A CMS kísérlet Barrel Müon Helyzetmeghatározó Rendszerének kalibrációja, validációja és működtetése

A doktori disszertáció célja a CERN (Európai Nukleáris Kutatási Szervezet, Conseil Européen pour la Recherche Nucléaire) intézet Nagy Hadron Ütköztető (LHC, Large Hadron Collider) gyorsítójánál működő Kompakt Müon Szolenoid (CMS, Compact Muon Solenoid) kísérlet Barrel Muon Spektrométer pozíció meghatározó rendszerének építésevel, validációjával és üzemeltetésével kapcsolatban végezett munkám ismertetése.The aim of the PhD thesis is to describe my work on the construction, installation, validation and operation of the position monitoring (called also alignment) system of the Barrel Muon Spectrometer of the CMS (Compact Muon Solenoid) experiment located in the P5 experimental hall of the Large Hadron Collider (LHC) accelerator at CERN (Conseil Européen pour la Recherche Nucléaire

Search for physics beyond the standard model in high-mass diphoton events from proton-proton collisions at root s=13 TeV

A search for physics beyond the standard model is performed using a sample of high-mass diphoton events produced in proton-proton collisions at $\sqrt{s} =$ 13 TeV. The data sample was collected in 2016 with the CMS detector at the LHC and corresponds to an integrated luminosity of 35.9 fb$^{-1}$. The search is performed for both resonant and nonresonant new physics signatures. At 95% confidence level, lower limits on the mass of the first Kaluza-Klein excitation of the graviton in the Randall-Sundrum warped extra-dimensional model are determined to be in the range of 2.3 to 4.6 TeV, for values of the associated coupling parameter between 0.01 and 0.2. Lower limits on the production of scalar resonances and model-independent cross section upper limits are also provided. For the large extra-dimensional model of Arkani-Hamed, Dimopoulos, and Dvali, lower limits are set on the string mass scale $M_S$ ranging from 5.6 to 9.7 TeV, depending on the model parameters. The first exclusion limits are set in the two-dimensional parameter space of a continuum clockwork model

Search for supersymmetry in events with a τ lepton pair and missing transverse momentum in proton-proton collisions at √s=13 TeV

A search for the electroweak production of supersymmetric particles in proton-proton collisions at a center-of-mass energy of 13 TeV is presented in final states with a $\tau$ lepton pair. Both hadronic and leptonic decay modes are considered for the $\tau$ leptons. Scenarios involving the direct pair production of $\tau$ sleptons, or their indirect production via the decays of charginos and neutralinos, are investigated. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected with the CMS detector in 2016. The observed number of events is consistent with the standard model background expectation. The results are interpreted as upper limits on the cross section for $\tau$ slepton pair production in different scenarios. The strongest limits are observed in the scenario of a purely left-handed $\tau$ slepton with a mass of 90 GeV decaying to a nearly massless neutralino, and correspond to 1.26 times the expected production cross section in the simplified model considered. Exclusion limits are also set in the context of simplified models of chargino-neutralino and chargino pair production with decays to $\tau$ leptons, and range up to 710 and 630 GeV, respectively

Measurement of differential cross sections for Z boson production in association with jets in proton-proton collisions at √s=13TeV

The production of a Z boson, decaying to two charged leptons, in association with jets in proton- proton collisions at a centre- of- mass energy of 13 TeV is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19 fb - 1. The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the Z boson, the jet kinematic variables ( transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance in transverse momentum between the reconstructed jet recoil and the Z boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes oneloop corrections. The third is a fixed- order calculation with next- to- next- to- leading order accuracy for the process with a Z boson and one parton in the final state. The fourth combines the fully differential next- to- next- to- leading order calculation of the process with no parton in the final state with next- to- next- to- leading logarithm resummation and parton showering

Evidence for the Associated Production of a Single Top Quark and a Photon in Proton-Proton Collisions at s =13 TeV

The first evidence of events consistent with the production of a single top quark in association with a photon is reported. The analysis is based on proton-proton collisions at root s = 13 TeV and recorded by the CMS experiment in 2016, corresponding to an integrated luminosity of 35.9 fb(-1). Events are selected by requiring the presence of a muon (mu), a photon (gamma), an imbalance in transverse momentum from an undetected neutrino (nu), and at least two jets (j) of which exactly one is identified as associated with the hadronization of a b quark. A multivariate discriminant based on topological and kinematic event properties is employed to separate signal from background processes. An excess above the backgroundonly hypothesis is observed, with a significance of 4.4 standard deviations. A fiducial cross section is measured for isolated photons with transverse momentum greater than 25 GeV in the central region of the detector. The measured product of the cross section and branching fraction is sigma(pp -> t gamma j) B (t -> mu nu b) = 115 +/- 17 (stat) +/- 30(syst) fb, which is consistent with the standard model prediction

Study of jet quenching with isolated-photon+jet correlations in PbPb and pp collisions at sNN=5.02 TeV

Measurements of azimuthal angle and transverse momentum (p(T)) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at root s(NN) = 5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with p(T)(gamma) > 40 GeV/c and an associated jet with p(T)(jet) > 30 GeV/c, the photon+jet azimuthal correlation and p(T) imbalance in PbPb collisions are studied as functions of collision centrality and p(T)(gamma). The results are compared to pp reference data collected at the same collision energy and to predictions from several theoretical models for parton energy loss. No evidence of broadening of the photon+jet azimuthal correlations is observed, while the ratio p(T)(jet)/p(T)(gamma) decreases significantly for PbPb data relative to the pp reference. All models considered agree within uncertainties with the data. The number of associated jets per photon with p(T)(gamma) > 80GeV/c is observed to be shifted towards lower p(T)(jet) in central PbPb collisions compared to pp collisions. (C) 2018 The Author. Published by Elsevier B.V