d mass eigenstates

The longitudinal polarization, the transverse polarization, and the forward-backward asymmetry of $\Lambda$ baryons, have been measured using a sample of 4.34 million hadronic $\mathrm{Z}^0$ decays collected with the OPAL detector at LEP between 1990 and 1995. These results are important as an aid to the understanding of hadronization mechanisms. Significant longitudinal polarization has been observed at intermediate and high momentum. For $x_E$ ( $\equiv 2 E_{\Lambda}/\sqrt{s}) >$ 0.3, the longitudinal polarization has been measured to be $-32.9 \pm 5.5 $ (stat) $\pm$ 5.2 (syst)%. We have observed no transverse polarization. A significant forward-backward asymmetry has been measured and can be described by a JETSET model.

A study of b quark hadronisation is presented using inclusively reconstructed B hadrons in about four million hadronic Z decays recorded in 1992-2000 with the OPAL detector at LEP. The data are compared to different theoretical models, and fragmentation function parameters of these models are fitted. The average scaled energy of weakly decaying B hadrons is determined to be <xe>=0.7193+-0.0016(stat)+0.0036-0.0031(syst)

Photonic events with large missing energy have been observed in $\rm e^+e^-$ collisions at a centre-of-mass energy of 189 GeV using the OPAL detector at LEP. Results are presented for event topologies consistent with a single photon or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection, and the number of light neutrino species is measured. Cross-section results are compared with the expectations from the Standard Model process $\mathrme^+\mathrme^-\to \nu\overline{\nu}$ + photon(s). No evidence is observed for new physics contributions to these final states. Upper limits on $\sigma(\mathrme^+\mathrme^-\to\mathrm{X}\mathrm{Y})\cdot\mathrm{BR}(\mathrm{X}\to\mathrm{Y}\gamma)$ and $\sigma(\mathrme^+\mathrme^-\to\mathrm{XX})\cdot\mathrm{BR}^2(\mathrm{X}\to\mathrm{Y}\gamma)$ are derived for the case of stable and invisible $\mathrm{Y}$ . These limits apply to single and pair production of excited neutrinos ( $\mathrm{X} = \nu^*, \mathrm{Y} = \nu$ ), to neutralino production ( $\mathrm{X}={{{\tilde{\chi}}^{0}}_{2}}, \mathrm{Y}={{{\tilde{\chi}}^{0}}_{1}}$ ) and to supersymmetric models in which $\mathrm{X} ={{{\tilde{\chi}}^{0}}_{1}}$ and $\mathrm{Y}={\tilde{\mathrm{G}}}$ is a light gravitino. The case of macroscopic decay lengths of particle X is considered for $\mathrme^+\mathrme^- \to \mathrm{XX}$ , $\rm X \to Y \gamma$ , when $M_{\mathrm Y}\approx 0$ . The single-photon results are also used to place upper limits on superlight gravitino pair production as well as graviton-photon production in the context of theories with additional space dimensions.

Detection of anomalous behaviors in data centers is crucial to predictive maintenance and data safety. With data centers, we mean any computer network that allows users to transmit and exchange data and information. In particular, we focus on the Tier-1 data center of the Italian Institute for Nuclear Physics (INFN), which supports the high-energy physics experiments at the Large Hadron Collider (LHC) in Geneva. The center provides resources and services needed for data processing, storage, analysis, and distribution. Log records in the data center is a stochastic and non-stationary phenomenon in nature. We propose a real-time approach to monitor and classify log records based on sliding time windows, and a time-varying evolving fuzzy-rule-based classification model. The most frequent log pattern according to a control chart is taken as the normal system status. We extract attributes from time windows to gradually develop and update an evolving Gaussian Fuzzy Classifier (eGFC) on the fly. The real-time anomaly monitoring system has to provide encouraging results in terms of accuracy, compactness, and real-time operation.

The production rates of ${\rm D}^{*\pm}$ mesons in charm and bottom events at centre-of-mass energies of about 91 GeV and the partial width of primary ${\rm c\bar c}$ pairs in hadronic ${\rm Z}^0$ decays have been measured at LEP using almost 4.4 million hadronic ${\rm Z}^0$ decays collected with the OPAL detector between 1990 and 1995. Using a combination of several charm quark tagging methods based on fully and partially reconstructed ${\rm D}^{*\pm}$ mesons, and a bottom tag based on identified muons and electrons, the hadronisation fractions of charm and bottom quarks into ${\rm D}^{*\pm}$ mesons have been found to be \[ {\rm f(b \to D^{*+}}X) = 0.173 \pm 0.016 \pm 0.012\quad {\rm and }\quad {\rm f (c \to D^{*+}}X) = 0.222 \pm 0.014 \pm 0.014\; . \] The fraction of ${\rm c\bar c}$ events in hadronic ${\rm Z}^0$ decays, $\Gamma_{\rm c\bar c}/\Gamma_{\rm had}=\Gamma({\rm Z}^0\to{\rm c\bar c}) / \Gamma({\rm Z}^0\to\rm hadrons)$ , is determined to be \[ \Gamma_{\rm c\bar c}/\Gamma_{\rm had} = 0.180\pm 0.011 \pm 0.012 \pm 0.006 \ . \] In all cases the first error is statistical, and the second one systematic. The last error quoted for $\Gamma_{\rm c\bar c}/\Gamma_{\rm had}$ is due to external branching ratios.

The process $\mathrm{e}^+\mathrm{e}^- \to\gamma\gamma(\gamma)$ is studied using data collected by the OPAL detector at LEP between the years 1997 and 2000. The data set corresponds to an integrated luminosity of 672.3 pb-1 at centre-of-mass energies lying between 181 GeV and 209 GeV. Total and differential cross-sections are determined and found to be in good agreement with the predictions of QED. Fits to the observed angular distributions are used to set limits on parameters from several models of physics beyond the Standard Model such as cut-off parameters, contact interactions of the type $\mathrm{e}^+\mathrm{e}^- \gamma\gamma$ , gravity in extra spatial dimensions and excited electrons. In events with three photons in the final state the mass spectrum of photon pairs is investigated. No narrow resonance $X\to\gamma\gamma$ is found and limits are placed on the product of the $\rm X \gamma$ production cross-section and branching ratio.

A search for the Standard Model Higgs boson has been performed with the OPAL detector at LEP based on the full data sample collected at s≈192–209 GeV in 1999 and 2000, corresponding to an integrated luminosity of approximately 426 pb−1. The data are examined for their consistency with the background-only hypothesis and various Higgs boson mass hypotheses. A lower bound of 109.7 GeV is obtained on the Higgs boson mass at the 95% confidence level. At higher masses, the data are consistent with both the background and the signal-plus-background hypotheses.

A search for single top quark production via flavour changing neutral currents (FCNC) was performed with data collected by the OPAL detector at the e+e− collider LEP. Approximately 600 pb−1 of data collected at s=189–209 GeV were used to search for the FCNC process e+e−→tc(u)→bWc(u). This analysis is sensitive to the leptonic and the hadronic decay modes of the W boson. No evidence for a FCNC process is observed. Upper limits at the 95% confidence level on the single top production cross-section as a function of the centre-of-mass energy are derived. Limits on the anomalous coupling parameters κγ and κZ are determined from these results.

A search for pair-produced doubly charged Higgs bosons has been performed using data samples corresponding to an integrated luminosity of about 614 pb−1 collected with the OPAL detector at LEP at centre-of-mass energies between 189 GeV and 209 GeV. No evidence for a signal has been observed. A mass limit of 98.5 GeV/c2 at the 95% confidence level has been set for the doubly charged Higgs particle in left–right symmetric models. This is the first search for doubly charged Higgs bosons at centre-of-mass energies larger than 91 GeV.

Using radiative Z0→ τ+τ−γevents collected with the OPAL detector at LEP at s=MZ during 1990–95, a direct study of the electromagnetic current at the τγ vertex has been performed in terms of the anomalous magnetic form factor F2 of the τ lepton. The analysis is based on a data sample of 1429 e+e−→τ+τ−γevents which are examined for a deviation from the expectation with F2=0. From the non-observation of anomalous τ+τ−γproduction a limit of−0.068<F2<0.065is obtained. This can also be interpreted as a limit on the electric dipole form factor F3 as|eF3|<3.7×10−16ecm.The above ranges are valid at the 95% confidence level.

Searches for a scalar top quark and a scalar bottom quark have been performed using a data sample of 438 pb−1 at centre-of-mass energies of s=192–209 GeV collected with the OPAL detector at LEP. No evidence for a signal was found. The 95% confidence level lower limit on the scalar top quark mass is 97.6 GeV if the mixing angle between the supersymmetric partners of the left- and right-handed states of the top quark is zero. When the scalar top quark decouples from the Z0 boson, the lower limit is 95.7 GeV. These limits were obtained assuming that the scalar top quark decays into a charm quark and the lightest neutralino, and that the mass difference between the scalar top quark and the lightest neutralino is larger than 10 GeV. The complementary decay mode of the scalar top quark decaying into a bottom quark, a charged lepton and a scalar neutrino has also been studied. The lower limit on the scalar top quark mass is 96.0 GeV for this decay mode, if the mass difference between the scalar top quark and the scalar neutrino is greater than 10 GeV and if the mixing angle of the scalar top quark is zero. From a search for the scalar bottom quark, a mass limit of 96.9 GeV was obtained if the mass difference between the scalar bottom quark and the lightest neutralino is larger than 10 GeV.

Searches for a scalar top quark and a scalar bottom quark have been performed using a data sample of 182 pb−1 at a centre-of-mass energy of s=189 GeV collected with the OPAL detector at LEP. No evidence for a signal was found. The 95% confidence level (C.L.) lower limit on the scalar top quark mass is 90.3 GeV if the mixing angle between the supersymmetric partners of the left- and right-handed states of the top quark is zero. In the worst case, when the scalar top quark decouples from the Z0 boson, the lower limit is 87.2 GeV. These limits were obtained assuming that the scalar top quark decays into a charm quark and the lightest neutralino, and that the mass difference between the scalar top quark and the lightest neutralino is larger than 10 GeV. The complementary decay mode of the scalar top quark decaying into a bottom quark, a charged lepton and a scalar neutrino has also been studied. From a search for the scalar bottom quark, a mass limit of 88.6 GeV was obtained if the mass difference between the scalar bottom quark and the lightest neutralino is larger than 7 GeV. These limits significantly improve the previous OPAL limits.

We measure the mass of the τ to be 1775.1±1.6(mcnstat.)±1.0(mcnsys.) MeV using τ from Z0 decays. To test CPT invariance we compare the masses of the positively and negatively charged τ. The relative mass difference is found to be smaller than 3.0×10−3 at the 90% confidence level.

The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element Vcb has been measured using B̄0→D∗+ℓ−ν̄ decays recorded on the Z0 peak using the OPAL detector at LEP. The D∗+→D0π+ decays were reconstructed both in the particular decay modes D0→K−π+ and D0→K−π+π0 and via an inclusive technique. The product of |Vcb| and the decay form factor of the B̄0→D∗+ℓ−ν̄ transition at zero recoil F(1) was measured to be F(1)|Vcb|=(37.1±1.0±2.0)×10−3, where the uncertainties are statistical and systematic respectively. By using Heavy Quark Effective Theory calculations for F(1), a value of|Vcb|=(40.7±1.1±2.2±1.6)×10−3was obtained, where the third error is due to theoretical uncertainties in the value of F(1). The branching ratio Br(B̄0→D∗+ℓ−ν̄) was also measured to be (5.26±0.20±0.46)%.

Searches for the neutral Higgs bosons predicted by the Standard Model (SM) and the Minimal Supersymmetric extension of the Standard Model (MSSM) have been performed with the OPAL detector at LEP. Approximately 170 pb $^{-1}$ of $\mathrm{e}^+ \mathrm{e}^-$ collision data collected at $\sqrt{s} \approx 189$ GeV were used to search for Higgs boson production in the SM process ${\mathrm{e}}^+{\mathrm{e}}^- \rightarrow \mathrm{H}^{0}\mathrm{Z}^{0}$ and the MSSM processes ${\mathrm{e}}^+{\mathrm{e}}^- \rightarrow \mathrm{h}^{0} \mathrm{Z}^{0}$ and ${\mathrm{e}}^+ {\mathrm{e}}^- \rightarrow \mathrm{A}^{0} \mathrm{h}^{0}$ . The searches are sensitive to the $\mathrm{b}\bar{\mathrm{b}}$ and $\tau^+\tau^-$ decay modes of the Higgs bosons, and also to the MSSM decay mode $\mathrm{h}^{0} \rightarrow \mathrm{A}^{0} \mathrm{A}^{0}$ . OPAL search results at lower centre-of-mass energies have been incorporated in the limits, which are valid at the 95% confidence level. For the SM Higgs boson, a lower mass bound of 91.0 GeV is obtained. In the MSSM, the limits are $m_{\mathrm{H}} >74.8$ GeV and $m_{\mathrm{A}} >76.5$ GeV, assuming $\tan\beta > 1$ , that the mixing of the scalar top quarks is either zero or maximal, and that the soft SUSY-breaking masses are 1 TeV. For the case of zero scalar top mixing, the values of $\tan\beta$ between 0.72 and 2.19 are excluded.

From a data sample of 183 pb−1 recorded at a center-of-mass energy of s=189 GeV with the OPAL detector at LEP, 3068 W-pair candidate events are selected. Assuming Standard Model W boson decay branching fractions, the W-pair production cross section is measured to be σWW=16.30±0.34(stat.)±0.18(syst.) pb. When combined with previous OPAL measurements, the W boson branching fraction to hadrons is determined to be 68.32±0.61(stat.)±0.28(syst.)% assuming lepton universality. These results are consistent with Standard Model expectations.

The CMS experiment at LHC has developed a baseline Computing Model addressing the needs of a computing system capable to operate in the first years of LHC running. It is focused on a data model with heavy streaming at the raw data level based on trigger, and on the achievement of the maximum flexibility in the use of distributed computing resources. The CMS distributed Computing Model includes a Tier-0 centre at CERN, a CMS Analysis Facility at CERN, several Tier-1 centres located at large regional computing centres, and many Tier-2 centres worldwide. The workflows have been identified, along with a baseline architecture for the data management infrastructure. This model is also being tested in Grid Service Challenges of increasing complexity, coordinated with the Worldwide LHC Computing Grid community.

The CMS experiment will need to sustain uninterrupted high reliability, high throughput and very diverse data transfer activities as the LHC operations start. PhEDEx, the CMS data transfer system, will be responsible for the full range of the transfer needs of the experiment. Covering the entire spectrum is a demanding task: from the critical high-throughput transfers between CERN and the Tier-1 centres, to high-scale production transfers among the Tier-1 and Tier-2 centres, to managing the 24/7 transfers among all the 170 institutions in CMS and to providing straightforward access to handful of files to individual physicists.

Abstract The Scattering and Neutrino Detector at the LHC (SND@LHC) started taking data at the beginning of Run 3 of the LHC. The experiment is designed to perform measurements with neutrinos produced in proton-proton collisions at the LHC in an energy range between 100 GeV and 1 TeV. It covers a previously unexplored pseudo-rapidity range of $$7.2&lt;\eta &lt;8.4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>7.2</mml:mn> <mml:mo>&lt;</mml:mo> <mml:mi>η</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mn>8.4</mml:mn> </mml:mrow> </mml:math> . The detector is located 480 m downstream of the ATLAS interaction point in the TI18 tunnel. It comprises a veto system, a target consisting of tungsten plates interleaved with nuclear emulsion and scintillating fiber (SciFi) trackers, followed by a muon detector (UpStream, US and DownStream, DS). In this article we report the measurement of the muon flux in three subdetectors: the emulsion, the SciFi trackers and the DownStream Muon detector. The muon flux per integrated luminosity through an 18 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 18 cm $$^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>2</mml:mn> </mml:msup> </mml:math> area in the emulsion is: $$\begin{aligned} 1.5 \pm 0.1(\text {stat}) \times 10^4\,\text {fb/cm}^{2}. \end{aligned}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtable> <mml:mtr> <mml:mtd> <mml:mrow> <mml:mn>1.5</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.1</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>stat</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> <mml:mspace /> <mml:msup> <mml:mtext>fb/cm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>.</mml:mo> </mml:mrow> </mml:mtd> </mml:mtr> </mml:mtable> </mml:mrow> </mml:math> The muon flux per integrated luminosity through a 31 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 31 cm $$^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>2</mml:mn> </mml:msup> </mml:math> area in the centre of the SciFi is: $$\begin{aligned} 2.06\pm 0.01(\text {stat})\pm 0.12(\text {sys}) \times 10^{4} \text {fb/cm}^{2} \end{aligned}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtable> <mml:mtr> <mml:mtd> <mml:mrow> <mml:mn>2.06</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>stat</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>±</mml:mo> <mml:mn>0.12</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>sys</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> <mml:msup> <mml:mtext>fb/cm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:mtd> </mml:mtr> </mml:mtable> </mml:mrow> </mml:math> The muon flux per integrated luminosity through a 52 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 52 cm $$^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>2</mml:mn> </mml:msup> </mml:math> area in the centre of the downstream muon system is: $$\begin{aligned} 2.35\pm 0.01(\text {stat})\pm 0.10(\text {sys}) \times 10^{4}\,\text {fb/cm}^{2} \end{aligned}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtable> <mml:mtr> <mml:mtd> <mml:mrow> <mml:mn>2.35</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>stat</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>±</mml:mo> <mml:mn>0.10</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>sys</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> <mml:mspace /> <mml:msup> <mml:mtext>fb/cm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:mtd> </mml:mtr> </mml:mtable> </mml:mrow> </mml:math> The total relative uncertainty of the measurements by the electronic detectors is 6 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> for the SciFi and 4 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> for the DS measurement. The Monte Carlo simulation prediction of these fluxes is 20–25 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> lower than the measured values.

Nowadays Machine Learning (ML) techniques are successfully used in many areas of High-Energy Physics (HEP) and will play a significant role also in the upcoming High-Luminosity LHC upgrade foreseen at CERN, when a huge amount of data will be produced by LHC and collected by the experiments, facing challenges at the exascale. To favor the usage of ML in HEP analyses, it would be useful to have a service allowing to perform the entire ML pipeline (in terms of reading the data, processing data, training a ML model, and serving predictions) directly using ROOT files of arbitrary size from local or remote distributed data sources. The Machine Learning as a Service for HEP (MLaaS4HEP) solution we have already proposed aims to provide such kind of service and to be HEP experiment agnostic. To provide users with a real service and to integrate it into the INFN Cloud, we started working on MLaaS4HEP cloudification. This would allow to use cloud resources and to work in a distributed environment. In this work, we provide updates on this topic and discuss a working prototype of the service running on INFN Cloud. It includes an OAuth2 proxy server as authentication/authorization layer, a MLaaS4HEP server, an XRootD proxy server for enabling access to remote ROOT data, and the TensorFlow as a Service (TFaaS) service in charge of the inference phase. With this architecture a HEP user can submit ML pipelines, after being authenticated and authorized, using local or remote ROOT files simply using HTTP calls.

Machine learning (ML) and deep learning (DL) techniques are increasingly influential in High Energy Physics, necessitating effective computing infrastructures and training opportunities for users and developers, particularly concerning programmable hardware like FPGAs. A gap exists in accessible ML/DL on FPGA tutorials catering to diverse hardware specifications. To bridge this gap, collaborative efforts by INFN-Bologna, the University of Bologna, and INFN-CNAF produced a pilot course using virtual machines, inhouse cloud platforms, and AWS instances, utilizing Docker containers for interactive exercises. Additionally, the Bond Machine software ecosystem, capable of generating FPGA-synthesizable computer architectures, is explored as a simplified approach for teaching FPGA programming.

New measurements are presented of the photon structure function F2γ(x,Q2) at four values of Q2 between 9 and 59 GeV2 based on data collected with the OPAL detector at centre-of-mass energies of 161–172 GeV, with a total integrated luminosity of 18.1 pb−1. The evolution of F2γ with Q2 in bins of x is determined in the Q2 range from 1.86 to 135 GeV2 using data taken at centre-of-mass energies of 91 GeV and 161–172 GeV. F2γ is observed to increase with Q2 with a slope of α−1dF2γdlnQ2 = 0.10−0.03+0.05 measured in the range 0.1 < x < 0.6.

This paper presents updated measurements of the lifetimes of the Bs0 meson and the Λb0 baryon using 4.4 million hadronic Z0 decays recorded by the OPAL detector at LEP from 1990 to 1995. A sample of Bs0 decays is obtained using Ds−ℓ+ combinations, where the Ds− is fully reconstructed in the φπ−, K∗0K− and K−K0S decay channels and partially reconstructed in the φℓ−ν̄X decay mode. A sample of Λb0 decays is obtained using Λc+ℓ− combinations, where the Λc+ is fully reconstructed in its decay to a pK−π+ final state and partially reconstructed in the Λℓ+νX decay channel. From 172±28 Ds−ℓ+ combinations attributed to Bs0 decays, the measured lifetime is τ(Bs0)=1.50+0.16−0.15±0.04ps, where the errors are statistical and systematic, respectively. From the 129±25 Λc+ℓ− combinations attributed to Λb0 decays, the measured lifetime is τ(Λb0)=1.29+0.24−0.22±0.06ps, where the errors are statistical and systematic, respectively.

Helicity density matrix elements for inclusive K∗(892)0 mesons from hadronic Z0 decays have been measured over the full range of K∗ 0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum xp values above 0.3, with the matrix element ϱ00 rising to 0.66 ± 0.11 for xp > 0.7. The values of the real part of the off-diagonal element ϱ1 - 1 are negative at large xp, with a weighted average value of −0.09 ± 0.03 for xp > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq system from the Z0 decay. All other helicity density matrix elements measured are consistent with zero over the entire xp range. The K∗ 0 fragmentation function has also been measured and the total rate determined to be 0.74 ± 0.02 ± 0.02 K∗(892)0 mesons per hadronic Z0 decay.

A search for decays of the Bc meson was performed using data collected from 1990–1995 with the OPAL detector on or near the Z0 peak at LEP. The decay channels Bc+→J/ψπ+, Bc+→J/ψa1+ and Bc+→J/ψℓ+ν were investigated, where ℓ denotes an electron or a muon. Two candidates are observed in the mode Bc+→J/ψπ+, with an estimated background of (0.63±0.20) events. The weighted mean of the masses of the two candidates is (6.32±0.06) GeV/c2, which is consistent with the predicted mass of the Bc meson. One candidate event is observed in the mode Bc+→J/ψℓ+ν, with an estimated background of (0.82±0.19) events. No candidate events are observed in the Bc+→J/ψa1+ decay mode, with an estimated background of (1.10±0.22) events. Upper bounds at the 90% confidence level are set on the production rates for these processes.

A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section, and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.

Non-commutative QED would lead to deviations from the Standard Model depending on a new energy scale ΛNC and a unique direction in space defined by two angles η and ξ. In this analysis, η is defined as the angle between the unique direction and the rotation axis of the earth. The predictions of a tree level calculation for the process e+e−→γγ are evaluated for the specific orientation of the OPAL detector and compared to the measurements. Distributions of the polar and azimuthal photon angles are used to extract limits on the energy scale ΛNC depending on the model parameter η. It is shown that the time dependence of the total cross-section could be used to determine the model parameter ξ if there were a detectable signal. This is the first experimental study of non-commutative QED at an e+e− collider.

Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4–12 GeV has been performed in the Yukawa process $\mathrme^+ \mathrme^-\rightarrow \mathrm{b}\bar{\mathrm{b}}\mathrm{A}/\mathrm{h}\rightarrow\mathrm{b} \bar{\mathrm{b}}\tau^+\tau^-$ , using the data collected by the OPAL detector at LEP between 1992 and 1995 in $\mathrme^+ \mathrme^-$ collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on $\xi^{\mathrm{A}}_d=|\tan\beta|$ and $\xi^{\mathrm{h}}_d=|\sin\alpha/\cos\beta|$ for the production of the CP-odd A and the CP-even h, respectively, where $\tan\beta$ is the ratio of the vacuum expectation values of the Higgs doublets and $\alpha$ is the mixing angle between the neutral CP-even Higgs bosons. From our data 95% C.L. upper limits are derived for $\xi^{\mathrm{A}}_d$ within the range of 8.5 to 13.6 and for $\xi^{\mathrm{h}}_d$ between 8.2 to 13.7, depending on the mass of the Higgs boson, assuming a branching fraction into $\tau^+\tau^-$ of 100%. An interpretation of the limits within a 2HDM type II model with Standard Model particle content is given. These results impose constraints on several models that have been proposed to explain the recent BNL measurement of the muon anomalous magnetic moment.

Machine learning has been applied to several problems in particle physics research, beginning with applications to high-level physics analysis in the 1990s and 2000s, followed by an explosion of applications in particle and event identification and reconstruction in the 2010s. In this document we discuss promising future research and development areas for machine learning in particle physics. We detail a roadmap for their implementation, software and hardware resource requirements, collaborative initiatives with the data science community, academia and industry, and training the particle physics community in data science. The main objective of the document is to connect and motivate these areas of research and development with the physics drivers of the High-Luminosity Large Hadron Collider and future neutrino experiments and identify the resource needs for their implementation. Additionally we identify areas where collaboration with external communities will be of great benefit.

The 40 MHz bunched muon beam set up at CERN was used in May 2003 to make a full test of the drift tubes local muon trigger. The main goal of the test was to prove that the integration of the various devices located on a muon chamber was adequately done both on the hardware and software side of the system. Furthermore the test provided complete information about the general performance of the trigger algorithms in terms of efficiency and noise. Data were collected with the default configuration of the trigger devices and with several alternative configurations at various angles of incidence of the beam. Tests on noise suppression and di-muon trigger capability were performed.

The CMS experiment at the LHC accelerator at CERN relies on its computing infrastructure to stay at the frontier of High Energy Physics, searching for new phenomena and making discoveries. Even though computing plays a significant role in physics analysis we rarely use its data to predict the system behavior itself. A basic information about computing resources, user activities and site utilization can be really useful for improving the throughput of the system and its management. In this paper, we discuss a first CMS analysis of dataset popularity based on CMS meta-data which can be used as a model for dynamic data placement and provide the foundation of data-driven approach for the CMS computing infrastructure.

The INFN-CNAF computing center, one of the Worldwide LHC Computing Grid Tier-1 sites, is serving a large set of scientific communities, in High Energy Physics and beyond.In order to increase efficiency and to remain competitive in the long run, CNAF is launching various activities aiming at implementing a global predictive maintenance solution for the site.This requires a site-wide effort in collecting, cleaning and structuring all possibly useful data coming from log files of the various Tier-1 services and systems, as a necessary step prior to designing machine learning based approaches for predictive maintenance.Among the Tier-1 services, efficient storage systems are one of the key ingredients of Tier-1 operations.CNAF uses the StoRM service as a Grid Storage Resource Manager solution: its operations are logged in a very complex manner, as the log content is deeply unstructured and hard to be exploited for analytics purposes.Despite such difficulty, the StoRM logs are a precious source of information for operators (e. g. real-time monitoring and anomaly detection), for developers (e. g. debugging, service stability, code improvements) and for site managers (service optimization, storage usage efficiency, time and money saving ways to spot and prevent unwanted behaviors).Based on previous experiences on Big Data Analytics and Machine/Deep learning in the CMS experiment, this work describes how the StoRM logs can be handled and parsed to extract the relevant information, how such log handling can be designed to work automatically, how to define and implement metrics to tag critical states of the service, how to correlate StoRM events with external services events, and ultimately how to contribute to the future CNAF-wide predictive maintenance system.Initial results in this activity are presented and discussed.Furthermore, a mention to ongoing complementary work at the CNAF center is also mentioned.

A study of W+W− events accompanied by hard photon radiation produced in e+e− collisions at LEP is presented. Events consistent with two on-shell W-bosons and an isolated photon are selected from 183 pb−1 of data recorded at s=189 GeV. From these data, 17 W+W−γ candidates are selected with photon energy greater than 10 GeV, consistent with the Standard Model expectation. These events are used to measure the e+e−→W+W−γ cross-section within a set of geometric and kinematic cuts, σ̂WWγ=136±37±8 fb, where the first error is statistical and the second systematic. The photon energy spectrum is used to set the first direct, albeit weak, limits on possible anomalous contributions to the W+W−γγ and W+W−γZ0 vertices:−0.070GeV−2<a0/Λ2<0.070GeV−2,−0.13GeV−2<ac/Λ2<0.19GeV−2,−0.61GeV−2<an/Λ2<0.57GeV−2,where Λ represents the energy scale for new physics.

Deep inelastic electron-photon scattering is studied using e+e− data collected by the OPAL detector at centre-of-mass energies s=MZ0. The photon structure function F2γ(x,Q2) is explored in a Q2 range of 1.1 to 6.6 GeV2 at lower x values than ever before. To probe this kinematic region events are selected with a beam electron scattered into one of the OPAL luminosity calorimeters at scattering angles between 27 and 55 mrad. A measurement is presented of the photon structure function F2γ(x,Q2) at 〈Q2〉 = 1.86 GeV2 and 3.76 GeV2 in five logarithmic x bins from 0.0025 to 0.2.

Measurements of the $\tau$ lepton polarization and forward-backward polarization asymmetry near the Z $^0$ resonance using the OPAL detector are described. The measurements are based on analyses of $\tau \rightarrow{\rm e} \nu_e\nu_{\tau}, \tau\rightarrow \mu\nu_{\mu}\nu_{\tau}, \tau\rightarrow \pi\nu_{\tau}, \tau \rightarrow \rho\nu_{\tau}$ and $\tau\rightarrow{\rm a}_1\nu_{\tau}$ decays from a sample of 144,810 $\rm e^+e^-\rightarrow \tau^+\tau^-$ candidates corresponding to an integrated luminosity of 151 pb $^{-1}$ . Assuming that the $\tau$ lepton decays according to V–A theory, we measure the average $\tau$ polarization near $\sqrt{s} ={\rm M}_{\mathrm{Z}}$ to be $\langle P_{\tau}\rangle= (-14.10 \pm 0.73 \pm 0.55)\%$ and the $\tau$ polarization forward-backward asymmetry to be $\rm A_{\mathrm{pol}}^{\mathrm{FB}} = (-10.55 \pm 0.76 \pm 0.25)\%$ , where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z $^0$ interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: \begin{eqnarray} {\cal A}_{\tau} & = & 0.1456 \pm 0.0076 \pm 0.0057, \nonumber {\cal A}_{\mathrm e}& = & 0.1454 \pm 0.0108 \pm 0.0036. \nonumber \end{eqnarray} These measurements are consistent with the hypothesis of lepton universality and combine to give ${\cal A}_{\ell} = 0.1455 \pm 0.0073$ . Within the context of the Standard Model this combined result corresponds to $=0.23172 \pm 0.00092$ . Combing these results with those from the other OPAL neutral current measurements yields a value of $=0.23211 \pm 0.00068$ .

The interaction of virtual photons is investigated using the reaction ${\rm e^+e^-} \rightarrow{\rm e^+e^-}$ hadrons based on data taken by the OPAL experiment at ${\rm e^+e^-}$ centre-of-mass energies $\sqrt{s_{\rm ee}}=189-209$ GeV, for $W>5$ GeV and at an average $Q^{2}$ of 17.9 GeV $^2$ . The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET, to the NLO prediction for the reaction ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$ , and to BFKL calculations. PHOJET, NLO ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$ , and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.

A search is performed for production of short-lived particles in e+e−→XY, with X→γγ and Y→ff̄, for scalar X and scalar or vector Y. Model-independent limits in the range of 25–60 femtobarns are presented on σ(e+e−→XY)×B(X→γγ)×B(Y→ff̄) for centre-of-mass energies in the range 205–207 GeV. The data from all LEP centre-of-mass energies 88–209 GeV are also interpreted in the context of fermiophobic Higgs boson models, for which a lower mass limit of 105.5 GeV is obtained for a “benchmark” fermiophobic Higgs boson.

We present measurements of triple gauge boson coupling parameters using data recorded by the OPAL detector at LEP2 at a centre-of-mass energy of 172 GeV. A total of 120 W-pair candidates has been selected in the qqqq, qq`ν` and `ν`` ′ ν`′ decay channels, for an integrated luminosity of 10.4 pb. We use these data to determine several different anomalous coupling parameters using the measured cross-section and the distributions of kinematic variables. We measure αBφ=0.35 +1.29 −1.07 ± 0.38, αWφ=0.00 +0.30 −0.28 ± 0.11, αW=0.18 +0.49 −0.47 ± 0.23, ∆g z 1=−0.03 +0.40 −0.37 ± 0.14, ∆κ γ =0.03 +0.55 −0.51± 0.20, and ∆κ=0.03 +0.49 −0.46± 0.21. Combining the αWφ result with our previous result obtained from the 161 GeV data sample we measure αWφ=−0.08 +0.28 −0.25 ± 0.10. All of these measurements are consistent with the Standard Model. (To be submitted to Zeitschrift fur Physik C.) The OPAL Collaboration K. Ackerstaff, G. Alexander, J. Allison, N. Altekamp, K.J. Anderson, S. Anderson, S. Arcelli, S. Asai, D. Axen, G. Azuelos, A.H. Ball, E. Barberio, R.J. Barlow, R. Bartoldus, J.R. Batley, S. Baumann, J. Bechtluft, C. Beeston, T. Behnke, A.N. Bell, K.W. Bell, G. Bella, S. Bentvelsen, S. Bethke, O. Biebel, A. Biguzzi, S.D. Bird, V. Blobel, I.J. Bloodworth, J.E. Bloomer, M. Bobinski, P. Bock, D. Bonacorsi, M. Boutemeur, B.T. Bouwens, S. Braibant, L. Brigliadori, R.M. Brown, H.J. Burckhart, C. Burgard, R. Burgin, P. Capiluppi, R.K. Carnegie, A.A. Carter, J.R. Carter, C.Y. Chang, D.G. Charlton, D. Chrisman, P.E.L. Clarke, I. Cohen, J.E. Conboy, O.C. Cooke, M. Cuffiani, S. Dado, C. Dallapiccola, G.M. Dallavalle, R. Davis, S. De Jong, L.A. del Pozo, K. Desch, B. Dienes, M.S. Dixit, E. do Couto e Silva, M. Doucet, E. Duchovni, G. Duckeck, I.P. Duerdoth, D. Eatough, J.E.G. Edwards, P.G. Estabrooks, H.G. Evans, M. Evans, F. Fabbri, M. Fanti, A.A. Faust, F. Fiedler, M. Fierro, H.M. Fischer, I. Fleck, R. Folman, D.G. Fong, M. Foucher, A. Furtjes, D.I. Futyan, P. Gagnon, J.W. Gary, J. Gascon, S.M. Gascon-Shotkin, N.I. Geddes, C. Geich-Gimbel, T. Geralis, G. Giacomelli, P. Giacomelli, R. Giacomelli, V. Gibson, W.R. Gibson, D.M. Gingrich, D. Glenzinski, J. Goldberg, M.J. Goodrick, W. Gorn, C. Grandi, E. Gross, J. Grunhaus, M. Gruwe, C. Hajdu, G.G. Hanson, M. Hansroul, M. Hapke, C.K. Hargrove, P.A. Hart, C. Hartmann, M. Hauschild, C.M. Hawkes, R. Hawkings, R.J. Hemingway, M. Herndon, G. Herten, R.D. Heuer, M.D. Hildreth, J.C. Hill, S.J. Hillier, P.R. Hobson, R.J. Homer, A.K. Honma, D. Horvath, K.R. Hossain, R. Howard, P. Huntemeyer, D.E. Hutchcroft, P. Igo-Kemenes, D.C. Imrie, M.R. Ingram, K. Ishii, A. Jawahery, P.W. Jeffreys, H. Jeremie, M. Jimack, A. Joly, C.R. Jones, G. Jones, M. Jones, U. Jost, P. Jovanovic, T.R. Junk, D. Karlen, V. Kartvelishvili, K. Kawagoe, T. Kawamoto, P.I. Kayal, R.K. Keeler, R.G. Kellogg, B.W. Kennedy, J. Kirk, A. Klier, S. Kluth, T. Kobayashi, M. Kobel, D.S. Koetke, T.P. Kokott, M. Kolrep, S. Komamiya, T. Kress, P. Krieger, J. von Krogh, P. Kyberd, G.D. Lafferty, R. Lahmann, W.P. Lai, D. Lanske, J. Lauber, S.R. Lautenschlager, J.G. Layter, D. Lazic, A.M. Lee, E. Lefebvre, D. Lellouch, J. Letts, L. Levinson, S.L. Lloyd, F.K. Loebinger, G.D. Long, M.J. Losty, J. Ludwig, A. Macchiolo, A. Macpherson, M. Mannelli, S. Marcellini, C. Markus, A.J. Martin, J.P. Martin, G. Martinez, T. Mashimo, P. Mattig, W.J. McDonald, J. McKenna, E.A. Mckigney, T.J. McMahon, R.A. McPherson, F. Meijers, S. Menke, F.S. Merritt, H. Mes, J. Meyer, A. Michelini, G. Mikenberg, D.J. Miller, A. Mincer, R. Mir, W. Mohr, A. Montanari, T. Mori, M. Morii, U. Muller, S. Mihara, K. Nagai, I. Nakamura, H.A. Neal, B. Nellen, R. Nisius, S.W. O’Neale, F.G. Oakham, F. Odorici, H.O. Ogren, A. Oh, N.J. Oldershaw, M.J. Oreglia, S. Orito, J. Palinkas, G. Pasztor, J.R. Pater, G.N. Patrick, J. Patt, M.J. Pearce, R. Perez-Ochoa, S. Petzold, P. Pfeifenschneider , J.E. Pilcher, J. Pinfold, D.E. Plane, P. Poffenberger, B. Poli, A. Posthaus, D.L. Rees, D. Rigby, S. Robertson, S.A. Robins, N. Rodning, J.M. Roney, A. Rooke, E. Ros, A.M. Rossi, P. Routenburg, Y. Rozen, K. Runge, O. Runolfsson, U. Ruppel, D.R. Rust, R. Rylko, K. Sachs, T. Saeki, E.K.G. Sarkisyan, C. Sbarra, A.D. Schaile, O. Schaile, F. Scharf, P. Scharff-Hansen, P. Schenk, J. Schieck, P. Schleper, B. Schmitt, S. Schmitt, A. Schoning, M. Schroder, H.C. Schultz-Coulon, M. Schumacher, C. Schwick, W.G. Scott, T.G. Shears, B.C. Shen, C.H. Shepherd-Themistocleous , 1 P. Sherwood, G.P. Siroli, A. Sittler, A. Skillman, A. Skuja, A.M. Smith, G.A. Snow, R. Sobie, S. Soldner-Rembold, R.W. Springer, M. Sproston, K. Stephens, J. Steuerer, B. Stockhausen, K. Stoll, D. Strom, P. Szymanski, R. Tafirout, S.D. Talbot, S. Tanaka, P. Taras, S. Tarem, R. Teuscher, M. Thiergen, M.A. Thomson, E. von Torne, S. Towers, I. Trigger, Z. Trocsanyi, E. Tsur, A.S. Turcot, M.F. Turner-Watson, P. Utzat, R. Van Kooten, M. Verzocchi, P. Vikas, E.H. Vokurka, H. Voss, F. Wackerle, A. Wagner, C.P. Ward, D.R. Ward, P.M. Watkins, A.T. Watson, N.K. Watson, P.S. Wells, N. Wermes, J.S. White, B. Wilkens, G.W. Wilson, J.A. Wilson, G. Wolf, T.R. Wyatt, S. Yamashita, G. Yekutieli, V. Zacek, D. Zer-Zion School of Physics and Space Research, University of Birmingham, Birmingham B15 2TT, UK Dipartimento di Fisica dell’ Universita di Bologna and INFN, I-40126 Bologna, Italy Physikalisches Institut, Universitat Bonn, D-53115 Bonn, Germany Department of Physics, University of California, Riverside CA 92521, USA Cavendish Laboratory, Cambridge CB3 0HE, UK 6 Ottawa-Carleton Institute for Physics, Department of Physics, Carleton University, Ottawa, Ontario K1S 5B6, Canada Centre for Research in Particle Physics, Carleton University, Ottawa, Ontario K1S 5B6, Canada CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago IL 60637, USA Fakultat fur Physik, Albert Ludwigs Universitat, D-79104 Freiburg, Germany Physikalisches Institut, Universitat Heidelberg, D-69120 Heidelberg, Germany Indiana University, Department of Physics, Swain Hall West 117, Bloomington IN 47405, USA Queen Mary and Westfield College, University of London, London E1 4NS, UK Technische Hochschule Aachen, III Physikalisches Institut, Sommerfeldstrasse 26-28, D-52056 Aachen, Germany University College London, London WC1E 6BT, UK Department of Physics, Schuster Laboratory, The University, Manchester M13 9PL, UK Department of Physics, University of Maryland, College Park, MD 20742, USA Laboratoire de Physique Nucleaire, Universite de Montreal, Montreal, Quebec H3C 3J7, Canada University of Oregon, Department of Physics, Eugene OR 97403, USA Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel Department of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel International Centre for Elementary Particle Physics and Department of Physics, University of Tokyo, Tokyo 113, and Kobe University, Kobe 657, Japan Brunel University, Uxbridge, Middlesex UB8 3PH, UK Particle Physics Department, Weizmann Institute of Science, Rehovot 76100, Israel Universitat Hamburg/DESY, II Institut fur Experimental Physik, Notkestrasse 85, D-22607 Hamburg, Germany University of Victoria, Department of Physics, P O Box 3055, Victoria BC V8W 3P6, Canada University of British Columbia, Department of Physics, Vancouver BC V6T 1Z1, Canada 2 University of Alberta, Department of Physics, Edmonton AB T6G 2J1, Canada Duke University, Dept of Physics, Durham, NC 27708-0305, USA Research Institute for Particle and Nuclear Physics, H-1525 Budapest, P O Box 49, Hungary Institute of Nuclear Research, H-4001 Debrecen, P O Box 51, Hungary Ludwigs-Maximilians-Universitat Munchen, Sektion Physik, Am Coulombwall 1, D-85748 Garching, Germany a and at TRIUMF, Vancouver, Canada V6T 2A3 b and Royal Society University Research Fellow c and Institute of Nuclear Research, Debrecen, Hungary d and Department of Experimental Physics, Lajos Kossuth University, Debrecen, Hungary e and Department of Physics, New York University, NY 1003, USA

Artificial Intelligence (AI) techniques have been implemented in the field of Medical Imaging for more than forty years.Medical Physicists, Clinicians and Computer Scientists have been collaborating since the beginning to realize software solutions to enhance the informative content of medical images, including AI-based support systems for image interpretation.Despite the recent massive progress in this field due to the current emphasis on Radiomics, Machine Learning and Deep Learning, there are still some barriers to overcome before these tools are fully integrated into the clinical workflows to finally enable a precision medicine approach to patients' care.Nowadays, as Medical Imaging has entered the Big Data era, innovative solutions to efficiently deal with huge amounts of data and to exploit large and distributed computing resources are urgently needed.In the framework of a collaboration agreement between the Italian Association of Medical Physicists (AIFM) and the National Institute for Nuclear Physics (INFN), we propose a model of an intensive computing infrastructure, especially suited for training AI models, equipped with secure storage systems, compliant with data protection regulation, which will accelerate the development and extensive validation of AI-based solutions in the Medical Imaging field of research.This solution can be developed and made operational by Physicists and Computer Scientists working on complementary fields of research in Physics, such as High Energy Physics and Medical Physics, who have all the necessary skills to tailor the AI-technology to the needs of the Medical Imaging community and to shorten the pathway towards the clinical applicability of AI-based decision support systems.

In the Standard Model, b quarks produced in e+e− annihilation at the Z0 peak have a large average longitudinal polarization of −0.94. Some fraction of this polarization is expected to be transferred to b-flavored baryons during hadronization. The average longitudinal polarization of weakly decaying b baryons, 〈PLΛb〉, is measured in approximately 4.3 million hadronic Z0 decays collected with the OPAL detector between 1990 and 1995 at LEP. Those b baryons that decay semileptonically and produce a Λ baryon are identified through the correlation of the baryon number of the Λ and the electric charge of the lepton. In this semileptonic decay, the ratio of the neutrino energy to the lepton energy is a sensitive polarization observable. The neutrino energy is estimated using missing energy measurements. From a fit to the distribution of this ratio, the value 〈PLΛb〉=−0.56+0.20−0.13±0.09 is obtained, where the first error is statistical and the second systematic.

A search for stable and long-lived massive particles of electric charge |Q/e|=1 or 2/3, pair-produced in e+e− collisions at centre-of-mass energies from 130 to 183 GeV, is reported by the OPAL collaboration at LEP. No evidence for production of these particles was observed in a mass range between 45 and 89.5 GeV. Model-independent upper limits on the production cross-section between 0.05 and 0.19 pb have been derived for scalar and spin-1/2 particles with charge ±1. Within the framework of the minimal supersymmetric model (MSSM), this implies a lower limit of 82.5 (83.5) GeV on the mass of long-lived right- (left-)handed scalar muons and scalar taus. Long-lived charged leptons and charginos are excluded for masses below 89.5 GeV. For particles with charge ±2/3 the upper limits on the production cross-section vary between 0.05 and 0.2 pb. All limits, on masses and on cross-sections, are valid at the 95% confidence level for particles with lifetimes longer than 10−6 s.

Using about 3.9 million hadronic Z decays from e+e− collisions recorded by the OPAL detector at LEP at centre-of-mass energies s≈MZ, the branching ratio for the decay D−s→τ−ν̄τ has been measured to be BR(D−s→τ−ν̄τ)=(7.0±2.1(stat)±2.0(syst))%. This result can be used to derive the decay constant of the D−s meson: fDs=(286±44(stat)±41(syst))MeV.

The CMS experiment expects to manage several Pbytes of data each year during the LHC programme, distributing them over many computing sites around the world and enabling data access at those centers for analysis. CMS has identified the distributed sites as the primary location for physics analysis to support a wide community with thousands potential users. This represents an unprecedented experimental challenge in terms of the scale of distributed computing resources and number of user. An overview of the computing architecture, the software tools and the distributed infrastructure is reported. Summaries of the experience in establishing efficient and scalable operations to get prepared for CMS distributed analysis are presented, followed by the user experience in their current analysis activities.

The distributed Grid infrastructure for High Energy Physics experiments at the Large Hadron Collider (LHC) in Geneva comprises a set of computing centres, spread all over the world, as part of the Worldwide LHC Computing Grid (WLCG). In Italy, the Tier-1 functionalities are served by the INFN-CNAF data center, which provides also computing and storage resources to more than twenty non-LHC experiments. For this reason, a high amount of logs are collected each day from various sources, which are highly heterogeneous and difficult to harmonize. In this contribution, a working implementation of a system that collects, parses and displays the log information from CNAF data sources and the investigation of a Machine Learning based predictive maintenance system, is presented.

We search for lepton flavour violating events (eμ, eτ and μτ) that could be directly produced in e+e− annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV and 209 GeV. In general, the Standard Model expectations describe the data well for all the channels and at each s. A single eμ event is observed where according to our Monte Carlo simulations only 0.019 events are expected from Standard Model processes. We obtain the first limits on the cross-sections σ(e+e−→eμ, eτ and μτ) as a function of s at LEP2 energies.

A search for charged excited leptons decaying into a lepton and photon has been performed using approximately 680 pb-1 of e+e- collision data collected by the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV. No evidence for their existence was found. Upper limits on the product of the cross-section and the branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

The hadronic structure function of the photon F2γ(x,Q2) is measured as a function of Bjorken x and of the photon virtuality Q2 using deep-inelastic scattering data taken by the OPAL detector at LEP at e+e− centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F2γ are extended to an average Q2 of 〈Q2〉=780 GeV2 using data in the kinematic range 0.15<x<0.98. The Q2 evolution of F2γ is studied for 12.1<〈Q2〉<780 GeV2 using three ranges of x. As predicted by QCD, the data show positive scaling violations in F2γ with F2γ(Q2)/α=(0.08±0.02+0.05−0.03)+(0.13±0.01+0.01−0.01)lnQ2, where Q2 is in GeV2, for the central x region 0.10–0.60. Several parameterisations of F2γ are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data.

Using a data sample of 57 pb−1 recorded at a centre-of-mass energy of 183 GeV with the OPAL detector at LEP, 282 W+W−→qqqq and 300 W+W−→qqℓνℓ candidate events are used to obtain a measurement of the mass of the W boson, MW=80.39±0.13(stat.)±0.05(syst.) GeV, assuming the Standard Model relation between MW and ΓW. A second fit provides a direct measure of the width of the W boson and gives ΓW=1.96±0.34(stat.)±0.20(syst.) GeV. These results are combined with previous OPAL results to obtain MW=80.38±0.12(stat.)±0.05(syst.) GeV and ΓW=1.84±0.32(stat.)±0.20(syst.) GeV.

A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pb $^{-1}$ . After combining with our previous measurements at centre-of-mass energies of 161–183 GeV we obtain $\kappa=0.97_{-0.16}^{+0.20}$ , $g^{\mathrm{z}}_1=0.991^{+0.060}_{-0.057}$ and $\lambda=-0.110_{-0.055}^{+0.058}$ , where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their Standard Model values. These results are consistent with the Standard Model expectations.

Correlations among hadrons with the same electric charge produced in Z0 decays are studied using the high statistics data collected from 1991 through 1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth order are used to measure genuine particle correlations as a function of the size of phase space domains in rapidity, azimuthal angle and transverse momentum. Both all-charge and like-sign particle combinations show strong positive genuine correlations. One-dimensional cumulants initially increase rapidly with decreasing size of the phase space cells but saturate quickly. In contrast, cumulants in two- and three-dimensional domains continue to increase. The strong rise of the cumulants for all-charge multiplets is increasingly driven by that of like-sign multiplets. This points to the likely influence of Bose–Einstein correlations. Some of the recently proposed algorithms to simulate Bose–Einstein effects, implemented in the Monte Carlo model Pythia, are found to reproduce reasonably well the measured second- and higher-order correlations between particles with the same charge as well as those in all-charge particle multiplets.

The magnitude of the CKM matrix element Vub is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on b -> Xu l nu event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. We measure Br(b -> Xu l) to be (1.63 +/- 0.53 +0.55/-0.62) x 10^(-3). The first uncertainty is the statistical error and the second is the systematic error. From this analysis, Vub is determined to be: |Vub| = (4.00 +/- 0.65(stat) +0.67/-0.76(sys) +/- 0.19(HQE)) x 10^(-3). The last error represents the theoretical uncertainties related to the extraction of |Vub| from Br(b -> Xu l) using the Heavy Quark Expansion.

The mass and width of the W boson are determined in e+e− collisions at LEP using 183 pb−1 of data recorded at a centre-of-mass energy s=189 GeV with the OPAL detector. The invariant mass distributions from 970 W+W−→qqqq and 1118 W+W−→qqℓνℓ candidate events are used to measure the mass of the W boson, MW=80.451±0.076 (stat.)±0.049 (syst.) GeV. A direct measurement of the width of the W boson gives ΓW=2.09±0.18 (stat.)±0.09 (syst.) GeV. The results are combined with previous OPAL results from 78 pb−1 of data recorded with s from 161 to 183 GeV, to obtain: MW=80.432±0.066 (stat.)±0.045 (syst.) GeV, ΓW=2.04±0.16 (stat.)±0.09 (syst.) GeV. The consistency of the direct measurement of MW with that inferred from other measurements of electroweak parameters provides an important test of the Standard Model of electroweak interactions.

Searches for first generation scalar and vector leptoquarks, and for squarks in R-parity violating SUSY models with the direct decay of the squark into Standard Model particles, have been performed using e+e− collisions collected with the OPAL detector at LEP at e+e− centre-of-mass energies between 189 and 209 GeV. No excess of events is found over the expectation from Standard Model background processes. Limits are computed on the leptoquark couplings for different values of the branching ratio to electron–quark final states.

The CERN IT provides a set of Hadoop clusters featuring more than 5 PBytes of raw storage with different open-source, user-level tools available for analytical purposes. The CMS experiment started collecting a large set of computing meta-data, e.g. dataset, file access logs, since 2015. These records represent a valuable, yet scarcely investigated, set of information that needs to be cleaned, categorized and analyzed. CMS can use this information to discover useful patterns and enhance the overall efficiency of the distributed data, improve CPU and site utilization as well as tasks completion time. Here we present evaluation of Apache Spark platform for CMS needs. We discuss two main use-cases CMS analytics and ML studies where efficient process billions of records stored on HDFS plays an important role. We demonstrate that both Scala and Python (PySpark) APIs can be successfully used to execute extremely I/O intensive queries and provide valuable data insight from collected meta-data.

During the first run, CMS collected and processed more than 10B data events and simulated more than 15B events. Up to 100k processor cores were used simultaneously and 100PB of storage was managed. Each month petabytes of data were moved and hundreds of users accessed data samples. In this document we discuss the operational experience from this first run. We present the workflows and data flows that were executed, and we discuss the tools and services developed, and the operations and shift models used to sustain the system. Many techniques were followed from the original computing planning, but some were reactions to difficulties and opportunities. We also address the lessons learned from an operational perspective, and how this is shaping our thoughts for 2015.

Log-based predictive maintenance of computing centers is a main concern regarding the worldwide computing grid that supports the CERN (European Organization for Nu-clear Research) physics experiments. A log, as event-oriented ad-hoc information, is quite often given as unstructured big data. Log data processing is a time-consuming computational task. The goal is to grab essential information from a continuously changeable grid environment to construct a classification model. Evolving granular classifiers are suited to learn from time-varying log streams and, therefore, perform online classification of the severity of anomalies. We formulated a 4-class online anomaly classification problem, and employed time windows between landmarks and two granular computing methods, namely, Fuzzy-set-Based evolving Modeling (FBeM) and evolving Granular Neural Network (eGNN), to model and monitor logging activity rate. The results of classification are of utmost importance for predictive maintenance because priority can be given to specific time intervals in which the classifier indicates the existence of high or medium severity anomalies.

In the near future, large scientific collaborations will face unprecedented computing challenges. Processing and storing exabyte datasets require a federated infrastructure of distributed computing resources. The current systems have proven to be mature and capable of meeting the experiment goals, by allowing timely delivery of scientific results. However, a substantial amount of interventions from software developers, shifters and operational teams is needed to efficiently manage such heterogeneous infrastructures. A wealth of operational data can be exploited to increase the level of automation in computing operations by using adequate techniques, such as machine learning (ML), tailored to solve specific problems. The Operational Intelligence project is a joint effort from various WLCG communities aimed at increasing the level of automation in computing operations. We discuss how state-of-the-art technologies can be used to build general solutions to common problems and to reduce the operational cost of the experiment computing infrastructure.

The branching ratio for the decay τ−→e−ν̄eντ has been measured using Z0 decay data collected by the OPAL experiment at LEP. In total 33073 τ−→e−ν̄eντ candidates were identified from a sample of 186197 selected τ decays, giving a branching ratio of B(τ−→e−ν̄eντ)=(17.81±0.09(stat)±0.06(syst))%. This result is combined with other measurements to test e - μ and μ - τ universality in charged-current weak interactions. Additionally, the strong coupling constant αs(mτ2) has been extracted from B(τ−→e−ν̄eντ) and evolved to the Z0 mass scale, giving αs(mZ2)=0.1204±0.0011 (exp)±0.0019 (theory).

The lifetime and oscillation frequency of the B0 meson has been measured using B̄0→D∗+ℓ−ν̄ decays recorded on the Z0 peak with the OPAL detector at LEP. The D∗+→D0π+ decays were reconstructed using an inclusive technique and the production flavour of the B0 mesons was determined using a combination of tags from the rest of the event. The results τB0=1.541±0.028±0.023ps,Δmd=0.497±0.024±0.025ps−1 were obtained, where in each case the first error is statistical and the second is systematic.

A search for the decay B±→K±K±π∓ was performed using data collected by the OPAL detector at LEP. These decays are strongly suppressed in the Standard Model but could occur with a higher branching ratio in supersymmetric models, especially in those with R-parity violating couplings. No evidence for a signal was observed and a 90% confidence level upper limit of 1.29×10−4 was set for the branching ratio.

The rates are measured per hadronic $\mathrm{Z}^0$ decay for gluon splitting to $\mathrm{b\overline{b}}$ quark pairs, $g_{\mathrm{b\overline{b}}}$ , and of events containing two $\mathrm{b\overline{b}}$ quark pairs, $g_{\mathrm{4b}}$ , using a sample of four-jet events selected from data collected with the OPAL detector. Events with an enhanced signal of gluon splitting to $\mathrm{b\overline{b}}$ quarks are selected if two of the jets are close in phase-space and contain detached secondary vertices. For the event sample containing two $\mathrm{b\overline{b}}$ quark pairs, three of the four jets are required to have a significantly detached secondary vertex. Information from the event topology is combined in a likelihood fit to extract the values of $g_{\mathrm{b\overline{b}}}$ and $g_{\mathrm{4b}}$ , namely \begin{eqnarray*} g_{\mathrm{b\overline{b}}} & = & (3.07 \pm 0.53 \mathrm{(stat)} \pm 0.97\mathrm{(syst)})\times 10^{-3},\\ g_{\mathrm{4b}} & = & (0.36\pm 0.17 \mathrm{(stat)} \pm 0.27\mathrm{(syst)})\times 10^{-3}. \end{eqnarray*}

The charged particle multiplicities of two- and three-jet events from the reaction e $^+$ e $^-$ $\rightarrow$ Z $^0\rightarrow hadrons$ are measured for Z $^0$ decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from $\Upsilon$ and Z $^0$ decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio $r\equiv\mathrm{N}_{g}/\mathrm{N}_{q}$ of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, $r^{(1)}\equiv(\mathrm{d}\mathrm{N}_{g} /\mathrm{d}y) /(\mathrm{d}\mathrm{N}_{q} /\mathrm{d}y)$ , and of curvatures, $r^{(2)}\equiv(\mathrm{d}^2\mathrm{N}_{g} /\mathrm{d}y^2) /(\mathrm{d}^2\mathrm{N}_{q} /\mathrm{d}y^2)$ , where y specifies the energy scale. At 30 GeV, we find $r=1.422\pm0.051,r^{(1)}=1.761\pm0.071$ and $r^{(2)}=1.98\pm0.13$ , where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of ${\mathrm{N}}_{g}$ and ${\mathrm{N}}_{q}$ to determine an effective value of the ratio of QCD color factors, $C_{\mathrm A}/C_{\mathrm F}$ . Our result, $C_{\mathrm A}/C_{\mathrm F}=2.23\pm0.14 $ (total), is consistent with the QCD value of 2.25.

The τ−→μ−ν̄μντ branching ratio has been measured using data collected from 1990 to 1995 by the OPAL detector at the LEP collider. The resulting value of B(τ−→μ−ν̄μντ)=0.1734±0.0009(stat)±0.0006(syst) has been used in conjunction with other OPAL measurements to test lepton universality, yielding the coupling constant ratios gμ/ge=1.0005±0.0044 and gτ/ge=1.0031±0.0048, in good agreement with the Standard Model prediction of unity. A value for the Michel parameter η=0.004±0.037 has also been determined and used to find a limit for the mass of the charged Higgs boson, mH±>1.28tanβ, in the Minimal Supersymmetric Standard Model.

CMS computing needs reliable, stable and fast connections among multi-tiered distributed infrastructures. CMS experiment relies on File Transfer Services (FTS) for data distribution, a low level data movement service responsible for moving sets of files from one site to another, while allowing participating sites to control the network resource usage. FTS servers are provided by Tier-0 and Tier-1 centers and used by all the computing sites in CMS, subject to established CMS and sites setup policies, including all the virtual organizations making use of the Grid resources at the site, and properly dimensioned to satisfy all the requirements for them. Managing the service efficiently needs good knowledge of the CMS needs for all kind of transfer routes, and the sharing and interference with other VOs using the same FTS transfer managers. This contribution deals with a complete revision of all FTS servers used by CMS, customizing the topologies and improving their setup in order to keep CMS transferring data to the desired levels, as well as performance studies for all kind of transfer routes, including overheads measurements introduced by SRM servers and storage systems, FTS server misconfigurations and identification of congested channels, historical transfer throughputs per stream, file-latency studies,... This information is retrieved directly from the FTS servers through the FTS Monitor webpages and conveniently archived for further analysis. The project provides an interface for all these values, to ease the analysis of the data.

CMS experiment utilizes distributed computing infrastructure and its performance heavily depends on the fast and smooth distribution of data between different CMS sites. Data must be transferred from the Tier-0 (CERN) to the Tier-1s for processing, storing and archiving, and time and good quality are vital to avoid overflowing CERN storage buffers. At the same time, processed data has to be distributed from Tier-1 sites to all Tier-2 sites for physics analysis while Monte Carlo simulations sent back to Tier-1 sites for further archival. At the core of all transferring machinery is PhEDEx (Physics Experiment Data Export) data transfer system. It is very important to ensure reliable operation of the system, and the operational tasks comprise monitoring and debugging all transfer issues. Based on transfer quality information Site Readiness tool is used to create plans for resources utilization in the future. We review the operational procedures created to enforce reliable data delivery to CMS distributed sites all over the world. Additionally, we need to keep data and meta-data consistent at all sites and both on disk and on tape. In this presentation, we describe the principles and actions taken to keep data consistent on sites storage systems and central CMS Data Replication Database (TMDB/DBS) while ensuring fast and reliable data samples delivery of hundreds of terabytes to the entire CMS physics community.

During the LHC Run-1 data taking, all experiments collected large data volumes from proton-proton and heavy-ion collisions. The collisions data, together with massive volumes of simulated data, were replicated in multiple copies, transferred among various Tier levels, transformed/slimmed in format/content. These data were then accessed (both locally and remotely) by large groups of distributed analysis communities exploiting the WorldWide LHC Computing Grid infrastructure and services. While efficient data placement strategies - together with optimal data redistribution and deletions on demand - have become the core of static versus dynamic data management projects, little effort has so far been invested in understanding the detailed data-access patterns which surfaced in Run-1. These patterns, if understood, can be used as input to simulation of computing models at the LHC, to optimise existing systems by tuning their behaviour, and to explore next-generation CPU/storage/network co-scheduling solutions. This is of great importance, given that the scale of the computing problem will increase far faster than the resources available to the experiments, for Run-2 and beyond. Studying data-access patterns involves the validation of the quality of the monitoring data collected on the "popularity of each dataset, the analysis of the frequency and pattern of accesses to different datasets by analysis end-users, the exploration of different views of the popularity data (by physics activity, by region, by data type), the study of the evolution of Run-1 data exploitation over time, the evaluation of the impact of different data placement and distribution choices on the available network and storage resources and their impact on the computing operations. This work presents some insights from studies on the popularity data from the CMS experiment. We present the properties of a range of physics analysis activities as seen by the data popularity, and make recommendations for how to tune the initial distribution of data in anticipation of how it will be used in Run-2 and beyond.

Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.

The process e+e−→γγ(γ) is studied using data recorded with the OPAL detector at LEP. The data sample taken at a centre-of-mass energy of 189 GeV corresponds to a total integrated luminosity of 178 pb−1. The measured cross-section agrees well with the expectation from QED. A fit to the angular distribution is used to obtain improved limits at 95% CL on the QED cut-off parameters: Λ+> 304 GeV and Λ−> 295 GeV as well as a mass limit for an excited electron, Me∗> 306 GeV assuming equal e∗eγ and eeγ couplings. Graviton exchange in the context of theories with higher dimensions is excluded for scales G+< 660 GeV and G−< 634 GeV. No evidence for resonance production is found in the invariant mass spectrum of photon pairs. Limits are obtained for the cross-section times branching ratio for a resonance decaying into two photons and produced in association with another photon.

A search is described for the generic process e+e−→XY, where X is a neutral heavy scalar boson decaying into a pair of photons, and Y is a neutral heavy boson (scalar or vector) decaying into a fermion pair. The search is motivated mainly by the cases where either X, or both X and Y, are Higgs bosons. In particular, we investigate the case where X is the Standard Model Higgs boson and Y the Z0 boson. Other models with enhanced Higgs boson decay couplings to photon pairs are also considered. The present search combines the data set collected by the OPAL collaboration at 189 GeV collider energy, having an integrated luminosity of 182.6 pb−1, with data samples collected at lower energies. The search results have been used to put 95% confidence level bounds, as functions of the mass MX, on the product of the cross-section and the relevant branching ratios, both in a model independent manner and for the particular models considered.

The predicted effects of final state interactions such as colour reconnection are investigated by measuring properties of hadronic decays of W bosons, recorded at a centre-of-mass energy of s≃182.7 GeV in the OPAL detector at LEP. Dependence on the modelling of hadronic W decays is avoided by comparing W+W−→qq′qq′ events with the non-leptonic component of W+W−→qq′ℓνℓ events. The scaled momentum distribution, its mean value, 〈xp〉, and that of the charged particle multiplicity, 〈nch〉, are measured and found to be consistent in the two channels. The measured differences are:Δ〈nch〉=〈nch4q〉−2〈nchqqℓν〉=+0.7±0.8±0.6Δ〈xp〉=〈xp4q〉−〈xpqqℓν〉=(−0.09±0.09±0.05)×10−2.In addition, measurements of rapidity and thrust are performed for W+W−→qq′qq′ events. The data are described well by standard QCD models and disfavour one model of colour reconnection within the ARIADNE program. The current implementation of the Ellis-Geiger model of colour reconnection is excluded. At the current level of statistical precision no evidence for colour reconnection effects was found in the observables studied. The predicted effect of colour reconnection on OPAL measurements of MW is also quantified in the context of models studied.

A study of Z boson pair production in e+e− annihilation at center-of-mass energies near 183 GeV and 189 GeV is reported. Final states containing only leptons, (ℓ+ℓ−ℓ+ℓ− and ℓ+ℓ−νν), quark and lepton pairs, (qqℓ+ℓ−, qqνν) and the all-hadronic final state (qqqq) are considered. In all states with at least one Z boson decaying hadronically, qq and bb final states are considered separately using lifetime and event-shape tags, thereby improving the cross-section measurement. At s=189 GeV the Z-pair cross section was measured to be 0.80+0.14−0.13(stat.)+0.06−0.05(syst.)pb, consistent with the Standard Model prediction. At s=183 GeV the 95% C.L. upper limit is 0.55pb. Limits on anomalous ZZγ and ZZZ couplings are derived.

The inclusive branching ratio for the process b→τ−ν̄τX has been measured using hadronic Z decays collected by the OPAL experiment at LEP in the years 1992–2000. The result is: BR(b→τ−ν̄τX)=(2.78±0.18±0.51)%. This measurement is consistent with the Standard Model expectation and puts a constraint of tanβ/MH±<0.53 GeV−1 at the 95% confidence level on Type II Two Higgs Doublet Models.

The production of charm quarks is studied in deep-inelastic electron–photon scattering using data recorded by the OPAL detector at LEP at nominal e+e− centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D★ mesons using their decays into D0π with the D0 observed in two decay modes with charged particle final states, Kπ and Kπππ. The cross-section σD★ for production of charged D★ in the reaction e+e−→e+e−D★X is measured in a restricted kinematical region using two bins in Bjorken x, 0.0014<x<0.1 and 0.1<x<0.87. From σD★ the charm production cross-section σ(e+e−→e+e−cc̄X) and the charm structure function of the photon F2,cγ are determined in the region 0.0014<x<0.87 and 5<Q2<100 GeV2 . For x>0.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x<0.1 the measured cross-section is 43.8±14.3±6.3±2.8 pb with a next-to-leading order prediction of 17.0+2.9−2.3 pb.

We observe Bose–Einstein correlations in π0 pairs using back-to-back two jet hadronic events from Z0 decays in the data sample collected by the OPAL detector at LEP 1 from 1991 to 1995. Using a static Gaussian picture for the pion emitter source, we obtain the chaoticity parameter λ=0.55±0.10±0.10 and the source radius R=(0.59±0.08±0.05) fm. According to the JETSET and HERWIG Monte Carlo models, the Bose–Einstein correlations in our data sample largely connect π0s originating from the decays of different hadrons. Prompt pions formed at string break-ups or cluster decays only form a small fraction of the sample.

A novel method of determining the mass of the W boson in the ${\rm W^+ W^-} \to \ell \nu \ell^\prime \nu^\prime$ channel is presented and applied to 667 pb-1 of data recorded at center-of-mass energies in the range 183-207 GeV with the OPAL detector at LEP. The measured energies of charged leptons and the results of a new procedure based on an approximate kinematic reconstruction of the events are combined to give: M_W = 80.41\pm 0.41\pm 0.13 GeV, where the first error is statistical and the second is systematic. The systematic error is dominated by the uncertainty on the lepton energy, which is calibrated using data, and the parameterization of the variables used in the fitting, which is obtained using Monte Carlo events. Both of these are limited by statistics.

The CMS experiment is currently developing a computing system capable of serving, processing and archiving the large number of events that will be generated when the CMS detector starts taking data. During 2004 CMS undertook a large scale data challenge to demonstrate the ability of the CMS computing system to cope with a sustained data-taking rate equivalent to 25% of startup rate. Its goals were: to run CMS event reconstruction at CERN for a sustained period at 25 Hz input rate; to distribute the data to several regional centers; and enable data access at those centers for analysis. Grid middleware was utilized to help complete all aspects of the challenge. To continue to provide scalable access from anywhere in the world to the data, CMS is developing a layer of software that uses Grid tools to gain access to data and resources, and that aims to provide physicists with a user friendly interface for submitting their analysis jobs. This paper describes the data challenge experience with Grid infrastructure and the current development of the CMS analysis system.

The CMS CERN Analysis Facility (CAF) was primarily designed to host a large variety of latency-critical workflows. These break down into alignment and calibration, detector commissioning and diagnosis, and high-interest physics analysis requiring fast-turnaround. In addition to the low latency requirement on the batch farm, another mandatory condition is the efficient access to the RAW detector data stored at the CERN Tier-0 facility. The CMS CAF also foresees resources for interactive login by a large number of CMS collaborators located at CERN, as an entry point for their day-by-day analysis. These resources will run on a separate partition in order to protect the high-priority use-cases described above. While the CMS CAF represents only a modest fraction of the overall CMS resources on the WLCG GRID, an appropriately sized user-support service needs to be provided. We will describe the building, commissioning and operation of the CMS CAF during the year 2008. The facility was heavily and routinely used by almost 250 users during multiple commissioning and data challenge periods. It reached a CPU capacity of 1.4MSI2K and a disk capacity at the Peta byte scale. In particular, we will focus on the performances in terms of networking, disk access and job efficiency and extrapolate prospects for the upcoming LHC first year data taking. We will also present the experience gained and the limitations observed in operating such a large facility, in which well controlled workflows are combined with more chaotic type analysis by a large number of physicists.

The CMS experiment at CERN is preparing for LHC data taking in several computing preparation activities. In early 2007 a traffic load generator infrastructure for distributed data transfer tests was designed and deployed to equip the WLCG tiers which support the CMS virtual organization with a means for debugging, load-testing and commissioning data transfer routes among CMS computing centres. The LoadTest is based upon PhEDEx as a reliable, scalable data set replication system. The Debugging Data Transfers (DDT) task force was created to coordinate the debugging of the data transfer links. The task force aimed to commission most crucial transfer routes among CMS tiers by designing and enforcing a clear procedure to debug problematic links. Such procedure aimed to move a link from a debugging phase in a separate and independent environment to a production environment when a set of agreed conditions are achieved for that link. The goal was to deliver one by one working transfer routes to the CMS data operations team. The preparation, activities and experience of the DDT task force within the CMS experiment are discussed. Common technical problems and challenges encountered during the lifetime of the taskforce in debugging data transfer links in CMS are explained and summarized.

After a successful first run at the LHC, and during the Long Shutdown (LS1) of the accelerator, the workload and data management sectors of the CMS Computing Model are entering into an operational review phase in order to concretely assess area of possible improvements and paths to exploit new promising technology trends. In particular, since the preparation activities for the LHC start, the Networks have constantly been of paramount importance for the execution of CMS workflows, exceeding the original expectations - as from the MONARC model - in terms of performance, stability and reliability. The low-latency transfers of PetaBytes of CMS data among dozens of WLCG Tiers worldwide using the PhEDEx dataset replication system is an example of the importance of reliable Networks. Another example is the exploitation of WAN data access over data federations in CMS. A new emerging area of work is the exploitation of Intelligent Network Services, including also bandwidth on demand concepts. In this paper, we will review the work done in CMS on this, and the next steps.

The b quark forward–backward asymmetry has been measured using hadronic Z0 decays collected by the OPAL experiment at LEP. Z0→bb̄ decays were selected using a combination of secondary vertex and lepton tags, and the sign of the b quark charge was determined using an inclusive tag based on jet, vertex and kaon charges. The results, corrected to the quark level, are: AFBb=0.0582±0.0153±0.0012ats=89.50GeV,AFBb=0.0977±0.0036±0.0018ats=91.26GeV,AFBb=0.1221±0.0123±0.0025ats=92.91 GeV, where the first error is statistical and the second systematic in each case. Within the framework of the Standard Model, the result is interpreted as a measurement of the effective weak mixing angle for electrons of sin2θeff,eW=0.23205±0.00068.

The exclusive production of proton-antiproton pairs in the collisions of two quasi-real photons has been studied using data taken at $\sqrt{s_{ee}} = 183 $ GeV and 189 GeV with the OPAL detector at LEP. Results are presented for $p\bar{p}$ invariant masses, W, in the range 2.15<W<3.95 GeV. The cross-section measurements are compared with previous data and with recent analytic calculations based on t he quark-diquark model.

The CMS experiment at LHC started using the Resource Broker (by the EDG and LCG projects) to submit Monte Carlo production and analysis jobs to distributed computing resources of the WLCG infrastructure over 6 years ago. Since 2006 the gLite Workload Management System (WMS) and Logging & Bookkeeping (LB) are used. The interaction with the gLite-WMS/LB happens through the CMS production and analysis frameworks, respectively ProdAgent and CRAB, through a common component, BOSSLite. The important improvements recently made in the gLite-WMS/LB as well as in the CMS tools and the intrinsic independence of different WMS/LB instances allow CMS to reach the stability and scalability needed for LHC operations. In particular the use of a multi-threaded approach in BOSSLite allowed to increase the scalability of the systems significantly. In this work we present the operational set up of CMS production and analysis based on the gLite-WMS and the performances obtained in the past data challenges and in the daily Monte Carlo productions and user analysis usage in the experiment.

The Computing Model of the CMS experiment was prepared in 2005 and described in detail in the CMS Computing Technical Design Report. With the experience of the first years of LHC data taking and with the evolution of the available technologies, the CMS Collaboration identified areas where improvements were desirable. In this work we describe the most important modifications that have been, or are being implemented in the Distributed Computing Model of CMS. The Worldwide LHC computing Grid (WLCG) project acknowledged that the whole distributed computing infrastructure is impacted by this kind of changes that are happening in most LHC experiments and decided to create several Technical Evolution Groups (TEG) aiming at assessing the situation and at developing a strategy for the future. In this work we describe the CMS view on the TEG activities as well.

In a collaboration the size of CMS (approx. 3000 users, and almost 100 computing centres of varying size) communication and accurate information about the sites it has access to is vital in co-ordinating the multitude of computing tasks required for smooth running. SiteDB is a tool developed by CMS to track sites available to the collaboration, the allocation to CMS of resources available at those sites and the associations between CMS members and the sites (as either a manager/operator of the site or a member of a group associated to the site). It is used to track the roles a person has for an associated site or group. SiteDB eases the coordination load for the operations teams by providing a consistent interface to manage communication with the people working at a site, by identifying who is responsible for a given task or service at a site and by offering a uniform interface to information on CMS contacts and sites. SiteDB provides api's and reports for other CMS tools to use to access the information it contains, for instance enabling CRAB to use "user friendly" names when black/white listing CE's, providing role based authentication and authorisation for other web based services and populating various troubleshooting squads in external ticketing systems in use daily by CMS Computing operations.

The WLCG infrastructure moved from a very rigid network topology, based on the MONARC model, to a more relaxed system, where data movement between regions or countries does not necessarily need to involve T1 centres. While this evolution brought obvious advantages, especially in terms of flexibility for the LHC experiment's data management systems, it also opened the question of how to monitor the increasing number of possible network paths, in order to provide a global reliable network service. The perfSONAR network monitoring system has been evaluated and agreed as a proper solution to cover the WLCG network monitoring use cases: it allows WLCG to plan and execute latency and bandwidth tests between any instrumented endpoint through a central scheduling configuration, it allows archiving of the metrics in a local database, it provides a programmatic and a web based interface exposing the tests results; it also provides a graphical interface for remote management operations. In this contribution we will present our activity to deploy a perfSONAR based network monitoring infrastructure, in the scope of the WLCG Operations Coordination initiative: we will motivate the main choices we agreed in terms of configuration and management, describe the additional tools we developed to complement the standard packages and present the status of the deployment, together with the possible future evolution.

A search is described to detect charged Higgs bosons via the process e+e−→H+H−, using data collected by the OPAL detector at center-of-mass energies of 130–172 GeV with a total integrated luminosity of 25 pb−1. The decay channels are assumed to be H+→qq′ and H+→τ+ντ. No evidence for charged Higgs boson production is observed. The lower limit for its mass is determined to be 52 GeV at 95% confidence level, independent of the H+→τ+ντ branching ratio.

We have measured the mean charged particle multiplicities separately for bb̄, cc̄ and light quark (uū,dd̄,ss̄) initiated events produced in e+e− annihilations at LEP. The data were recorded with the OPAL detector at eleven different energies above the Z0 peak, corresponding to the full statistics collected at LEP1.5 and LEP2. The difference in mean charged particle multiplicities for bb̄ and light quark events, δbl, measured over this energy range is consistent with an energy independent behaviour, as predicted by QCD, but is inconsistent with the prediction of a more phenomenological approach which assumes that the multiplicity accompanying the decay of a heavy quark is independent of the quark mass itself. Our results, which can be combined into the single measurement δbl=3.44±0.40(stat)±0.89(syst) at a luminosity weighted average centre-of-mass energy of 195 GeV, are also consistent with an energy independent behaviour as extrapolated from lower energy data.

In this presentation we will discuss the early experience with the CMS computing model from the last large scale challenge activities through the first six months of data taking. Between the initial definition of the CMS Computing Model in 2004 and the start of high energy collisions in 2010, CMS exercised the infrastructure with numerous scaling tests and service challenges. We will discuss how those tests have helped prepare the experiment for operations and how representative the challenges were to the early experience with data taking. We will outline how the experiment operations has evolved during the first few months of operations. The current state of the Computing system will be presented and we will describe the initial experience with active users and real data. We will address the issues that worked well in addition to identifying areas where future development and refinement is needed.

The INFN Tier-1 located at CNAF in Bologna (Italy) is a center of the WLCG e-Infrastructure, supporting the 4 major LHC collaborations and more than 30 other INFN-related experiments. After multiple tests towards elastic expansion of CNAF compute power via Cloud resources (provided by Azure, Aruba and in the framework of the HNSciCloud project), and building on the experience gained with the production quality extension of the Tier-1 farm on remote owned sites, the CNAF team, in collaboration with experts from the ALICE, ATLAS, CMS, and LHCb experiments, has been working to put in production a solution of an integrated HTC+HPC system with the PRACE CINECA center, located nearby Bologna. Such extension will be implemented on the Marconi A2 partition, equipped with Intel Knights Landing (KNL) processors. A number of technical challenges were faced and solved in order to successfully run on low RAM nodes, as well as to overcome the closed environment (network, access, software distribution, ... ) that HPC systems deploy with respect to standard GRID sites. We show preliminary results from a large scale integration effort, using resources secured via the successful PRACE grant N. 2018194658, for 30 million KNL core hours.

During the first LHC run, the CMS experiment collected tens of Petabytes of collision and simulated data, which need to be distributed among dozens of computing centres with low latency in order to make efficient use of the resources. While the desired level of throughput has been successfully achieved, it is still common to observe transfer workflows that cannot reach full completion in a timely manner due to a small fraction of stuck files which require operator intervention.