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Studium potlačení jetů ve srážkách těžkých iontů na LHC pomocí detektoru ATLAS
Štefko, Pavol ; Spousta, Martin (advisor) ; Pleskot, Vojtěch (referee)
Jet production in PbPb collisions at a per-nucleon center-of-mass energy of 2.76 TeV has been studied using the ATLAS detector at the LHC. Interactions between the high- pT partons and the hot, dense medium, produced in these ultrarelativistic collisions, are expected to cause the loss of the jet energy (jet quenching). This thesis presents results of the jet analysis done on the data taken during the 2011 heavy-ion run at the LHC. Jets are reconstructed using the anti-kt jet clustering algorithm and studied as a function of collision centrality and dijet energy imbalance. With increasing centrality, dijets are observed to be increasingly asymmetric, consistent with the theory of jet quenching. The study of charged particle tracks indicates the increase of the low-pT tracks in the strongly quenched jets. 1
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Search for leptoquarks with the ATLAS experiment
Martinovicová, Gabriela ; Pleskot, Vojtěch (advisor) ; Mlynáriková, Michaela (referee)
The ATLAS experiment records data from the collisions of protons accelerated in the Large Hadron Accelerator (LHC). The LHC is a major part of the Accele- rator Complex in the European Organization for Nuclear Research (CERN). In the recorded data it is possible to find new undiscovered particles by means of data analysis. Example of such particles are leptoquarks. This bachelor thesis is based on data collected in 2015-2016 at 13 TeV centre-of-mass energy and with a total luminosity of 36.1 fb−1 . In these data, there was no indication of the exis- tence of leptoquarks, which originate from the paired production with the decay channel, where one leptocvark decays into muon and quark and the other one into neutrino and quark, and so this thesis aims to set a limit on the production cross-section for these particles. 1
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Studium kanálu J/Psi + foton v proton-protonových srážkách pomocí detektoru ATLAS na LHC
Vidláková, Zuzana ; Vrba, Václav (advisor) ; Zálešák, Jaroslav (referee)
Title: Analysis of J/Psi + photon production in proton-proton collisions on ATLAS at LHC Author: Bc. Zuzana Vidláková Department: Institute of particle and nuclear physics Supervisor: prom. fyz. Václav Vrba, CSc. (Academy of Sciences of the Czech Republic) Abstract: The subject of this thesis is physics connected to quarkonia and their studies at the ATLAS detector situated at LHC in CERN, Geneva. In this thesis, following topics are cov- ered: ATLAS detector, history of physics connected to quarkonia, production mechanisms of quarkonia, software used at CERN for data analysis and cross-section measurement of J/Psi + photon continuum. The analysis was done on behalf of the B-physics working group at ATLAS. Keywords: CERN, LHC, ATLAS, B-fyzika, quarkonia
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Studium kinematiky rozpadů top-antitopových párů v experimentu Atlas
Berta, Peter ; Kvita, Jiří (advisor) ; Soustružník, Karel (referee)
In this thesis, I deal with the measurement of the transverse momentum spectrum of the top quark produced in top-antitop pairs at the LHC at center of mass energy 7 TeV. The analysis is carried out within the ATLAS collaboration. In the single lepton decay channel, I have performed studies on the simulation which were necessary to obtain the final spectrum from real data. I describe basic event selection rules to reduce background events. I study the efficiency of top-antitop pairs reconstruction. I study the unfolding of the measured spectrum which corrects for effects caused by imperfect resolutions. At the end, I show the measured top quark transverse momentum spectrum obtained from my analysis.
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Measurement of the B0 meson lifetime at ATLAS detector
Řezníček, Pavel ; Doležal, Zdeněk (advisor) ; Cvach, Jaroslav (referee) ; Catmore, James Richard (referee)
Title: Measurement of the B0 d meson lifetime at ATLAS detector Author: Pavel Řezníček Department: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: Dr. Zdeněk Doležal Supervisor's e-mail address: Zdenek.Dolezal@mff.cuni.cz Abstract: The lifetime of B0 d mesons is determined from their decays B0 d → J/ψK∗0 reconstructed in ATLAS experiment at the LHC using pp collision data at a center-of-mass energy of 7 TeV and corresponding to integrated luminosity of 40 pb−1 . The lifetime, extracted from the simultaneous unbinned maximum likelihood mass-lifetime fit, is 1.51±0.04 (stat.)±0.04 (syst.) ps. A total number of 2750±90 (stat.) signal B0 d decays are observed in the measurement, with a fit- ted B0 d mass of 5363.7 ± 1.2 (stat.) MeV. Both the extracted B0 d meson mass and lifetime are within the determined errors consistent with the world average values. Although the achieved precision is still significantly lower than the one of the world average value, the measurement successfully tested the feasibility of the fit-method and allowed to cross-check ATLAS detector performance. Keywords: CERN, LHC, ATLAS, B-physics, B-hadron, Lifetime
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Measurement of the B0 meson lifetime at ATLAS detector
Řezníček, Pavel
Title: Measurement of the B0 d meson lifetime at ATLAS detector Author: Pavel Řezníček Department: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: Dr. Zdeněk Doležal Supervisor's e-mail address: Zdenek.Dolezal@mff.cuni.cz Abstract: The lifetime of B0 d mesons is determined from their decays B0 d → J/ψK∗0 reconstructed in ATLAS experiment at the LHC using pp collision data at a center-of-mass energy of 7 TeV and corresponding to integrated luminosity of 40 pb−1 . The lifetime, extracted from the simultaneous unbinned maximum likelihood mass-lifetime fit, is 1.51±0.04 (stat.)±0.04 (syst.) ps. A total number of 2750±90 (stat.) signal B0 d decays are observed in the measurement, with a fit- ted B0 d mass of 5363.7 ± 1.2 (stat.) MeV. Both the extracted B0 d meson mass and lifetime are within the determined errors consistent with the world average values. Although the achieved precision is still significantly lower than the one of the world average value, the measurement successfully tested the feasibility of the fit-method and allowed to cross-check ATLAS detector performance. Keywords: CERN, LHC, ATLAS, B-physics, B-hadron, Lifetime
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Study of electromagnetic processes in ultra-peripheral collisions of heavy-ions at the Large Hadron Collider
Váňa, Pavel ; Spousta, Martin (advisor) ; Mlynáriková, Michaela (referee)
This thesis contains a study of electromagnetic processes created in heavy-ion collisi- ons during interaction of electromagnetic fields of nuclei. During these collisions, dimuon pairs are produced via γγ → µ+ µ− processes. Dimuon pairs then penetrate quark gluon plasma created in heavy-ion collisions and their kinematics may be altered by the presence of the plasma. The aim of this thesis is to develop simple geometric model that is then im- plemented and a program for measuring the path length of products of electromagnetic processes is delivered. The simulation of centrality dependent acoplanarity broadening is performed. Centrality dependent acoplanarity broadening of dimuon pairs produced in γγ → µ+ µ− processes was previously measured by the ATLAS detector at the LHC in Pb+Pb collisions at √ sNN = 5.02TeV. It was shown that model can reproduce the dis- tribution of acoplanarity measured by ATLAS for α > 2.10−3 rad when the quadratic configuration of path-length dependence of acoplanarity broadening is used. On the con- trary, measurement of acoplanarity distribution for α < 2.10−3 rad cannot be reproduced by the model. 1
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Estimation of background for final states including tau leptons with the ATLAS experiment
Nocarová, Marta ; Pleskot, Vojtěch (advisor) ; Mlynáriková, Michaela (referee)
Processes with tau leptons in a final state are essential in many experi- ments studying products of proton collisions. Tau lepton most often decays hadronically; therefore jets misidentified as tau leptons can be a source of a significant part of the background of these events. A part of phase space where most reconstructed taus are misidentified jets is chosen. This part of phase space can be events with Z boson decaying into two muons. These events were studied, and distributions of several variables were compared with Monte Carlo simulation. A second part of the thesis presents studies based on a subsample of these events, consisting of events with an addi- tional jet passing specific loose tau lepton selection criteria. A data-driven method for estimating this type of background, fake factor, was studied on these events. 1
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Study of hard processes at the LHC
Zívr, Vojtěch ; Spousta, Martin (advisor) ; Faltová, Jana (referee)
There were studied PbPb collisions at a per-nucelon center-of-mass en- ergy of 2760 GeV. Such collisions produce quark-gluon plasma and jets. Specifically, the properties of events dominated by gluon and quark jets were studied. The properties were multiplicity, pseudorapidity and trans- verse momentum. The study found greater multiplicity in events dominated by gluon jets, compared to quark jets. Furthermore, it was found that more electrically charged particles are formed than their electrically neutral part- ners. Examination of pseudorapidity revealed that particles in jets have lower pseudorapidity compared to background. In contrast, no statistically significant differences were observed in the distribution of transverse mo- mentum depending on the type of hadron. 1
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Search for leptoquarks with the ATLAS experiment
Martinovicová, Gabriela ; Pleskot, Vojtěch (advisor) ; Mlynáriková, Michaela (referee)
The ATLAS experiment records data from the collisions of protons accelerated in the Large Hadron Accelerator (LHC). The LHC is a major part of the Accele- rator Complex in the European Organization for Nuclear Research (CERN). In the recorded data it is possible to find new undiscovered particles by means of data analysis. Example of such particles are leptoquarks. This bachelor thesis is based on data collected in 2015-2016 at 13 TeV centre-of-mass energy and with a total luminosity of 36.1 fb−1 . In these data, there was no indication of the exis- tence of leptoquarks, which originate from the paired production with the decay channel, where one leptocvark decays into muon and quark and the other one into neutrino and quark, and so this thesis aims to set a limit on the production cross-section for these particles. 1
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