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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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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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Studium rozpadů Higgsova bosonu na páry tau leptonů s použitím detektoru ATLAS na LHC
Kello, Tomáš ; Scheirich, Daniel (advisor) ; Řezníček, Pavel (referee)
The analysis of the Higgs boson decay into the pairs of tau leptons H → ττ is presented. In the scope of this thesis, only the tau leptons decaying purely lep- tonically are considered. This analysis is performed using data recorded from the proton-proton collisions at a center-of-mass energy √ s = 13 TeV by the ATLAS detector at the Large Hadron Collider and correspond to the integrated lumi- nosity of 36.1 fb−1 . The Boosted Decision Trees (BDT) multivariate technique was used in order to provide a classification of events. Datasets considered in this analysis consisted of the triggered, reconstructed and calibrated events. In addition, events had to pass the pre-selection criteria and were separated into four categories. Our main contribution to this analysis is based on developing and incorporating techniques used in the process of BDT training and evaluation. The performed analysis presented in this thesis is blinded. Therefore, the Monte Carlo simulation was used instead of real data in the Maximum Likelihood Fit in order to determine the expected significance. For the H → ττ leptonic channel, the expected signal significance was measured to be 1.16 σ. 1
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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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Monte Carlo Simulations of the Tile Calorimeter and Measurement of the Z→ττ Cross Section with the ATLAS Detector
Nováková, Jana ; Davídek, Tomáš (advisor) ; Trávníček, Petr (referee) ; Taševský, Marek (referee)
Title: Monte Carlo Simulations of the Tile Calorimeter and Measurement of the Z → ττ Cross Section with the ATLAS Detector Author: Mgr. Jana Nováková Department: Institute of Particle and Nuclear Physics (IPNP) Supervisor: RNDr. Tomáš Davídek, PhD., IPNP Supervisor's e-mail address: davidek@ipnp.troja.mff.cuni.cz Abstract: The Monte Carlo simulations of the Tile calorimeter in the ATLAS experiment at the LHC, especially the electronic noise and multiple interactions (co-called pile-up), are discussed in the thesis. A good agreement in the cell energy distribution between data and Monte Carlo simulations is found. The cross section measurement of Z → ττ events with the ττ invariant mass between 66 and 116 GeV with the ATLAS experiment is described in the next part of the thesis. Data samples collected during 2011 corresponding to the integrated luminosity of 1.34 - 1.55 fb−1 are used for the analysis. The measurements are performed in three different final states depending on the decay mode of the τ leptons. The measurement in the channel with one τ lepton decaying leptonically into the electron + neutrinos (schematically τ → e + νe + ντ ) and the other one hadronically (schematically τ → hadrons + ντ ), especially the calculation of the nominal cross section and the evaluation of the systematic...
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