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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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Studium procesů s účastí kvarku b v experimentu Belle
Červenkov, Daniel ; Doležal, Zdeněk (advisor) ; Kepka, Oldřich (referee)
Title: Study of b-quark processes in the Belle experiment Author: Daniel Červenkov Department: Institute of Particle and Nuclear Physics Supervisor: Zdeněk Doležal Co-Supervisor: Karim Trabelsi Abstract: A study regarding the plausability of using the B0 → D∗ ρ± decay channel and the data set of the Belle experiment to measure sin(2φ1+φ3) has been carried out. Two fitters have been created. A time-independent one, which ex- hibits high stability and reports gratifying fit uncertainties, and a time-dependent one. During the testing of the latter we have discovered an EvtGen flaw and pro- posed a temporary workaround. Nevertheless, the time-dependent fitter fails to recover the correct values. More work will be needed to reach conclusive results. Keywords: B meson, CP violation, angular analysis, time-dependent, fitter
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QCD and Diffraction in the ATLAS Experiment at the LHC
Kepka, Oldřich ; Kupčo, Alexander (advisor) ; Favart, Laurent (referee) ; Stirling, W.J. (referee)
This thesis is devoted to study the hard diffractive and exclusive events at the experiment ATLAS. Right after the start-up of a new proton accelerator LHC in CERN they will be identied using the rapidity gap method. We therefore developed an alternative denition of the observed energy in the ATLAS calorimeter to identify diffractive and exclusive events. During the high luminosity operation of the accelerator, forward detectors (AFP) recently proposed to be installed far from the interaction point approaching the beam at few millimeters will allow to tag the intact scattered protons in these events unambiguously. The simplest exclusive production is due to the exchange of two photons. We implemented twophoton exchanges in FPMC generator and analyzed the two-photon production of W and Z-pairs decaying leptonically to calculate sensitivities on triple and quartic anomalous gauge couplings of electroweak boson to photons. The obtained results are remarkable mainly for the quartic couplings. Their current limits can be improved by almost two orders of magnitude with early data and by four orders of magnitude using large luminosity and AFP detectors. In addition, we used two-photon dimuon events to determine the time needed to align one of the AFP stations with respect to beam to a desired precision. Another...
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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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Analysis of Diffractive Open Charm Photoproduction with a Leading Proton at HERA
Jansová, Markéta ; Černý, Karel (advisor) ; Kepka, Oldřich (referee)
The diffractive open charm production is studied using data from 2006-2007, when the leading proton measurement by H1 Very Forward Proton Spectrometer was provided. The charm production is tagged by the decay products of D∗ meson. The cross section of e+ p → e+ D∗ X p in photoproduction regime defined by the value of virtuality Q2 < 2 GeV is determined and corrected for the detector effects. The diffractive D∗ meson photoproduction cross section is compared with the hadron level MC Rapgap prediction based on diffractive parton distribution functions extracted from inclusive ep DIS measurements. Measurement of leading proton provides a unique opportunity to investigate the response of forward detectors for the diffractive events. Using such events, the performance of the large rapidity gap selection is examined.
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Studium procesů s účastí kvarku b v experimentu Belle
Červenkov, Daniel ; Doležal, Zdeněk (advisor) ; Kepka, Oldřich (referee)
Title: Study of b-quark processes in the Belle experiment Author: Daniel Červenkov Department: Institute of Particle and Nuclear Physics Supervisor: Zdeněk Doležal Co-Supervisor: Karim Trabelsi Abstract: A study regarding the plausability of using the B0 → D∗ ρ± decay channel and the data set of the Belle experiment to measure sin(2φ1+φ3) has been carried out. Two fitters have been created. A time-independent one, which ex- hibits high stability and reports gratifying fit uncertainties, and a time-dependent one. During the testing of the latter we have discovered an EvtGen flaw and pro- posed a temporary workaround. Nevertheless, the time-dependent fitter fails to recover the correct values. More work will be needed to reach conclusive results. Keywords: B meson, CP violation, angular analysis, time-dependent, fitter
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QCD and Diffraction in the ATLAS Experiment at the LHC
Kepka, Oldřich ; Kupčo, Alexander (advisor) ; Favart, Laurent (referee) ; Stirling, W.J. (referee)
This thesis is devoted to study the hard diffractive and exclusive events at the experiment ATLAS. Right after the start-up of a new proton accelerator LHC in CERN they will be identied using the rapidity gap method. We therefore developed an alternative denition of the observed energy in the ATLAS calorimeter to identify diffractive and exclusive events. During the high luminosity operation of the accelerator, forward detectors (AFP) recently proposed to be installed far from the interaction point approaching the beam at few millimeters will allow to tag the intact scattered protons in these events unambiguously. The simplest exclusive production is due to the exchange of two photons. We implemented twophoton exchanges in FPMC generator and analyzed the two-photon production of W and Z-pairs decaying leptonically to calculate sensitivities on triple and quartic anomalous gauge couplings of electroweak boson to photons. The obtained results are remarkable mainly for the quartic couplings. Their current limits can be improved by almost two orders of magnitude with early data and by four orders of magnitude using large luminosity and AFP detectors. In addition, we used two-photon dimuon events to determine the time needed to align one of the AFP stations with respect to beam to a desired precision. Another...
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The QCD analysis of multijet events in proton-antiproton collisions at the Tevatron
Kepka, Oldřich ; Kupčo, Alexander (advisor) ; Žáček, Josef (referee)
The recent developments in theoretical calculations (code NLOJET++) allow us to evaluate the 3-jet observables at the next-to-leading order precision. In this diploma thesis we investigate the potential of using 3-jet observables for the measurement of strong coupling s at hadron colliders. First, we analyze the inclusive jet cross section measured by DO Collaboration, determine s and demonstrate its running in a similar way as was previously done by CDF Collaboration. In the second part of the thesis, we analyze the DO measurement of dijet azimuthal decorrelations. With this choice of 3-jet observable we were able to achieve a better precision of s than in the previous s measurements based on the inclusive jet production.
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