Lorenzo Bianchini

An algorithm for reconstruction of the Higgs mass in H → ττ decays is presented. The algorithm computes for each event a likelihood function P(Mττ) which quantifies the level of compatibility of a Higgs mass hypothesis Mττ with measured momenta of the visible tau decay products plus the missing transverse energy reconstructed in the event. The algorithm is used in the CMS H → ττ analysis, where it is found to improve the sensitivity to discover the Standard Model Higgs boson in this decay channel by about 30%.

The result of a search at the LHC for heavy stable charged particles produced in pp collisions at $ \sqrt {s} = 7\;{\text{TeV}} $ is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 pb−1. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398GeV/c 2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c 2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

Hadronic event shapes have been measured in proton-proton collisions at sqrt(s)=7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 inverse picobarns. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.

A measurement of the top-antitop production cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV has been performed at the LHC with the CMS detector. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns and is based on the reconstruction of the final state with one isolated, high transverse-momentum electron or muon and three or more hadronic jets. The kinematic properties of the events are used to separate the top-antitop signal from W+jets and QCD multijet background events. The measured cross section is 173 + 39 - 32 (stat. + syst.) pb, consistent with standard model expectations.

The Italian institute for nuclear physics (INFN) has financed the SIMP project (2019–2021) in order to strengthen its skills and technologies in the field of meV detectors with the ultimate aim of developing a single microwave photon detector. This goal will be pursued by improving the sensitivity and the dark-count rate of two types of photodetectors: current-biased Josephson junction (CBJJ) for the frequency range 10–50 GHz and transition-edge sensor (TES) for the frequency range 30–100 GHz. Preliminary results on materials and devices characterization are presented.

We consider the problem of setting a confidence interval on a parameter of interest from a high-statistics counting experiment in the presence of systematic uncertainties modeled as unconstrained nuisance parameters. We use the profile-likelihood test statistic in the asymptotic limit for confidence interval setting and focus on the case where the likelihood function is derived from a finite sample of Monte Carlo simulated events. We prove as a general result that statistical uncertainties in the Monte Carlo sample affect the coverage of the confidence interval always in the same direction, namely they lead to a systematic undercoverage of the interval. We argue that such spurious effects might not be fully accounted for by statistical methods that are usually adopted in HEP measurements to counteract the effects of finite-size MC samples, such as those based on the Barlow-Beeston likelihood.

Abstract Josephson junctions, in appropriate configurations, can be excellent candidates for detection of single photons in the microwave frequency band. Such possibility has been recently addressed in the framework of galactic axion detection. Here are reported recent developments in the modelling and simulation of dynamic behaviour of a Josephson junction single microwave photon detector. For a Josephson junction to be enough sensitive, small critical currents and operating temperatures of the order of ten of mK are necessary. Thermal and quantum tunnelling out of the zero-voltage state can also mask the detection process. Axion detection would require dark count rates in the order of 0.001 Hz. It is, therefore, is of paramount importance to identify proper device fabrication parameters and junction operation point.

We illustrate a mathematical model for the evolution of multicellular tumour spheroids in a host tissue, including the effect of the excess H+ ions and the nutrient dynamics. Both the avascular and the vascular case are considered. The model is a nontrivial generalization of the simple scheme proposed in [K. Smallbone, D.J. Gavaghan, R.A. Gatenby, P.K. Maini, The role of acidity in solid tumour growth and invasion, J. Theoret. Biol. 235 (2005) 476–484]. Many different situations may occur, depending on the values of the physical parameters involved. Existence of solutions and qualitative properties are investigated.

We present an algorithm for the reconstruction of the Higgs mass in events with Higgs bosons decaying into a pair of τ leptons. The algorithm is based on matrix element (ME) techniques and achieves a relative resolution on the Higgs boson mass of typically 15–20%. A previous version of the algorithm has been used in analyses of Higgs boson production performed by the CMS collaboration during LHC Run 1. The algorithm is described in detail and its performance on simulated events is assessed. The development of techniques to handle τ decays in the ME formalism represents an important result of this paper.

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.

We consider a spin-$1$ resonance produced with an arbitrary spectrum of velocities and decaying into a pair of massless leptons, and we study the probability density function of the energy of the leptons in the laboratory frame. A special case is represented by the production of $W$ bosons in proton-proton collisions, for which the energy of the charged lepton from the decaying $W$ can be measured with sufficient accuracy for a high-precision measurement of $M_W$. We find that half of the resonance mass is a special value of the lepton energy, since the probability density function at this point is in general not analytic for a narrow-width resonance. In particular, the higher-order derivatives of the density function are likely to develop singularities, such as cusps or poles. A finite width of the resonance restores the regularity, for example by smearing cusps and poles into local stationary points. The quest for such points offers a handle to estimate the resonance mass with much reduced dependence on the underlying production and decay dynamics of the resonance.

A prototype for a sampling calorimeter made out of cerium fluoride crystals interleaved with tungsten plates, and read out by wavelength-shifting fibres, has been exposed to beams of electrons with energies between 20 and 150 GeV, produced by the CERN Super Proton Synchrotron accelerator complex. The performance of the prototype is presented and compared to that of a Geant4 simulation of the apparatus. Particular emphasis is given to the response uniformity across the channel front face, and to the prototype׳s energy resolution.

A group of Early-Career Researchers (ECRs) has been given a mandate from the European Committee for Future Accelerators (ECFA) to debate the topics of the current European Strategy Update (ESU) for Particle Physics and to summarise the outcome in a brief document [1]. A full-day debate with 180 delegates was held at CERN, followed by a survey collecting quantitative input. During the debate, the ECRs discussed future colliders in terms of the physics prospects, their implications for accelerator and detector technology as well as computing and software. The discussion was organised into several topic areas. From these areas two common themes were particularly highlighted by the ECRs: sociological and human aspects; and issues of the environmental impact and sustainability of our research.

Abstract The parton distribution functions (PDFs) of the proton play a role in determining the lineshape of Z and W bosons produced at the LHC. In particular, the mode of the gauge boson virtuality is shifted with respect to the pole due to the dependence of the partonic luminosity on the boson virtuality. The knowledge of this shift contributes to the systematic uncertainty for a direct measurement of the boson mass. A detailed study of the shift and of its systematic uncertainty due to the limited knowledge of the PDFs is obtained using a tree-level model of Z and W boson production in proton-proton collisions at $$\sqrt{s}=13~\hbox {TeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn><mml:mspace /><mml:mtext>TeV</mml:mtext></mml:mrow></mml:math> . A Monte Carlo simulation is further used to validate the tree-level model and study the dependence of the shift on the transverse momentum of the gauge bosons. The tree-level calculation is found to provide a good description of the shift. The systematic uncertainty on the lineshape due to the PDFs is estimated to be below one MeV in the phase-space relevant for a future high-precision mass measurement of the gauge boson masses at the LHC.

Talk includes LFV decays and FCNC top decays into a Higgs boson and a quark overlap with Talk on rare H decays to be discussed. Presented at LHCP2015 The 3rd Conference on Large Hadron Collider Physics Higgs boson plus heavy flavour: searches and measurements from the LHC Run 1 Lorenzo Bianchini (on behalf of the ATLAS and CMS Collaborations)1,a) 1ETH Zurich, Institute for Particle Physics, Otto-Stern-Weg 5, 8093 Zurich (Switzerland) a)lore.bianchini@gmail.com Abstract. This talk gives a review of the Run 1 ATLAS and CMS results on searches and measurements of Higgs bosons decaying to, or produced in association with heavy-flavour quarks (charm, bottom, and top quarks). The Standard Model of particle physics predicts that the Higgs boson interacts with the quarks through scalar, flavour-diagonal, Yukawa interactions, whose tree-level coupling strength is also fixed to be proportional to the quark mass. The detection of Higgs bosons decaying to a heavy flavour quark-antiquark pair (bottom and, to a smaller extent, charm quarks), or produced in association with heavy quarks (top and bottom quarks), is therefore the most favourable way to probe the quark Yukawa sector. This talk gives a review of the Run 1 ATLAS and CMS results on searches and measurements of Higgs bosons decaying to, or produced in association with heavy-flavour quarks (charm, bottom, and top quarks). The Standard Model of particle physics predicts that the Higgs boson interacts with the quarks through scalar, flavour-diagonal, Yukawa interactions, whose tree-level coupling strength is also fixed to be proportional to the quark mass. The detection of Higgs bosons decaying to a heavy flavour quark-antiquark pair (bottom and, to a smaller extent, charm quarks), or produced in association with heavy quarks (top and bottom quarks), is therefore the most favourable way to probe the quark Yukawa sector.

A precise determination of the Yukawa coupling to top quarks is crucial for the characterization of the recently discovered Higgs boson. A direct measurement of this coupling can be provided only by those processes where the Higgs boson is produced in association with top quarks. In the Standard Model (SM), the production of the Higgs boson together with a top-antitop pair (tt‾H) has the largest cross section, followed by the production with a single top quark (tH), with roughly one order of magnitude smaller rate. As of summer 2014, the CMS experiment at LHC has performed searches for either processes using the full Run-I data set in a variety of decay channels of the Higgs boson, namely H→WW⁎,ZZ⁎,τ+τ−,bb‾,γγ for the tt‾H production, and H→γγ for tH. Due to the small cross section, the sensitivity to the SM tH production is still far from being achieved, yet stringent constraints can be already set for non-SM couplings. Conversely, the combination of the various tt‾H searches has already attained sensitivity to measure a SM-like signal, providing a best-fit value of the signal strength modifier μˆ=2.76−0.92+1.05, compatible with the SM expectation at the 2σ level. An improved tt‾H search in the H→γγ channel using the full 7 and 8 TeV data set, as well as a new tt‾H, H→bb‾ analysis using a matrix element technique, are here presented for the first time.

Owing to its large mass, the top quark is expected to play a special role in the electroweak symmetry breaking of the Standard Model. The measurement of the Higgs boson coupling to the top quark is therefore of the highest theoretical relevance, but is also experimentally rather challenging. In this review, results from the ATLAS and CMS collaborations on the searches for the production of a Standard Model Higgs boson in association with top quarks are discussed, including the latest results from the Run 2 of the LHC.

In this thesis, I present my work in the CMS experiment on a search for the standard model Higgs boson decaying into a pair of tau leptons. The original goal and the final aim of this research is a contribution to the discovery of the Higgs boson at the LHC. After a summary of the theoretical framework and of the experimental apparatus, I will describe the particle-flow technique developed for the offline CMS event reconstruction. Tau reconstruction and identification in CMS are described. Particular emphasis is devoted to the discrimination between the electrons and tau leptons decaying semi-leptonically (giving hadrons and neutrinos). A crucial and challenging aspect in the search for the Higgs boson decaying into tau leptons is the reconstruction of the di-tau mass. On this subject, I have provided original contributions in the development of a new likelihood-based technique, called SVfit, which is then used for the analysis. Finally, a search for the Standard Model Higgs boson in the di-tau channel, based on 4.9 1/fb of pp collisions at sqrt(s) = 7 TeV, is presented. Events are selected where one tau decays semi-leptonically and the other decays fully- leptonically into neutrinos and lighter charged leptons (electrons or muons). No significant excess over the Standard Model backgrounds is observed. The statistical interpretation of the results is then translated into 95% CL upper limits on the signal cross-section.

Dans cette these, je presente mon travail effectue au sein de l'experience CMS, et consacre a la recherche du boson de Higgs du modele standard dans sa voie de desintegration en une paire de leptons tau. L'objectif original et la finalite de cette recherche est une contribution a la decouverte du boson de Higgs au LHC. Apres un resume du cadre theorique et experimental de ma these, j'expose la technique particle-fow developpee pour la reconstruction des evenements hors ligne enregistres par CMS. La reconstruction et l'identification des leptons tau dans CMS sont decrites en detail dans la these. Une attention particuliere est consacree a la discrimination entre les electrons et les leptons taus qui se desintegrant en voie semi-leptoniques (donnant des neutrinos et des hadrons). Un element crucial dans l'etude H -> tautau est la reconstruction de la masse invariante. Sur ce sujet, j'ai apporte des contributions originales au developpement d'un Dynamical Likelihood Model, appele SVfit, pour estimer la masse totale de la paire des taus, et qui sera utilise pour l'analyse. Enfin, une recherche du boson de Higgs SM dans la voie H -> tautau , base sur 4. 9 1/fb de collisions pp a sqrt(s) = 7 TeV, est presentee. Des evenements avec une paire de taus sont selectionnes ou l'un se desintegre de facon semi-leptonique (i. E. En hadrons et neutrinos) et l'autre en facon leptonique (i. E. En muons ou electrons et en neutrinos). Aucun exces par dessus aux bruits de fond predicts par le SM n'a ete observe. L'interpretation statistique des resultats a ete faite dans le cadre du SM et elle est finalement traduite en limites au 95% CL sur la section efficace du signal

This chapter is devoted to the statistical treatment of experimental data. By its very nature, the outcome of a particle physics experiment is a to be considered as random process: the theory of probability thus provides the correct theoretical framework. A few concepts are of key importance in data analysis. After recalling a few outstanding theorems, the properties of the likelihood function areLikelihood function illustrated by considering simple cases that can be handled analytically, i.e. without the use of computer programs. The focus is then put on the combination of random variables, error propagation, and the construction of frequentist confidence intervals.

The subject of the third chapter is the motion of charged particles induced by electromagneticElectromagnetic fields. The first section focuses on the kinematics of charged particles inside static fields and its application for particle trackingTracking . The second section is dedicated to the physics of accelerators. The last section is devoted to the concept of luminosityLuminosity and event rates at colliders.

The subject of the second chapter is the interaction of particles with matter. The first section discusses the mechanism by which various types of particles interact with different media. Particular emphasis is given to the concept of energy loss and range in matter. The second section focuses on the experimental techniques for particle identificationParticle identification . The third section is dedicated to the functioning of particle detectors.

The first chapter is dedicated to the kinematics of relativistic particles. The starting point is the introduction of the Lorentz groupLorentz group through its representations. Large emphasis then is given to the transformation properties of velocities and angles. The centre-of-mass dynamics is studied in detail for two-to-two scattering and for two- and three-body decays. The last part of the chapter is devoted to the concept of cross section, which plays a central role in particle physics.

The problems collected in the fifth chapter deal with particle physics from a more theoretical perspective. They are mostly concerned with the phenomenological predictions of Standard Model of particle interactions. After introducing the concept of symmetry, which is of cardinal importance in the formulation of a good theory, the proposed exercises will focus on the physicsStandard model of particle interactions of electroweakElectroweak interaction and strong interactions. The two last sections are dedicated to flavour physicsFlavour and to the Higgs bosonHiggs boson .

Vengono presentate le attivita di ricerca svolte nei vari Dipartimenti di Architettura e Ingegneria delle Universita Italiane nell'ambito del raggruppamento scientifico disciplinare ICAR 17- Disegno.

One of the main relevant topics of Industry 4.0 is related to the prediction of Remaining Useful Life (RUL) of machines. In this context, the “Smart Manufacturing Machine with Predictive Lifetime Electronic maintenance” (SIMPLE) project aims to promote collaborations among different companies in the scenario of predictive maintenance. One of the topics of the SIMPLE project is related to the prediction of RUL of automated teller machines (ATMs). This represents a key task as these machines are subject to different types of failure. However the main challenges in this field lie in: i) collecting a representative dataset, ii) correctly annotating the observations and iii) handling the imbalanced nature of the dataset. To overcome this problem, in this work we present a feature extraction strategy and a machine learning (ML) based solution for solving RUL estimation for ATM devices. We prove the effectiveness of our approach with respect to other state-of-the-art ML approaches widely employed for solving the RUL task. In addition, we propose the design of a predictive maintenance platform to integrate our ML model for the SIMPLE project.

This book presents more than 300 exercises on topics that span the experimental and the theoretical aspects of particle physics.