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Studies of Higgs boson in its decay to a pair of tau-leptons and search for excited tau-lepton with the ATLAS detector
Mihule, Kristina ; Davídek, Tomáš (advisor) ; Kvita, Jiří (referee) ; Lysák, Roman (referee)
The Standard Model (SM) describes known elementary particles and their interactions. The ATLAS experiment is located at the Large Hadron Collider (LHC) in CERN (Geneva). The ATLAS detector measures data from proton- proton collisions at high centre-of-mass energy. The collected data allow physi- cists to precisely study SM and look for evidence of particles beyond the Stan- dard Model. The presented thesis describes the analysis of Higgs boson decay to a pair of tau-leptons. The measurement of the Higgs boson production cross section is based on the data set collected by the ATLAS detector in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV in the years 2015-18 (so-called Run 2). This dissertation presents the update of the algorithm of Higgs boson mass reconstruction for the Run 2 ATLAS conditions. The evaluation of fake tau-lepton background is also discussed. Further, this dissertation is dedicated to the search for excited tau-leptons in the Run 2 ATLAS data set. Contact interaction of the excited tau-leptons is assumed, which would occur if fermions were composite rather than elemen- tary. The analysed ATLAS data from pp collisions in Run 2 set do not contain signatures of excited tau-leptons production. Within the considered model with the compositeness scale Λ = 10 TeV, the upper...
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Time calibration of the ATLAS Tile Calorimeter
Divíšek, Martin ; Davídek, Tomáš (advisor) ; Faltová, Jana (referee)
Following the end of the maintenance period for the ATLAS detector in LHC, CERN, a series of calibrations have to be performed to ensure the quality of measured data. This thesis details the work done on time calibrations of the Tile Hadronic Calorimeter. The Tile Calorimeter uses multiple time calibration methods; these include calibration via laser (a precise light input sent to the detector's photomultipliers), and splash events analysis (measuring the overall response to high-energy particles traversing the length of the calorimeter). Several available sets of laser and splash data were analysed to determine necessary adjustments to the internal electronics and appropriate software going forward. As of April 2022, we have been able to calibrate roughly two thirds of the calorimeter, and will continue calibration once we can acquire additional data. 1
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Time calibration and resolution of the hadronic Tile Calorimeter
Krejčíková, Martina ; Davídek, Tomáš (advisor) ; Spousta, Martin (referee)
The thesis deals with Tilecal hadron calorimeter, which is part of the ATLAS detector at the LHC at CERN. Main area of interest is a time calibration of the detector, which is necessary to accurately determine the energy especially of jets produced as a result of precipitation collisions of protons. Based on obtained experimental data from 2011 thoroughly explored the relationships between the time of arrival of the particles into the cells of the detector and their energies, or the distance from the given objects. By describing the time calibration, one can correct originally obtained time constants. Description and resolution of time jumps in timing of channels are part of the thesis, corrections of identified examples are included. Powered by TCPDF (www.tcpdf.org)
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Study of B-meson decays in the Belle experiment
Krištof, Michal ; Doležal, Zdeněk (advisor) ; Davídek, Tomáš (referee)
In the thesis we study the decay of B0 meson to D∗ s and ρ mesons. The thesis explains the methods and approaches to data analysis in so-called B-factories, simmilar to the KEKB accelerator. The aim of this thesis is to calculate the branching fraction of this decay to further improve the previously measured branching ratio at BaBar experiment with additional data gained from an ex- periment with higher integrated luminosity. This thesis's prospect is not only broadening our knowledge of branching fractions of B0 meson decays, but also it is a starting point for further analysis with the goal of broadening our knowl- edge of CP symmetry violation in the Standard Model by measuring angles of the Unitary Triangle. 1
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Studium rekonstrukce rozpadu Higgs -> τ τ
Nováková, Jana ; Davídek, Tomáš (advisor) ; Dolejší, Jiří (referee)
Two independent methods of the Higgs boson mass reconstruction in the channel H are studied and compared in this thesis. The Higgs boson mass is usually reconstructed by means of a collinear approximation which is based on the measurement of missing energy and visible parts of tau leptons. Unknown momenta of neutrinos originating in the tau leptons decays have to be estimated. The mass peak is reconstructed as an invariant mass of the two tau leptons system. An alternative method, so-called decay length method, based on the tau lepton range measurement is studied in this paper. The secondary vertex reconstruction is the basic issue for this method as opposed to the energy measurement and calibration which are of crucial importance for the collinear approximation. The decay length method is not expected to give as precise results as the collinear approximation. However, it can be used as an independent test of the results of the collinear method.
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Úhlové korelace v rozpadech Higgsova bosonu
Pleskot, Vojtěch ; Davídek, Tomáš (advisor) ; Dolejší, Jiří (referee)
The Standard Model predicts existence of one Higgs boson with combined parity CP = +1. In MSSM there exist Higgs boson with CP = −1 in addition. The work develops one method of Higgs boson CP determination on the basis of angular correlations of pions and ρ-mesons born in cascade decay H/A → τ− τ+ → ρ− /π− ντ ρ+ /π+ ¯ντ . The calculations are done in the leading order of perturbation theory. Further, the possibility of signal (Higgs boson decay) and background (Z boson decay) differentiation is studied. The processes in question are simulated using Monte Carlo generators Pythia and Tauola. Simulation outputs are compared with calculated theoretical results. 1
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Study of cosmic muons in Tile calorimeter
Slovák, Radim ; Davídek, Tomáš (advisor) ; Drásal, Zbyněk (referee)
Main goal of this thesis is to learn about detector ATLAS, mainly about his hadron calorimeter Tile Calorimeter. Next step is get knowledge about processing date with program ROOT. It is necessary to test and monitor detector for example by muons from cosmic rays before his initiation. We analysed real experimental date from single module of Tile Calorimeter here. We found out signal-to-noise ratio. Then we separed out signal and noise and we found cells which muons flew through.
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Measurement of the top quark properties
Schovancová, Jaroslava ; Chudoba, Jiří (advisor) ; Davídek, Tomáš (referee) ; Filipčič, Andrej (referee)
Title: Measurement of the top quark properties Author: Mgr. Jaroslava Schovancová Department: Institute of Physics, Academy of Sciences of the Czech Re- public Supervisor: RNDr. Jiří Chudoba, Ph.D., Institute of Physics, Academy of Sciences of the Czech Republic Abstract: This Thesis presents the ATLAS experiment measurement of the top quark differential cross-section as a function of pT, mass and rapidity of the t¯t system. A sample of approx. 4.7 fb−1 of the 2011 pp collision data at the center-of-mass energy of 7 TeV was analyzed. The differential spectra shapes in the t¯t system are consistent with the Standard Model and reason- ably described by the event generators. Several activities in the scope of ATLAS Distributed Computing are pre- sented, particularly in the area of operations, monitoring, automation, and development of the PanDA Workload Management System. Such activities aim to improve efficiency and facilitate the use of distributed computing re- sources and therefore contribute in supporting the ATLAS Physics Program. Keywords: ATLAS, top quark, differential cross-section, missing transverse energy, ATLAS Distributed Computing
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