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Precision measurement of neutrino oscillations parameters
Dohnal, Tadeáš ; Leitner, Rupert (advisor)
The Daya Bay Reactor Neutrino Experiment, located in Southeast China, was de- signed to measure short baseline oscillation of electron antineutrinos originating from six 2.9 GWth nuclear reactors. In 2012, it discovered the nonzero value of the θ13 mixing angle and currently provides the world's most precise measurement of this neutrino os- cillation parameter. The goal of this thesis is to check the performance of the detector nonuniformity correction used by the Daya Bay experiment and then design a new im- proved version. For that purpose, the Daya Bay experiment is introduced including the procedure of the event reconstruction. Several types of signals are then studied in detail and later they are used to scrutinize the performance of the nonuniformity correction. Several issues are identified, most significantly an absence of radial dependence in the azimuthal part of the correction and inability to deal with dead photomultipliers. A new improved version of the correction that addresses these issues is then designed with the main goal to improve the precision of Daya Bay neutrino oscillation analyses, especially ongoing one which uses neutron capture on hydrogen. The impact of the new improved correction on said analyses is also assessed. 1
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Precision measurement of neutrino oscillations parameters
Dohnal, Tadeáš ; Leitner, Rupert (advisor) ; Stríženec, Pavol (referee) ; Zálešák, Jaroslav (referee)
The Daya Bay Reactor Neutrino Experiment, located in Southeast China, was de- signed to measure short baseline oscillation of electron antineutrinos originating from six 2.9 GWth nuclear reactors. In 2012, it discovered the nonzero value of the θ13 mixing angle and currently provides the world's most precise measurement of this neutrino os- cillation parameter. The goal of this thesis is to check the performance of the detector nonuniformity correction used by the Daya Bay experiment and then design a new im- proved version. For that purpose, the Daya Bay experiment is introduced including the procedure of the event reconstruction. Several types of signals are then studied in detail and later they are used to scrutinize the performance of the nonuniformity correction. Several issues are identified, most significantly an absence of radial dependence in the azimuthal part of the correction and inability to deal with dead photomultipliers. A new improved version of the correction that addresses these issues is then designed with the main goal to improve the precision of Daya Bay neutrino oscillation analyses, especially ongoing one which uses neutron capture on hydrogen. The impact of the new improved correction on said analyses is also assessed. 1
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Time resolution of TileCal and searches for heavy metastable particles
Pagáčová, Martina ; Leitner, Rupert (advisor) ; Němeček, Stanislav (referee)
Title: Time resolution of TileCal and searches for heavy metastable parti- cles Author: Martina Pagáčová Department: Institute of Particle and Nuclear Physics Supervisor: Doc. RNDr. Rupert Leitner, DrSc. Supervisor's e-mail address: Rupert.Leitner@cern.ch Abstract: In the present work, the timing of the ATLAS TileCal is stud- ied using the single hadron collision data. The time resolution and also the mean time response depend on the energy deposited in a given cell. The results are compared to the previous analysis with jets and muons. Precise time-of-flight measurement using TileCal can be used to identify the heavy long-lived particles predicted by the models of physics beyond the standard model. Their mass can be reconstructed by combining with the momentum measurement in the ATLAS inner detector. Finally, the mass resolution of an exotic particle with mass M = 600 GeV is estimated. Keywords: ATLAS experiment, TileCal, time resolution, stable massive particles
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Zkoumání vlastností Higgsova bosonu v experimentu ATLAS
Mlynáriková, Michaela ; Leitner, Rupert (advisor) ; Kampf, Karol (referee)
The Standard Model of elementary particles (SM) predicts the existence of a neutral scalar Higgs boson. However, there are also extensions of the SM (such as the MSSM) in which a number of Higgs bosons is predicted. Especially the additional presence of pseudoscalar and charged Higgs bosons represents one of the crucial differences between the SM and its exten- sions. This work develops a method for determination of the spin and parity of the Higgs boson in several H → ττ decays, namely: H→ τ+ τ− → (h+ ντ )(h− ¯ντ ), H→ τ+ τ− → ( + ντ ¯ν )(π− ¯ντ ) and H→ τ+ τ− → ( + ντ ¯ν )( − ¯ντ ν ), where h denotes π or ρ meson. The method is based on the angular and energy correlations of charged final products from the decays mentioned above. Additionally, the work studies the possibility of signal (Higgs boson decay) and background (Z → ττ decay) discrimination, when one considers a decaying boson with spin 1. All calcula- tions are done in the leading order of perturbation theory. 1
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Investigation of properties of the top quark with the ATLAS experiment at LHC
Berta, Peter ; Leitner, Rupert (advisor) ; Bielčíková, Jana (referee) ; Kepka, Oldřich (referee)
This thesis presents the measurement of the differential cross section of the top-antitop pair production in proton-proton collisions at center-of-mass energy of 8 TeV at the ATLAS experiment. The measurement is performed for top-antitop events in the single lepton decay channel in the boosted topol- ogy. The measured differential cross section is expressed as a function of the top quark transverse momentum at particle level and at parton level. The mea- sured distributions are compatible with the theoretical predictions of the Standard Model. The experimental techniques used in this measurement are discussed with emphasis on the jet reconstruction and on the identification of jets originating from b-quark fragmentation. The jet reconstruction is influenced by simultane- ous proton-proton collisions (pileup), and the mitigation of these pileup effects is studied. A novel pileup subtraction technique for jets is proposed using an ex- tension of the methods currently being employed by the LHC experiments. The new method has a good performance in removing the pileup contributions at the level of jet constituents. 1
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Decay of light Higgs boson to pair of intermediate bosons W
Mlynáriková, Michaela ; Leitner, Rupert (advisor) ; Kampf, Karol (referee)
In this thesis the decay of the Higgs boson H → W+ W− → + ν − ¯ν is studied. The main goal of this work is to investigate the correlations between masses of the W bosons and the correlations between the angular distributions of leptons. The Higgs boson mass is considered to be mH ≤ 2mW , in which case the Higgs boson decays into a pair of W bosons, where one is on its mass shell mW while the other has lower mass. We calculate the most probable masses of W bosons using first the trivial and then the complete matrix elements, respectively. For the Higgs boson mass of mH = 125 GeV the angular correlation of final state leptons is also studied using the most probable W masses obtained in the first part of the study. 1
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