G. Dissertori

The flavour changing neutral current decay b→sγ has been detected in hadronic Z decays collected by ALEPH at LEP. The signal is isolated in lifetime-tagged bb̄ events by the presence of a hard photon associated with a system of high momentum and high rapidity hadrons. The background processes are normalised from the data themselves. The inclusive branching ratio is measured to be(3.11±0.80stat±0.72syst)×10−4,consistent with the Standard Model expectation via penguin processes.

Many highly developed Monte Carlo tools for the evaluation of cross sections based on tree matrix elements exist and are used by experimental collaborations in high energy physics. As the evaluation of one-loop matrix elements has recently been undergoing enormous progress, the combination of one-loop matrix elements with existing Monte Carlo tools is on the horizon. This would lead to phenomenological predictions at the next-to-leading order level. This note summarises the discussion of the next-to-leading order multi-leg (NLM) working group on this issue which has been taking place during the workshop on Physics at TeV colliders at Les Houches, France, in June 2009. The result is a proposal for a standard interface between Monte Carlo tools and one-loop matrix element programs.

Abstract We apply an Adversarially Learned Anomaly Detection (ALAD) algorithm to the problem of detecting new physics processes in proton–proton collisions at the Large Hadron Collider. Anomaly detection based on ALAD matches performances reached by Variational Autoencoders, with a substantial improvement in some cases. Training the ALAD algorithm on 4.4 fb $$^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> of 8 TeV CMS Open Data, we show how a data-driven anomaly detection and characterization would work in real life, re-discovering the top quark by identifying the main features of the $$t \bar{t}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>t</mml:mi> <mml:mover> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> </mml:math> experimental signature at the LHC.

A search has been performed for the Standard Model Higgs boson in the data sample collected with the ALEPH detector at LEP, at centre-of-mass energies up to 209GeV. An excess of 3sigma beyond the background expectation is found, consistent with the production of the Higgs boson with a mass near 114GeV/c2. Much of this excess is seen in the four-jet analyses, where three high purity events are selected.

The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991–1995. A semi-exclusive reconstruction of B→ℓνD(★) decays is performed, by combining lepton candidates with fully reconstructed D(★) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xBwd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be 〈xBwd〉=0.716±0.006(stat)±0.006(syst), using a model-independent method; the corresponding value for the energy of the leading B meson is 〈xBL〉=0.736±0.006(stat)±0.006(syst). The reconstructed spectra are compared with different fragmentation models.

We present the first determination of the strong coupling constant from a fit of next-to-next-to-leading order QCD predictions to event-shape variables, measured in $e^+e^-$ annihilations at LEP. The data have been collected by the ALEPH detector at centre-of-mass energies between 91 and 206 GeV. Compared to results of next-to-leading order fits we observe that the central fit values are lower by about 10%, with considerably reduced scatter among the results obtained with different event-shape variables. The dominant systematic uncertainty from renormalization scale variations is reduced by a factor of two. By combining the results for several event-shape variables and centre-of-mass energies, we find α_s(M_Z^2) = 0.1240+-0.0008(stat)+-0.0010(exp)+-0.0011(had)+-0.0029(theo).

This Report summarizes the proceedings of the 2015 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) the new PDF4LHC parton distributions, (III) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (IV) a host of phenomenological studies essential for comparing LHC data from Run I with theoretical predictions and projections for future measurements in Run II, and (V) new developments in Monte Carlo event generators.

We present a first computation of the next-to-next-to-leading order (NNLO) QCD cross-section at the LHC for the production of four leptons from a Higgs boson decaying into W bosons. We study the cross-section for a mass value of Mh = 165 GeV; around this value a Standard Model Higgs boson decays almost exclusively into W-pairs. We apply all nominal experimental cuts on the final state leptons and the associated jet activity and study the magnitude of higher-order effects up to NNLO on all kinematic variables which are constrained by experimental cuts. We find that the magnitude of the higher-order corrections varies significantly with the signal selection cuts. As a main result we give the value of the cross-section at NNLO with all selection cuts envisaged for the search of the Higgs boson.

We present a determination of the strong coupling constant from a fit of QCD predictions for six event-shape variables, calculated at next-to-next-to-leading order (NNLO) and matched to resummation in the next-to-leading-logarithmic approximation (NLLA). These event shapes have been measured in e+e− annihilations at LEP, where the data we use have been collected by the ALEPH detector at centre-of-mass energies between 91 and 206 GeV. Compared to purely fixed order NNLO fits, we observe that the central fit values are hardly affected, but the systematic uncertainty is larger because the NLLA part re-introduces relatively large uncertainties from scale variations. By combining the results for six event-shape variables and eight centre-of-mass energies, we find

We propose a new strategy for anomaly detection at the LHC based on unsupervised quantum machine learning algorithms. To accommodate the constraints on the problem size dictated by the limitations of current quantum hardware we develop a classical convolutional autoencoder. The designed quantum anomaly detection models, namely an unsupervised kernel machine and two clustering algorithms, are trained to find new-physics events in the latent representation of LHC data produced by the autoencoder. The performance of the quantum algorithms is benchmarked against classical counterparts on different new-physics scenarios and its dependence on the dimensionality of the latent space and the size of the training dataset is studied. For kernel-based anomaly detection, we identify a regime where the quantum model significantly outperforms its classical counterpart. An instance of the kernel machine is implemented on a quantum computer to verify its suitability for available hardware. We demonstrate that the observed consistent performance advantage is related to the inherent quantum properties of the circuit used.

As a consequence of the COVID-19 pandemic, most courses at a large technical university were adapted so that students had a free choice of whether to attend lectures on-site or online; in addition, in many courses, lecture recordings were available. At the subsequent exam session, over 17,000 student-survey responses were collected regarding attendance choices, learning behavior, interest in the course, perception of the exam, and recommendations to future students. A total of 27 learner attributes and their relationships were investigated. In addition, conditional attributes and free-response statements were analyzed, and the students' exam grades were retrieved to gauge their performance. We found only minute differences with respect to exam performance, but the analysis indicates distinctly different preferences and constraints in taking advantage of learning opportunities. We also found some indications that performance differences might be larger for interactive-engagement courses. The results of the analysis may be key to answering why at many universities, faculty report that live-lecture attendance has decreased more strongly than expected with the availability of new, virtual attendance modes.

The anticipated performance of calorimeter crystals in the environment expected after the planned High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN has to be well understood, before informed decisions can be made on the need for detector upgrades. Throughout the years of running at the HL-LHC, the detectors will be exposed to considerable fluences of fast hadrons that have been shown to cause cumulative transparency losses in Lead Tungstate scintillating crystals. In this study, we present direct evidence of the main underlying damage mechanism. Results are shown from a test that yields a direct insight into the nature of the hadron-specific damage in Lead Tungstate calorimeter crystals exposed to 24 GeV/c protons.

We have developed two quantum classifier models for the $t\bar{t}H(b\bar{b})$ classification problem, both of which fall into the category of hybrid quantum-classical algorithms for Noisy Intermediate Scale Quantum devices (NISQ). Our results, along with other studies, serve as a proof of concept that Quantum Machine Learning (QML) methods can have similar or better performance, in specific cases of low number of training samples, with respect to conventional ML methods even with a limited number of qubits available in current hardware. To utilise algorithms with a low number of qubits -- to accommodate for limitations in both simulation hardware and real quantum hardware -- we investigated different feature reduction methods. Their impact on the performance of both the classical and quantum models was assessed. We addressed different implementations of two QML models, representative of the two main approaches to supervised quantum machine learning today: a Quantum Support Vector Machine (QSVM), a kernel-based method, and a Variational Quantum Circuit (VQC), a variational approach.

A Cerium Fluoride crystal produced during early R&D studies for calorimetry at the CERN Large Hadron Collider was exposed to a 24 GeV/c proton fluence Phi_p=(2.78 +- 0.20) x 10EE13 cm-2 and, after one year of measurements tracking its recovery, to a fluence Phi_p=(2.12 +- 0.15) x 10EE14 cm-2. Results on proton-induced damage to the crystal and its spontaneous recovery after both irradiations are presented here, along with some new, complementary data on proton-damage in Lead Tungstate. A comparison with FLUKA Monte Carlo simulation results is performed and a qualitative understanding of high-energy damage mechanism is attempted.

Axial PET is a novel geometrical concept for Positron Emission Tomography (PET), based on layers of long scintillating crystals axially aligned with the bore axis. The axial coordinate is obtained from arrays of wavelength shifting (WLS) plastic strips placed orthogonally to the crystals. This article describes the design, construction and performance evaluation of a demonstrator set-up which consists of two identical detector modules, used in coincidence. Each module comprises 48 LYSO crystals of 100 mm length and 156 WLS strips. Crystals and strips are readout by Geiger-mode Avalanche Photo Diodes (G-APDs). The signals from the two modules are processed by fully analog front-end electronics and recorded in coincidence by a VME-based data acquisition system. Measurements with point-like 22Na sources, with the modules used both individually and in coincidence mode, allowed for a complete performance evaluation up to the focal plane reconstruction of point sources. The results obtained are in good agreement with expectations and proved the set-up to be ready for the next evaluation phase with PET phantoms filled with radiotracers.

Lutetium-Yttrium Orthosilicate doped with Cerium (LYSO), as a bright scintillating crystal, is a candidate for calorimetry applications in strong ionising-radiation fields and large high-energy hadron fluences are expected at the CERN Large Hadron Collider after the planned High-Luminosity upgrade. There, proton–proton collisions will produce fast hadron fluences up to ~5×1014cm−2 in the large-rapidity regions of the calorimeters. The performance of LYSO has been investigated, after exposure to different fluences of 24 GeV c−1 protons. Measured changes in optical transmission as a function of proton fluence are presented, and the evolution over time due to spontaneous recovery at room temperature is studied. The activation of materials will also be an issue in the described environment. Studies of the ambient dose induced by LYSO and its evolution with time, in comparison with other scintillating crystals, have also been performed through measurements and FLUKA simulations.

The amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique. The amplitude reconstruction has been studied with test beam data recorded from a fully equipped barrel supermodule. Issues specific to data taken in the test beam are investigated, and the implementation of the method for CMS data taking is discussed.

The Tevatron experiments have recently excluded a Standard Model Higgs boson in the mass range 160 GeV < mH < 170 GeV at the 95% confidence level. This result is based on sophisticated analyses designed to maximize the ratio of accepted signal to background. In this paper we study the production of a Higgs boson of mass mH = 160 GeV in the gg → H → WW → lνlν channel. We choose a set of cuts like those adopted in the experimental analysis and compare kinematical distributions of the final state leptons computed in NNLO QCD to lower-order calculations and to those obtained with the event generators PYTHIA, HERWIG and MC@NLO. We also show that the distribution of the output from an Artificial Neural Network obtained with the different tools does not show significant differences. However, the final acceptance computed with PYTHIA is smaller than those obtained at NNLO and with HERWIG and MC@NLO. We also investigate the impact of the underlying event and hadronization on our results.

This report summarizes the activities of the SM and NLO Multileg Working Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 2009.

This is a preliminary update of the measurements of αs and the determination of the world average value of αs (M2Z) presented in the 2013/2014 edition of the Review of Particle Properties [1].

The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> pi+ pi-. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.

Software for Tomographic Image Reconstruction (STIR) is an open-source library for PET and SPECT image reconstruction, implementing iterative reconstruction as well as 2D- and 3D-filtered back projection. Quantitative reconstruction of PET data requires the knowledge of the scanner geometry. Typical scanners, clinical as well as pre-clinical ones, use a block-type geometry. Several rectangular blocks of crystals are arranged into regular polygons. Multiple of such polygons are arranged along the scanner axis. However, the geometrical representation of a scanner provided by STIR is a cylinder made of rings of individual crystals equally distributed in axial and transaxial directions. The data of realistic scanners are projected onto such virtual scanners prior to image reconstruction. This results in reduced quality of the reconstructed image. In this study, we implemented the above-described block geometry into the STIR library, permitting the image reconstruction without the interpolation step. In order to evaluate the difference in image quality, we performed Monte Carlo simulation studies of three different scanner designs: two scanners with multiple crystals per block and one with a single crystal per block. Simulated data were reconstructed using the standard STIR method and the newly implemented block geometry.Visual comparison between the images reconstructed by the two models for the block-type scanners shows that the new implementation enhances the image quality to the extent that the results before normalization correction are comparable with those after normalization correction. The simulation result of a uniform cylinder shows that the coefficient of variation decreases from 25.8% to 20.9% by using the new implementation in STIR. Spatial resolution is enhanced resulting in a lower partial loss of intensity in sources of small size, e.g., the spill-over ratio for spherical sources of 1.8 mm diameter is 0.19 in the block and 0.34 in the cylindrical model.Results indicate a significant improvement for the new model in comparison with the old one which mapped the polygonal geometry into a cylinder. The new implementation was tested and is available for use via the library of Swiss Federal Institute of Technology in Zurich (ETH).

We show that an Ansatz to resum all leading and next-to-leading logarithms in the theoretical prediction for the 2-jet rate in e+e− → hadrons, where jets are defined with the kt-algorithm, is consistent with a full O(αs2) calculation done by Monte Carlo integration. From the asymptotic behaviour of the full O(αs2) calculation we extract the subleading coefficient G21 and the constant C2.

Starting from a sample of four million hadronic Z decays collected with the ALEPH detector at LEP, 404 charged and neutral B mesons are fully reconstructed and used to look for resonant structure in the Bπ system. An excess of events is observed above the expected background in the Bπ mass spectrum at a mass ≈5.7 GeV/c2, consistent with the production and decay to B(∗)π of the B∗∗ states predicted by Heavy Quark Symmetry (HQS). In the framework of HQS, it is found that the mass of the B2∗ state is (5739+8−11(stat)+6−4(syst))MeV/c2 and the relative production rate of the B∗∗ system is BR(b→B∗∗→B(∗)π)/BR(b→Bu,d)=(31±9(stat)+6−5(syst))%. In the same sample of B mesons, significant Bπ± charge-flavour correlations are observed, which may prove important for tagging the initial B state in future CP violation studies.

Data taken with the ALEPH detector at LEP1 have been used to search for gamma gamma production of the glueball candidates f0(1500) and fJ(1710) via their decay to pi+pi-. No signal is observed and upper limits to the product of gamma gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have been measured to be Gamma_(gamma gamma -&gt; f0(1500)). BR(f0(1500)-&gt;pi+pi-) &lt; 0.31 keV and Gamma_(gamma gamma -&gt; fJ(1710)). BR(fJ(1710)-&gt;pi+pi-) &lt; 0.55 keV at 95% confidence level.

A simulation of the search for the Standard Model Higgs boson at the LHC, in the channel gg→H→WW→ℓνℓν, is described. Higher-order QCD corrections are taken into account by using a reweighting procedure, which allows us to combine event rates obtained with the PYTHIA Monte Carlo program with the most up-to-date theoretical predictions for the transverse-momentum spectra of the Higgs signal and its corresponding WW background. With this method the discovery potential for Higgs masses between 140 and 180 GeV is recalculated and the potential statistical significance of this channel is found to increase considerably. For a Higgs mass of 165 GeV a signal-to-background ratio of almost 2:1 can be obtained. A statistical significance of five standard deviations might already be achieved with an integrated luminosity close to 0.4 fb−1. Using this approach, an experimental effective K-factor of about 2.04 is obtained for the considered Higgs signature, which is only about 15% smaller than the theoretical inclusive K-factor.

Performance tests of some aspects of the CMS ECAL were carried out on modules of the "barrel" sub-system in 2002 and 2003. A brief test with high energy electron beams was made in late 2003 to validate prototypes of the new Very Front End electronics. The final versions of the monitoring and cooling systems, and of the high and low voltage regulation were used in these tests. The results are consistent with the performance targets including those for noise and overall energy resolution, required to fulfil the physics programme of CMS at the LHC.

The discovery of a Standard Model Higgs boson is possible when experimental cuts are applied which increase the ratio of signal and background cross-sections. In this paper we study the pp → H → WW signal cross-section at the LHC which requires a selection of Higgs bosons with small transverse momentum. We compare predictions for the efficiency of the experimental cuts from a NNLO QCD calculation, a calculation of the resummation of logarithms in the transverse momentum of the Higgs boson at NNLL, and the event generator MC@NLO. We also investigate the impact of various jet-algorithms, the underlying event and hadronization on the signal cross-section.

Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated.

This report summarizes the activities of the NLM working group of the Workshop Physics at TeV Colliders, Les Houches, France, 11-29 June, 2007.

We present a determination of the strong coupling constant αsmZ using inclusive top-quark pair production cross section measurements performed at the LHC and at the Tevatron. Following a procedure first applied by the CMS Collaboration, we extract individual values of αsmZ from measurements by different experiments at several centre-of-mass energies, using QCD predictions complete in NNLO perturbation theory, supplemented with NNLL approximations to all orders, and suitable sets of parton distribution functions. The determinations are then combined using a likelihood-based approach, where special emphasis is put on a consistent treatment of theoretical uncertainties and of correlations between various sources of systematic uncertainties. Our final combined result is αsmZ=0.1177-0.0036+0.0034 .

Quantum machine learning provides a fundamentally novel and promising approach to analyzing data. However, many data sets are too complex for currently available quantum computers. Consequently, quantum machine learning applications conventionally resort to dimensionality reduction algorithms, e.g., auto-encoders, before passing data through the quantum models. We show that using a classical auto-encoder as an independent preprocessing step can significantly decrease the classification performance of a quantum machine learning algorithm. To ameliorate this issue, we design an architecture that unifies the preprocessing and quantum classification algorithms into a single trainable model: the guided quantum compression model. The utility of this model is demonstrated by using it to identify the Higgs boson in proton-proton collisions at the LHC, where the conventional approach proves ineffective. Conversely, the guided quantum compression model excels at solving this classification problem, achieving a good accuracy. Additionally, the model developed herein shows better performance compared to the classical benchmark when using only low-level kinematic features.

Abstract The ECAL Barrel and MTD Barrel Timing Layer subdetectors of CMS are approaching series production of electronic boards, including voltage conditioning PCBs: LVRs and PCCs respectively. 2448 LVRs and 864 PCCs will be installed during LS3 of the LHC. These boards are hosting radiation-tolerant bPOL12V ASICs which convert a broad input voltage range into required voltage levels for microelectronics between 1.2–2.5 V. Each card must be tested multiple times at various production stages to ensure its conformity. This contribution describes a methodology of testing bPOL12V conversion quality including the detection of instability regions at certain load levels.

We study a phenomenological ansatz for merging next-to-next-to-leading order (NNLO) calculations with Monte Carlo event generators. We reweight them to match bin-integrated NNLO differential distributions. To test this procedure, we study the Higgs boson production cross-section at the LHC, for which a fully differential partonic NNLO calculation is available. We normalize PYTHIA and MC@NLO Monte Carlo events for Higgs production in the gluon fusion channel to reproduce the bin integrated NNLO double differential distribution in the transverse momentum and rapidity of the Higgs boson. These events are used to compute differential distributions for the photons in the pp→H→γγ decay channel, and are compared to predictions from fixed-order perturbation theory at NNLO. We find agreement between the reweighted generators and the NNLO result in kinematic regions where we expect a good description using fixed-order perturbation theory. Kinematic boundaries where resummation is required are also modeled correctly using this procedure. We then use these events to compute distributions in the pp→H→W+W−→l+l−ν channel, for which an accurate description is needed for measurements at the LHC. We find that the final state lepton distributions obtained from PYTHIA are not significantly changed by the reweighting procedure.

The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of √s = 7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9  fb^(-1), respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26^(+0.31)_(−0.26).

The data collected at centre-of-mass energies of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 176.2 pb−1, are analysed in a search for pair-produced charged Higgs bosons H±. Three analyses are employed to select the τ+νττ−ν̄τ, cs̄τ−ν̄τ and cs̄sc̄ final states. No evidence for a signal is found. Upper limits are set on the production cross section as a function of the branching fraction B(H+→τ+ντ) and of the mass mH±, assuming that the sum of the branching ratios is equal to one. In the framework of a two-Higgs-doublet model, charged Higgs bosons with masses below 65.4 GeV/c2 are excluded at 95% confidence level independently of the decay mode.

The HERA electron--proton collider has collected 100 pb$^{-1}$ of data since its start-up in 1992, and recently moved into a high-luminosity operation mode, with upgraded detectors, aiming to increase the total integrated luminosity per experiment to more than 500 pb$^{-1}$. HERA has been a machine of excellence for the study of QCD and the structure of the proton. The Large Hadron Collider (LHC), which will collide protons with a centre-of-mass energy of 14 TeV, will be completed at CERN in 2007. The main mission of the LHC is to discover and study the mechanisms of electroweak symmetry breaking, possibly via the discovery of the Higgs particle, and search for new physics in the TeV energy scale, such as supersymmetry or extra dimensions. Besides these goals, the LHC will also make a substantial number of precision measurements and will offer a new regime to study the strong force via perturbative QCD processes and diffraction. For the full LHC physics programme a good understanding of QCD phenomena and the structure function of the proton is essential. Therefore, in March 2004, a one-year-long workshop started to study the implications of HERA on LHC physics. This included proposing new measurements to be made at HERA, extracting the maximum information from the available data, and developing/improving the theoretical and experimental tools. This report summarizes the results achieved during this workshop.

Ensuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered.

The SAFIR development represents a novel Positron Emission Tomography (PET) detector, conceived for preclinical fast acquisitions inside the bore of a Magnetic Resonance Imaging (MRI) scanner. The goal is hybrid and simultaneous PET/MRI dynamic studies at unprecedented temporal resolutions of a few seconds. The detector relies on matrices of scintillating LSO-based crystals coupled one-to-one with SiPM arrays and readout by fast ASICs with excellent timing resolution and high rate capabilities. The paper describes the detector concept and the initial results in terms of simulations and characterisation measurements.

The small animal fast insert for mRi (SAFIR) positron emission tomography insert was proposed for quantitative dynamic acquisition inside a preclinical 7T magnetic resonance imaging scanner to study kinetics of short-lived tracers. For this purpose, the SAFIR readout should be capable of handling high count rates and achieving excellent timing performance. We evaluated one of the available application specific integrated circuits (ASICs) for SiPM readout, namely SiPM timing chip (STiC) version 3.1. In this paper, we show the performances of the SAFIR PET detector with the STiC ASIC readout. The SAFIR PET detector consists of an 8 x 8 array of lutetium yttrium oxyorthosilicate 2.1 mm x 2.1 mm x 12 mm crystals coupled, with optical grease, to an 8 x 8 array of SiPMs with a 2.0 mm x 2.0 mm photo-sensitive area. Signals from the individual SiPM channels were digitized by the STiC ASIC. Hit's arrival time and time-over-threshold (TOT) were recorded into time stamps with 50.2-ps least significant bit. We obtained an average energy resolution of 18.5% full width at half maximum (FWHM) at 511-keV photopeak after TOT nonlinearity correction and an average coincidence resolving time resolution of 244-ps FWHM with time walk correction that satisfy our requirements specification on the detector performance.

The SAFIR prototype insert is a preclinical Positron Emission Tomography (PET) scanner built to acquire dynamic images simultaneously with a 7 T Bruker Magnetic Resonance Imaging (MRI) scanner. The insert is designed to perform with an excellent coincidence resolving time of 194 ps Full Width Half Maximum (FWHM) and an energy resolution of 13.8% FWHM. These properties enable it to acquire precise quantitative images at activities as high as 500 MBq suitable for studying fast biological processes within short time frames (< 5 s). In this study, the performance of the SAFIR prototype insert is evaluated according to the NEMA NU 4-2008 standard while the insert is inside the MRI without acquiring MRI data.Applying an energy window of 391-601 keV and a coincidence time window of 500 ps the following results are achieved. The average spatial resolution at 5 mm radial offset is 2.6 mm FWHM when using the Filtered Backprojection 3D Reprojection (FBP3DRP) reconstruction method, improving to 1.2 mm when using the Maximum Likelihood Expectation Maximization (MLEM) method. The peak sensitivity at the center of the scanner is 1.06%. The Noise Equivalent count Rate (NECR) is 799 kcps at the highest measured activity of 537 MBq for the mouse phantom and 121 kcps at the highest measured activity of 624 MBq for the rat phantom. The NECR peak is not yet reached for any of the measurements. The scatter fractions are 10.9% and 17.8% for the mouse and rat phantoms, respectively. The uniform region of the image quality phantom has a 3.0% STD, with a 4.6% deviation from the expected number of counts per voxel. The spill-over ratios for the water and air chambers are 0.18 and 0.17, respectively.The results satisfy all the requirements initially considered for the insert, proving that the SAFIR prototype insert can obtain dynamic images of small rodents at high activities ([Formula: see text] 500 MBq) with a high sensitivity and an excellent count-rate performance.

Inclusive γ∗γ interactions to hadronic final states where one scattered electron or positron is detected in the electromagnetic calorimeters have been studied in the LEP 1 data taken by ALEPH from 1991 to 1995. The event sample has been used to measure the hadronic structure function of the photon F2γ in three bins with 〈Q2〉 of 9.9, 20.7 and 284 GeV2.

The process e+e− → hA is used to search for the Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM), in the bbbb and τ+τ−bb final states. The search is performed in the data collected by the ALEPH experiment at LEP, at centre-of-mass energies between 130 and 172 GeV and with a total luminosity of 27.2 pb−1. No candidate events are found in either of the final states, in agreement with the expected background of 0.91 events from all Standard Model processes. Combined with searches for e+e− → hZ, this results in a 95% C.L. lower limit on the masses of both h and A of 62.5 GeV/c2, for tan β > 1.

The e+e−→ZZ cross section at s=182.7 and 188.6GeV has been measured using the ALEPH detector. A cut-based analysis yields cross section measurements ofσZZ(182.7GeV)=0.11±0.160.11(stat.)±0.04(syst.)pbandσZZ(188.6GeV)=0.69±0.130.12(stat.)±0.03(syst.)pb.A neural network-based analysis yieldsσZZ(188.6GeV)=0.64±0.120.11(stat.)±0.04(syst.)pb.These measurements are consistent with the Standard Model expectations.

A search for pair-production of long-lived, heavy, singly-charged particles has been performed with data collected by the ALEPH detector at a centre-of-mass energy of 172 GeV. Data at \sqrt{s} = 161, 136, and 130 GeV are also included to improve the sensitivity to lower masses. No candidate is found in the data. A model-independent 95% confidence level upper limit on the production cross section at 172 GeV of 0.2-0.4pb is derived for masses between 45 and 86 GeV/c^2. This cross section limit implies, assuming the MSSM, a lower limit of 67 (69) GeV/c^2 on the mass of right- (left-) handed long-lived scalar taus or scalar muons and of 86 GeV/c^2 on the mass of long-lived charginos.

We describe the concept and first experimental tests of a novel 3D axial Positron Emission Tomography (PET) geometry. It allows for a new way of measuring the interaction point in the detector with very high precision. It is based on a matrix of long Lutetium-Yttrium OxyorthoSilicate (LYSO) crystals oriented in the axial direction, each coupled to one Geiger Mode Avalanche Photodiode (G-APD) array. To derive the axial coordinate, Wave Length Shifter (WLS) strips are mounted orthogonally and interleaved between the crystals. The light from the WLS strips is read by custom-made G-APDs. The weighted mean of the signals in the WLS strips has proven to give very precise axial resolution. The achievable resolution along the three axes is mainly driven by the dimensions of the LYSO crystals and WLS strips. This concept is inherently free of parallax errors. Furthermore, it will allow identification of Compton interactions in the detector and for reconstruction of a fraction of them, which is expected to enhance image quality and sensitivity. We present the results of proof-of-principle tests and qualification measurements of the various components prepared to build a larger scale demonstrator consisting of two matrices of 8×6 LYSO crystals and 312 WLS strips.

This report summarizes the activities of the NLM working group of the Workshop "Physics at TeV Colliders", Les Houches, France, 11-29 June, 2007.

The Mu3e experiment searches for charged lepton flavor violation in the rare decay μ→eee with a projected sensitivity of 10−16. A precise measurement of the decay product momenta, decay vertex and time is necessary for background suppression at rates of 109 muons/s. This can be achieved by combining an ultra-lightweight pixel tracker based on HV-MAPS with two timing systems. The trigger-less readout of the detector with three stages of FPGA-boards over multi GBit/s optical links into a GPU filter farm is presented. In this scheme data from all sub-detectors is merged and distributed in time slices to the filter farm.

The SAFIR collaboration is currently developing a high-rate positron emission tomography (PET) insert to study fast kinetic processes in small animals. Our insert is designed for simultaneous image acquisition with a preclinical 7 T magnetic resonance (MR) imaging device. In contrast to existing preclinical PET scanners and inserts, our hardware is optimized for high-rate measurements with source activities up to 500 MBq. As a first step, the SAFIR Prototype insert was constructed. This already incorporates the final components, but has a reduced axial field-of-view (35.6 mm). We use lutetiumyttrium oxyorthosilicate crystals (2.12 mm × 2.12 mm × 13 mm) one-to-one coupled to silicon photomultipliers. All analog signals are digitized within the insert. We use 49 MR-compatible dc- dc converters in the insert to provide the power to all readout electronics. After shimming, no degradation of the homogeneity of the static B0 field in the MR scanner was observed. During full operation, we saw a minor reduction in the signal-to-noise ratio of the MR data of 4.9%. With a low activity point source (22Na 0.65 MBq) we obtained a coincidence energy resolution of 13.8% full width at half maximum (FWhM) and a coincidence timing resolution of 194 ps (FWhM). First PET/MR rat brain and high-rate mouse cardiac images (84.9 MBq) are shown in this article.

The data collected by the ALEPH experiment at LEP at centre–of–mass energies around 183 GeV are analysed to search for sleptons, the partners of leptons in supersymmetric theories. The previously published search for acoplanar leptons and missing energy has been updated. New searches have been developed to cover a wider range of slepton signals. These include single electrons, acoplanar leptons accompanied by two photons plus missing energy as well as particles with lifetime. No evidence for the production of any such particles is found. Slepton mass limits are reported within gravity mediated and gauge mediated SUSY breaking scenarios.

The data collected at a centre-of-mass energy of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 173.6 pb−1, are analysed in a search for the scalar partners of quarks and leptons predicted in supersymmetric models. No evidence for any such particles was found in the decay channels ℓ̃→ℓχ, t̃→cχ, t̃→bℓν̃, b̃→bχ, and q̃→qχ. Improved mass lower limits have been obtained in the framework of the Minimal Supersymmetric Standard Model.

A new measurement of the mean lifetime of the τ lepton is presented. Three different analysis methods are applied to a sample of 90 000 τ pairs, collected in 1993 and 1994 with the ALEPH detector at LEP. The average of this measurement and those previously published by ALEPH is ττ = 290.1 ± 1.5 ± 1.1 fs.

In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995, the B0s→D(∗)+sD(∗)−s decay is observed, based on tagging the final state with two φ mesons in the same hemisphere. The Ds(∗)+Ds(∗)− final state is mostly CP even and corresponds to the short-lived B0s mass eigenstate. The branching ratio of this decay is measured to be BR(B0s(short)→D(∗)+sD(∗)−s) =(23±10−9+19)%. A measurement of the lifetime of the B0s(short) gives 1.27±0.33±0.08 ps. The lifetime and branching ratio measurements provide two essentially independent methods of estimating the relative decay width difference ΔΓ/Γ in the B0s–B̄0s system, corresponding to an average value ΔΓ/Γ=(25+21−14)%.

Searches for neutral Higgs bosons are performed with the 237 pb-1 of data collected in 1999 by the ALEPH detector at LEP, for centre-of-mass energies between 191.6 and 201.6 GeV. These searches apply to Higgs bosons within the context of the Standard Model and its minimal supersymmetric extension (MSSM) as well as to invisibly decaying Higgs bosons. No evidence of a signal is seen. A lower limit on the mass of the Standard Model Higgs boson of 107.7 GeV/c2 at 95% confidence level is set. In the MSSM, lower limits of 91.2 and 91.6 GeV/c2 are derived for the masses of the neutral Higgs bosons h and A, respectively. For a Higgs boson decaying invisibly and produced with the Standard Model cross section, masses below 106.4 GeV/c2 are excluded.

A novel geometry for a sampling calorimeter employing inorganic scintillators as an active medium is presented. To overcome the mechanical challenges of construction, an innovative light collection geometry has been pioneered, that minimises the complexity of construction. First test results are presented, demonstrating a successful signal extraction. The geometry consists of a sampling calorimeter with passive absorber layers interleaved with layers of an active medium made of inorganic scintillating crystals. Wavelength-shifting (WLS) fibres run along the four long, chamfered edges of the stack, transporting the light to photodetectors at the rear. To maximise the amount of scintillation light reaching the WLS fibres, the scintillator chamfers are depolished. It is shown herein that this concept is working for cerium fluoride (CeF3) as a scintillator. Coupled to it, several different types of materials have been tested as WLS medium. In particular, materials that might be sufficiently resistant to the High- Luminosity Large Hadron Collider radiation environment, such as cerium-doped Lutetium- Yttrium Orthosilicate (LYSO) and cerium-doped quartz, are compared to conventional plastic WLS fibres. Finally, an outlook is presented on the possible optimisation of the different components, and the construction and commissioning of a full calorimeter cell prototype is presented.

The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO4 crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO4 crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 1013 and 1.3× 1014 cm−2. These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb−1 and 3000 fb−1 respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.

The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 10.65 pb−1 collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 GeV. The invariant mass distribution of simulated events are fitted to the experimental distributions and the following W masses are obtained:WW→qq̄qq̄,mW=81.30±0.47(stat.)±0.11(syst.)GeV/c2,WW→ℓνqq̄(ℓ=e,μ),mW=80.54±0.47(stat.)±0.11(syst.)GeV/c2,WW→τνqq̄,mW=79.56±1.08(stat.)±0.23(syst.)GeV/c2.The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data. The combination of these three measurements gives:mW=80.80±0.32(stat.)±0.11(syst.)±0.03(LEPenergy)GeV/c2.

A new concept of a monolithic pixel radiation detector is presented. It is based on the deposition of a film of hydrogenated amorphous silicon (a-Si:H) on an Application Specific Integrated Circuit (ASIC). For almost 20 years, several research groups tried to demonstrate that a-Si:H material could be used to build radiation detectors for particle physics applications. A novel approach is made by the deposition of a-Si:H directly on the readout ASIC. This technique is similar to the concept of monolithic pixel detectors, but offers considerable advantages. We present first results from tests of a n–i–p a-Si:H diode array deposited on a glass substrate and on the a-Si:H above ASIC prototype detector.

Integrated particle sensors have been developed using thin-film on ASIC technology. For this purpose, hydrogenated amorphous silicon diodes, in various configurations, have been optimized for particle detection. These devices were first deposited on glass substrates to optimize the material properties and the dark current of very thick diodes (with thickness up to 50 μm). Corresponding diodes were later directly deposited on CMOS readout chips. These integrated particle sensors have been characterized using light pulse illumination and beta particle irradiation from 63Ni and 90Sr sources. Direct detection of single low- and high-energy beta particles have been demonstrated. The application of this new integrated particle sensor concept for medical imaging is also discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The strong coupling constant is one of the fundamental parameters of the standard model of particle physics. In this review I will briefly summarise the theoretical framework, within which the strong coupling constant is defined and how it is connected to measurable observables. Then I will give an historical overview of its experimental determinations and discuss the current status and world average value. Among the many different techniques used to determine this coupling constant in the context of quantum chromodynamics, I will focus in particular on a number of measurements carried out at the Large Electron Positron Collider (LEP) and the Large Hadron Collider (LHC) at CERN.

Searches for supersymmetric particles in channels with one or more photons and missing energy have been performed with data collected by the ALEPH detector at LEP. The data consist of 11.1 pb-1 at $\sqrt{s} = 161 GeV$, 1.1 pb-1 at 170 GeV and 9.5 pb-1 at 172 GeV. The e+e- -> nunu+photon cross section is measured. The data are in good agreement with predictions based on the Standard Model, and are used to set upper limits on the cross sections for anomalous photon production. These limits are compared to two different SUSY models and used to set limits on the neutralino mass. A limit of 71 GeV/c^2 at 95% C.L. is set on the mass of the lightest neutralino ($\tau_{\chi_{1}^{0}} \leq $ 3 ns) for the gauge-mediated supersymmetry breaking and LNZ models.

Using a sample of four million hadronic Z events collected in ALEPH from 1991 to 1995, the decays D∗+→D0πs+, with D0 decaying to K−π+ or to K+π−, are studied. The relative branching ratio B(D0→K+π−)/B(D0→K−π+) is measured to be 1.84±0.59(stat.) ±0.34(syst.)%. The two possible contributions to the D0→K+π− decay, doubly Cabibbo-suppressed decays and D0–D̄0 mixing, are disentangled by measuring the proper-time distribution of the reconstructed D0's. Assuming no interference between the two processes, the upper limit obtained on the mixing rate is 0.92% at95%CL. The possible effect of interference between the two amplitudes is also assessed.

The production of W+W− pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb−1. Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71±0.34(stat.)±0.18(syst.)pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be B(W→hadrons)=66.97±0.65(stat.)±0.32(syst.)%, allowing a determination of the CKM matrix element |Vcs|=0.951±0.030(stat.)±0.015(syst.).

We study predictions from perturbative Quantum Chromodynamics (QCD) for the process pp→H→γγ+X . In particular, we compare fully differential calculations at next-to-leading (NLO) and next-to-next-to-leading order (NNLO) in the strong coupling constant to the results obtained with the MC@NLO Monte Carlo (MC) generator, which combines QCD matrix elements at NLO with a parton shower algorithm. Estimates for the systematic uncertainties in the various predictions due to the choice of the renormalization scale and the parton distribution functions are given for the inclusive and accepted cross sections and for the corresponding acceptance corrections, obtained after applying standard selection and acceptance cuts. Furthermore, we compare the distributions for the Higgs signal to those for the irreducible two-photon background, obtained with a NLO MC simulation.

We present the experimental results obtained with a novel monolithic silicon pixel detector which consists in depositing a n–i–p hydrogenated amorphous silicon (a-Si:H) diode straight above the readout ASIC (this technology is called Thin Film on ASIC, TFA). The characterization has been performed on 13 and 30 μm thick a-Si:H films deposited on top of an ASIC containing a linear array of high-speed low-noise transimpedance amplifiers designed in a 0.25 μm CMOS technology. Experimental results presented have been obtained with a 600 nm pulsed laser. The results of charge collection efficiency and charge collection speed of these structures are discussed.

Firsts results on particle detection using a novel silicon pixel detector are presented. The sensor consists of an array of 48 square pixels with 380 μm pitch based on a n–i–p hydrogenated amorphous silicon (a-Si:H) film deposited on top of a VLSI chip. The deposition was performed by VHF-PECVD, which enables high rate deposition up to 2 nm/s. Direct particle detection using beta particles from 63Ni and 90Sr sources was performed.

We present the prototype of a dedicated brain Positron Emission Tomography system BPET and the results of a first NEMA (NU2-2018 & NU4-2008) performance evaluation. BPET is a modular system, based on the PETA6SE application specific integrated circuit and LYSO crystals coupled in light sharing mode to silicon photomultipliers. All electronics are integrated into the detector head, which makes the system ultra-compact. The NU2-2018 spatial resolution in the axial center in [radial/tangential/axial] direction at r=10 mm is [4.0 / 3.9 / 3.5] mm full width at half maximum. The NU2-2018 system sensitivity is 2.9 cps/kBq for the smallest energy window at the radial center. It is 8.4 cps/kBq for the largest energy window considered at r=10 cm. We further show results of a noise equivalent count rate evaluation and BPET reconstructed images from a brain image quality phantom and a 3D Hoffman brain phantom. The performance characteristics of the BPET prototype are comparable to current clinical systems. BPET is the basis for the development of a clinical low-cost ultra-compact, fully integrated brain Positron Emission Tomography system.

SAFIR (Small Animal Fast Insert for mRi) is an innovative, high rate, PET detector insert for MRI, to be used for quantitative dynamic pre-clinical imaging, with very high activities injected in the animals, up to 500 MBq. The PET detector will be designed to allow for ultra short acquisition periods (of the order of a few seconds) simultaneously with the MRI, permitting unprecedented temporal resolutions in preclinical dynamic multimodal imaging. High sensitivity (~ 6%), high spatial resolution (~1.5 mm FWHM), excellent coincidence timing resolution (CTR ~ 300 ps FWHM) and a fast DAQ system able to cope with the huge data throughput are required. Parallel with the hardware efforts, dedicated 4D algorithms for image reconstruction must be developed. The overall state of the project will be presented, including ongoing activities towards the choice and characterization of the detector components (crystals, SiPMs and readout chips), MonteCarlo simulations, and first reconstruction of various simulated sources. Special emphasis will be given to the results of a recent high rate test, where the TOFPET ASIC has been tested with Hamamatsu S12642-0404PB-50 SiPM arrays coupled to matrices of LYSO:Ce crystals (3.1x3.1x12 mm3 each), exposed to a 500 MBq activity of FDG radiotracer in a volume of about 0.5 cm3.

The reaction e+e− → HZ is used to search for the Standard Model Higgs boson. The data sample consists of integrated luminosities of 10.9 pb−1, 1.1 pb−1, and 9.5 pb−1 collected by the ALEPH experiment at LEP during 1996, at centre-of-mass energies of 161, 170 and 172 GeV, respectively. No candidate events were found, in agreement with the expected background of 0.84 events from all Standard Model processes. This search results in a 95% C.L. lower limit on the Higgs boson mass of 69.4 GeV/c2. When combined with earlier ALEPH searches performed at energies at and around the Z peak, this limit increases to 70.7 GeV/c2.

Bose-Einstein correlations are studied in semileptonic (WW→qq̄ℓν) and fully hadronic (WW→qq̄qq̄) W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189 GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einstein correlations based on the JETSET hadronization scheme was tuned to the Z data and reproduces the correlations in the WW→qq̄ℓν events. The same Monte Carlo reproduces the correlations in the WW→qq̄qq̄ channel assuming independent fragmentation of the two W's. A variant of this model with Bose-Einstein correlations between decay products of different W's is disfavoured.

Two-particle correlations of ΛΛ and Λ̄Λ̄ pairs have been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q<2 GeV which could arise from the effects of Fermi–Dirac statistics. In addition the spin content of the Λ pair system has been determined. For Q>2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q<2 GeV this fraction is found to be lower. For ΛΛ̄ pairs, where no Fermi–Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range.

Data collected at centre-of-mass energies from 189 GeV to 202 GeV by the ALEPH detector at LEP corresponding to an integrated luminosity of 411 pb−1, are analysed in a search for the scalar top in the decay channels t̃→c/uχ for small mass differences between the stop and the lightest neutralino. No evidence for deviations from the Standard Model expectation is found and a lower limit of 59 GeV/c2 is set for the stop mass, independent of the stop to neutralino mass difference and of the stop lifetime.

The HERA electron--proton collider has collected 100 pb$^{-1}$ of data since its start-up in 1992, and recently moved into a high-luminosity operation mode, with upgraded detectors, aiming to increase the total integrated luminosity per experiment to more than 500 pb$^{-1}$. HERA has been a machine of excellence for the study of QCD and the structure of the proton. The Large Hadron Collider (LHC), which will collide protons with a centre-of-mass energy of 14 TeV, will be completed at CERN in 2007. The main mission of the LHC is to discover and study the mechanisms of electroweak symmetry breaking, possibly via the discovery of the Higgs particle, and search for new physics in the TeV energy scale, such as supersymmetry or extra dimensions. Besides these goals, the LHC will also make a substantial number of precision measurements and will offer a new regime to study the strong force via perturbative QCD processes and diffraction. For the full LHC physics programme a good understanding of QCD phenomena and the structure function of the proton is essential. Therefore, in March 2004, a one-year-long workshop started to study the implications of HERA on LHC physics. This included proposing new measurements to be made at HERA, extracting the maximum information from the available data, and developing/improving the theoretical and experimental tools. This report summarizes the results achieved during this workshop.

The design and construction of a PET camera module with high sensitivity, full 3-D spatial reconstruction and very good energy resolution is presented. The basic principle consists of an axial arrangement of long scintillation crystals around the Field Of View (FOV), providing a measurement of the transverse coordinates of the interacting 511 keV gamma ray. On top of each layer of crystals, an array of Wave-Length Shifter (WLS) strips, which collect the light leaving the crystals sideways, is positioned orthogonal to the crystal direction. The signals in the WLS strips allow a precise measurement of the z (axial) co-ordinate of the 511 keV γ-ray gamma impact. The construction of two modules used for demonstration of the concept is described. First preliminary results on spatial and energy resolution from one full module will be shown.

Abstract Standard Positron Emission Tomography (PET) cameras need to reach a compromise between spatial resolution and sensitivity. To overcome this limitation we developed a novel concept of PET. Our AX-PET demonstrator is made of LYSO crystals aligned along the z coordinate (patient's axis) and WLS strips orthogonally placed with respect to the crystals. This concept offers full 3D localization of the photon interaction inside the camera. Thus the spatial resolution and the sensitivity can be simultaneously improved and the reconstruction of Compton interactions inside the detector is also possible. Moreover, by means of G-APDs for reading out the photons, both from LYSO and WLS, the detector is insensitive to magnetic fields and it is then suitable to be used in a combined PET/MRI apparatus. A complete Monte Carlo simulation and dedicated reconstruction software have been developed. The two final modules, each composed of 48 crystals and 156 WLS strips, have been built and fully characterized in a dedicated test set-up. The results, obtained with a 22 Na point source (0.25 mm diameter), of the single module performances and a first estimation of the performances with the two module system are reported.

This is the summary report of the energy frontier QCD working group prepared for Snowmass 2013. We review the status of tools, both theoretical and experimental, for understanding the strong interactions at colliders. We attempt to prioritize important directions that future developments should take. Most of the efforts of the QCD working group concentrate on proton-proton colliders, at 14 TeV as planned for the next run of the LHC, and for 33 and 100 TeV, possible energies of the colliders that will be necessary to carry on the physics program started at 14 TeV. We also examine QCD predictions and measurements at lepton-lepton and lepton-hadron colliders, and in particular their ability to improve our knowledge of strong coupling constant and parton distribution functions.

The data collected by ALEPH at LEP at centre-of-mass energies ranging from 181 to 184 GeV, corresponding to an integrated luminosity of 57 pb−1, are analysed to search for pair-produced neutral Higgs bosons h and A, in the bb̄bb̄ and τ+τ−bb̄ final states. Two events are found in the data with 2.5 expected from standard model processes. When combined with the lower energy data collected by ALEPH and with earlier reported searches for associated hZ production, these analyses are interpreted in the context of the minimal supersymmetric extension of the standard model (MSSM). For standard choices of MSSM parameter sets, this combination results in 95% C.L. exclusion lower limits of 72.2 and 76.1 GeV/c2 for mh and mA, irrespective of tanβ. A scan of the MSSM parameter space is performed in which the model parameters are varied over wide ranges. For low values of tanβ, i.e., for 1<tanβ≲2, the limit on mh of ∼88 GeV/c2 is shown to be robust, being satisfied in essentially all of the physically allowed domain.

Single W production is studied in the data recorded with the ALEPH detector at LEP at centre-of-mass energies between 161 and 183 GeV. The cross section is measured to be σW=0.41±0.17(stat.)±0.04(syst.) pb at 183 GeV, consistent with the Standard Model expectation. Limits on non-standard WWγ couplings are deduced as −1.6<κγ<1.5(λγ=0) and −1.6<λγ<1.6(κγ=1) at 95% C.L. A search for effectively invisible decays of the W boson in W pair production is performed, leading to an upper limit on the branching ratio of 1.3% (Γinv=27MeV) at 95% C.L.

Abstract A prototype of the safety system for the electromagnetic calorimeter (ECAL) of the CMS detector at LHC has been implemented and tested in Super Modules SM0 and SM1 during the ECAL test-beam campaign in summer 2003. The aim was to examine the system performance thoroughly and to resolve several open issues regarding the final system design. The performed tests mainly focused on the readout system performance, its calibration and noise problems. Furthermore, irradiation tests of the readout electronics components with a 64 MeV proton beam up to an equivalent cumulative dose of 200 kGy and 3.2×10 14 neutron cm −2 have been performed at the Paul Scherrer Institute in spring 2004. The results of all these tests are very promising, leading to the conclusion that the tested prototype offers an excellent basis for the development of the safety system for the entire CMS ECAL.

The Small Animal Fast Insert for mRi (SAFIR) will be a PET insert for the Bruker BioSpin 70/30. It aims at applications where fast processes such as blood perfusion in the rodent brain are to be monitored comprehensively and non-invasively. Employing electronics originally designed for time-of-flight applications, coincidence resolving times of less than a nanosecond can be achieved allowing for short coincidence time windows. Consequently, random contributions to the coincidence events are suppressed, making short acquisition frames with very high tracer concentrations possible. This will allow collecting sufficient count statistics in a few seconds. Geant4-based Monte Carlo simulations were used to characterize the performance of the reference design consisting of polished LSO-like crystals, one-to-one coupled to Silicon Photomultipliers. The crystals are grouped into 8×8 matrices, which are arranged into 24 modules and 10 rings. Similar methods as described in the NEMA NU 4-2008 standard were employed. The simulation results on NECR, sensitivity, and spatial resolution will be presented. Most notably, the NECR at 500 MBq is almost nine times higher than at 50 MBq for the given scanner. Combined with a very high sensitivity, this allows for short acquisition times using these very high injected doses. In addition, essentially random-free measurements at standard activities below 50 MBq are possible.

We describe our R&D effort to develop radiation-hard scintillating and wavelength shifting fibers by doping fused-silica with cerium. This new type of cerium-doped fiber potentially offers myriad new applications in calorimeters for high-energy physics, tracking systems, and profiling of charged particle beams.

Scintillating ceramics are a promising, new development for various applications in science and industry. Their application in calorimetry for particle physics experiments is expected to involve an exposure to high levels of ionizing radiation. In this paper, changes in performance have been measured for scintillating ceramic samples of different composition after exposure to penetrating ionizing radiation up to a dose of 38 kGy.

Studies have been done and continue on the design and construction of a Shashlik detector using Radiation hard quartz capillaries filled with wavelength shifting liquid to collect the scintillation light from LYSO crystals for use as a calorimeter in the Phase II CMS upgrade at CERN. The work presented here focuses on the studies of the capillaries and liquids that would best suit the purpose of the detector. Comparisons are made of various liquids, concentrations, and capillary construction techniques will be discussed.

The data collected in 1998 by ALEPH at LEP at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.2 pb−1, are analysed to search for invisible decays of a Higgs boson produced in the reaction e+e−→hZ. The number of events found in the data and their properties are in agreement with the Standard Model expectation. This search results in an improved 95% C.L. lower limit on the Higgs boson mass of 95.4 GeV/c2, assuming it decays totally invisibly and for a production cross section equal to that of the Standard Model.

The data collected at centre-of-mass energies ranging from 130 to 172 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 27.5 pb−1, are analysed in a search for pair-produced charged Higgs bosons H±. Three analyses are employed to select the τ+νττ−ν̄τ, cs̄τ−ν̄τ and cs̄sc̄ final states. No evidence for a signal is found. Mass limits are set as a function of the branching fraction B(τν) for H±→τν. Charged Higgs bosons with masses below 52 GeV/c2 are excluded at 95% C.L. independently of B(τν), thus significantly improving on existing limits.

Final states with charged kaons in three-prong τ decays are studied by exploiting the particle identification from the dE/dx measurement. The results are based on a sample of about 1.6 × 105 detected τ pairs collected with the ALEPH detector between 1991 and 1995 around the Z peak. The following branching ratios have been measured: B(τ- → K−K+π−ντ) = (1.63 ± 0.21 ± 0.17) × 10−3, B(τ− → K−π+π−ντ) = (2.14 ± 0.37 ± 0.29) × 10−3, B(τ− → K−K+π−π0ντ) = (0.75 ± 0.29 ± 0.15) × 10−3, and B(τ− → K−π+π−π0ντ) = (0.61 ± 0.39 ± 0.18) × 10−3. The first two measurements are more precise than the current world averages, while the last two channels are investigated for the first time. The 95% C.L. upper limit on the branching ratio for the decay τ− → K−K+K−ντ is 0.19 × 10−3. A study of intermediate states occurring in the K−K+π−ντ and K−π+π−ντ decays is also presented.

AX-PET is a novel PET detector based on axially oriented crystals and orthogonal wavelength shifter (WLS) strips, both individually read out by silicon photo-multipliers. Its design decouples sensitivity and spatial resolution, by reducing the parallax error due to the layered arrangement of the crystals. Additionally the granularity of AX-PET enhances the capability to track photons within the detector yielding a large fraction of inter-crystal scatter events. These events, if properly processed, can be included in the reconstruction stage further increasing the sensitivity. Its unique features require dedicated Monte-Carlo simulations, enabling the development of the device, interpreting data and allowing the development of reconstruction codes. At the same time the non-conventional design of AX-PET poses several challenges to the simulation and modeling tasks, mostly related to the light transport and distribution within the crystals and WLS strips, as well as the electronics readout. In this work we present a hybrid simulation tool based on an analytical model and a Monte-Carlo based description of the AX-PET demonstrator. It was extensively validated against experimental data, providing excellent agreement.

Abstract The AX-PET collaboration has developed a novel concept for high resolution PET imaging to overcome some of the performance limitations of classical PET cameras, in particular the compromise between spatial resolution and sensitivity introduced by the parallax error. The detector consists of an arrangement of long LYSO scintillating crystals axially oriented around the field of view together with arrays of wave length shifter strips orthogonal to the crystals. This matrix allows a precise 3D measurement of the photon interaction point. This is valid both for photoelectric absorption at 511 keV and for Compton scattering down to deposited energies of about 100 keV. Crystals and WLS strips are individually read out using Geiger-mode Avalanche Photo Diodes (G-APDs). The sensitivity of such a detector can be adjusted by changing the number of layers and the resolution is defined by the crystal and strip dimensions. Two AX-PET modules were built and fully characterized in dedicated test set-ups at CERN, with point-like 22 Na sources. Their performance in terms of energy ( R energy ≈ 11.8 % (FWMH) at 511 keV) and spatial resolution was assessed ( σ axial ≈ 0.65 mm ), both individually and for the two modules in coincidence. Test campaigns at ETH Zurich and at the company AAA allowed the tomographic reconstructions of more complex phantoms validating the 3D reconstruction algorithms. The concept of the AX-PET modules will be presented together with some characterization results. We describe a count rate model which allows to optimize the planing of the tomographic scans.

In recent years graphical processing units (GPUs) have become a powerful tool in scientific computing. Their potential to speed up highly parallel applications brings the power of high performance computing to a wider range of users. However, programming these devices and integrating their use in existing applications is still a challenging task. In this paper we examined the potential of GPUs for two different applications. The first application, created at Paul Scherrer Institut (PSI), is used for parameter fitting during data analysis of μSR (muon spin rotation, relaxation and resonance) experiments. The second application, developed at ETH, is used for PET (Positron Emission Tomography) image reconstruction and analysis. Applications currently in use were examined to identify parts of the algorithms in need of optimization. Efficient GPU kernels were created in order to allow applications to use a GPU, to speed up the previously identified parts. Benchmarking tests were performed in order to measure the achieved speedup. During this work, we focused on single GPU systems to show that real time data analysis of these problems can be achieved without the need for large computing clusters. The results show that the currently used application for parameter fitting, which uses OpenMP to parallelize calculations over multiple CPU cores, can be accelerated around 40 times through the use of a GPU. The speedup may vary depending on the size and complexity of the problem. For PET image analysis, the obtained speedups of the GPU version were more than ×40 larger compared to a single core CPU implementation. The achieved results show that it is possible to improve the execution time by orders of magnitude.

Enormous efforts at accelerators and experiments all around the world have gone into the search for the long-sought Higgs boson, postulated almost five decades ago. This search has culminated in the discovery of a Higgs-like particle by the ATLAS and CMS experiments at CERN's Large Hadron Collider in 2012. Instead of describing this widely celebrated discovery, in this article I will rather focus on earlier attempts to discover the Higgs boson, or to constrain the range of possible masses by interpreting precise data in the context of the Standard Model of particle physics. In particular, I will focus on the experimental efforts carried out during the last two decades, at the Large Electron Positron collider, CERN, Geneva, Switzerland, and the Tevatron collider, Fermilab, near Chicago, IL, USA.

A search for γγ decays of a Higgs boson is performed in the data sample collected at LEP with the ALEPH detector between 1991 and 1999. This corresponds to an integrated luminosity of 672 pb−1 at centre-of-mass energies ranging from 88 to 202 GeV. The search is based on topologies arising from a Higgs boson produced in association with a fermion pair via the Higgs-strahlung process e+e−→Hff̄, with ff̄=νν̄,e+e−,μ+μ−,τ+τ− or qq̄. Twenty-two events are selected in the data, while 28 events are expected from standard model processes. An upper limit is derived, as a function of the Higgs boson mass, on the product of the e+e−→Hff̄ cross section and the H→γγ branching fraction. In particular, a fermiophobic Higgs boson produced with the standard model cross section is excluded at 95% confidence level for all masses below 100.7GeV/c2.

AX-PET stands for a new geometrical concept for a high resolution and high sensitivity PET scanner, based on an axial arrangement of long scintillating crystals in the tomograph, for a parallax free PET detector. Two identical AX-PET modules – consisting of matrices of LYSO crystals interleaved with WLS strips – have been built. They form the AX-PET Demonstrator, which has been extensively characterized and successfully used for the reconstruction of images of several phantoms. In this paper we report on the current status of the project, with emphasis on the most relevant results achieved both in terms of detector characterization and image reconstruction. We also discuss the recent preliminary results obtained with the digital SiPM from Philips (dSiPM), which are currently being tested as a possible alternative photodetector for AX-PET. With their very good intrinsic time resolution, dSiPM could add Time of Flight capability to the AX-PET concept.

This paper presents the current architecture of the control and safety systems designed and implemented for the Electromagnetic Calorimeter (ECAL) of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). An evaluation of system performance during all CMS physics data taking periods is reported, with emphasis on how software and hardware solutions are used to overcome limitations, whilst maintaining and improving reliability and robustness. The outcomes of the CMS ECAL Detector Control System (DCS) Software Analysis Project were a fundamental step towards the integration of all control system applications and the consequent piece-by-piece software improvements allowed a smooth transition to the latest revision of the system. The ongoing task of keeping the system in-line with new hardware technologies and software platforms specified by the CMS DCS Group is discussed. The structure of the comprehensive support service with detailed incident logging is presented in addition to a complete test setup for reproducing failures and for testing solutions prior to deployment into production. A correlation between the acquired experience, the development of new software tools and a reduction in the DCS support load is highlighted.

During 1997 the ALEPH experiment at LEP gathered 57pb−1 of data at centre-of-mass energies near 183 GeV. These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e+e−→HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: mH>87.9GeV/c2 at 95% confidence level.

The data recorded by the ALEPH experiment at LEP at centre-of-mass energies of 161 GeV and 172 GeV were analysed to search for sleptons, the supersymmetric partners of leptons. No evidence for the production of these particles was found. The number of candidates observed is consistent with the background expected from four-fermion processes and gammagamma-interactions. Improved mass limits at 95% C.L. are reported.

Single top production via flavour changing neutral currents in the reactions e+e−→t̄c/u is searched for in approximately 411 pb−1 of data collected by ALEPH at centre-of-mass energies in the range between 189 and 202 GeV. In total, 58 events are selected in the data to be compared with 50.3 expected from Standard Model backgrounds. No deviation from the Standard Model expectation is observed. Upper limits at 95% CL on single top production cross sections at s=189–202 GeV are derived. A model-dependent limit on the sum of branching ratios BR(t→Zc)+BR(t→Zu)<17% is obtained.

The lifetimes of the B0 and B− mesons are measured using a sample of about four million hadronic Z decays collected from 1991 to 1995 with the Aleph detector at LEP. The data sample has been recently reprocessed, achieving a substantial improvement in the tracking performance. Semileptonic decays of B0 and B− mesons are partially reconstructed by identifying events containing a lepton with an associated D★+ or D0 meson. The proper time of the B meson is estimated from the measured decay length and the momentum of the D-lepton system. A fit to the proper time of 1880 D★+ℓ− and 2856 D0ℓ− candidates yields the following results: τB0=1.518±0.053±0.034 ps, τB−=1.648±0.049±0.035 ps, τB−/τB0=1.085±0.059±0.018.