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Identification of events with four top quarks in data from the LHC collider using machine learning algorithms
Bulín, Vít ; Scheirich, Daniel (advisor) ; Pleskot, Vojtěch (referee)
Jet tagging is a method of analyzing accelerator collision products. It performs labeling of jets according to the flavor of quark from which they arose. The subject of the thesis is to use machine learning and deep learning algorithms to build a top-tagging neural network and to prepare this network for being used as a support mechanism for the identification of four top decay events. Our top-tagger architecture is based on the successful Transformer architecture. To achieve the final form of top-tagger several variations in architecture and several sets of hyperparameters were tried. Subsequently, the best-performing model was chosen. The result of our thesis constitutes of tested functioning top-tagger. Moreover, an optimal setting for further use in identifying four top events was found. The output of our neural network will be suitable to use as additional information to the input of more versatile classification models thus creating space for improvement of those classification models. 1
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Quark/gluon jet tagging
Jankových, Samuel ; Pleskot, Vojtěch (advisor) ; Scheirich, Daniel (referee)
Distinguishing between jets initiated by quarks and gluons is a challenging problem, yet very important for detailed studies of elementary particles and their interactions. This thesis will present a novel Deep Learning approach to this problem using a neural network architecture based on the Transformer model trained on the jet constituents. We improve the existing architectures used in different tagging tasks and show their ability to accurately distinguish between quark and gluon jets. By combining techniques from different fields of Deep Learning, we propose a Dynamically Enhanced Particle Transformer (DeParT) that can surpass the state-of-the-art results in the quark/gluon jet tagging task.
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Jet substructure at Future Circular Collider (FCC)
Petrů, Tadeáš ; Faltová, Jana (advisor) ; Scheirich, Daniel (referee)
Title: Jet substructure at Future Circular Collider (FCC) Author: Tadeáš Petrů Department: Institute of Particle and Nuclear Physics Supervisor: Mgr. Jana Faltová, Ph.D., Institute of Particle and Nuclear Physics Abstract: Future Circular Collider (FCC-hh) is a proposed next-generation hadron collider with a center-of-mass energy of 100 TeV that could be built in CERN. This collider would serve both as a powerful discovery machine and also as a precision measurements machine. One of the challenges for detectors installed at FCC-hh would be an identification of highly boosted objects that subsequently decay hadronically. Within this thesis, we will study the ability of the calorime- ter system of the FCC-hh reference detector in distinguishing two-pronged jets from highly boosted W boson decays and one-pronged jets from light quarks. We will introduce several jet substructure variables and use them as inputs for multivariate analysis (boosted decision trees). Keywords: FCC, substructure, boosted objects iii
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Study of proton-proton and heavy-ion collisions with the ATLAS experiment at the LHC
Balek, Petr ; Dolejší, Jiří (advisor) ; Scheirich, Daniel (referee) ; Šumbera, Michal (referee)
Title: Study of proton-proton and heavy-ion collisions with the ATLAS experi- ment at the LHC Author: Mgr. Petr Balek Department: Institute of Particle and Nuclear Physics Supervisor: Doc. RNDr. Jiří Dolejší, CSc. Abstract: The presented results show a suppression in a production of charged hadrons in heavy-ion collisions with respect to the production measured in proton- proton collisions. Lead-lead data at √ sNN = 2.76 TeV were recorded by the AT- LAS experiment at the LHC in 2010 and 2011 and they have a total integrated luminosity of 0.15 nb−1 , and proton-proton data at √ s = 2.76 TeV were recorded in 2011 and 2013 having an integrated luminosity of 4.2 nb−1 . The results are presented in wide transverse momentum (0.5 < pT < 150 GeV) and pseudorapid- ity (|η| < 2) ranges, and also in different centrality intervals of Pb+Pb collisions. Nuclear modification factor RAA shows a clear pT-dependence with a minimum at around 7 GeV, however above 60 GeV, it reaches a plateau with no significant pT-dependence. As a function of |η|, the RAA is flat over whole pT region. Keywords: ATLAS detector, heavy-ion collisions, charged-hadron spectra, nuclear modification factor RAA
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Development of optimal algorithms for the selection of rare semimuonic B decays in ATLAS
Scheirich, Daniel ; Doležal, Zdeněk (advisor) ; Mašík, Jiří (referee)
In this thesis we propose the trigger algorithm for the semimuonic rare B decay selection in ATLAS experiment and we study its performance using the Monte Carlo sample of b 0u+u. The cut optimisation have been performed in order to obtain the optimal cut values and the signal rate for the process was estimated. The feasibility and performance of the tag-and-probe method for the calibration of di-muon triggers is investigated, too. Eects of the systematic uncertainties of the method on the measurements of J/ polarisation and the forward-backward asymmetry of b 0u+u were studied.
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Measurement of the Λb baryon mass in the ATLAS experiment
Macko, Vladimír ; Scheirich, Daniel (advisor) ; Faltová, Jana (referee)
The mass of the Λb baryon has been studied in proton-proton collisions using experimental data from the ATLAS detector at the LHC in CERN. The mass is measured by reconstructing momenta of products in the studied decay. Decay channel Λb → J/ψ(µ+ µ− )Λ(pπ− ) is chosen for the mass reconstruction in this work. The selection criteria are applied in order to minimize background effect and, therefore, obtain the value of the mass of the Λb baryon with the lower statistical error. The systematic error is obtained from a comparison of the three statistical models describing experimental data. The result of measurement of the Λb baryon mass in the ATLAS experiment performed in this work is: mΛb = (5619.1 ± 1.0) MeV. 1
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Study of CP-violation at the Belle experiment
Červenkov, Daniel ; Doležal, Zdeněk (advisor) ; Bielčík, Jaroslav (referee) ; Scheirich, Daniel (referee)
We present a first measurement of time-dependent CP-violation in B0 → D∗∓ ρ± , where D∗∓ → D0 π. The analysis was performed using the final Belle dataset containing 772 × 106 B ¯B pairs collected at the KEKB e+ e− collider. Three D0 decay modes are analyzed, K∓ π± , K∓ π± π0 , and K∓ π± π∓ π± . Since the studied decay is a scalar → vector vector decay, three helicity configurations are present. Exploiting the helicity configura- tions via angular analysis, the time-dependent CP-violation parameters encoding 2ϕ1 +ϕ3 are obtained from the fit. 1
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Study of the rare B-meson decays with the ATLAS experiment
Biroš, Marek ; Řezníček, Pavel (advisor) ; Scheirich, Daniel (referee)
Title: Study of the rare B-meson decays with the ATLAS experiment Author: Marek Biroš Institute: Institute of Particle and Nuclear Physics Supervisor: RNDr. Pavel Řezníček, Ph.D., Institute of Particle and Nuclear Physics Abstract: The rare B0 d → K∗0 (892) μμ decay is one of the B-physics channels sensitive to Beyond Standard Model effects. The potential deviation from Standard Model predictions could be observed in the angular distribution of this decay. The work compiles several sub-tasks at the initial stage of this complex analysis: decay angles fit validation and signal event preselection. The fit functions used in the analysis are verified on generated toy Monte Carlo data. Ranges of parameters, for which are these functions positive, are established and within this parametric space, the testing of possible intrinsic fit biases is evaluated. A dependence of the fit bias with respect to the collected number of events (expected in Run 2 as well as at HL-LHC) and to the different signal-to- background ratio is studied. The second part of the thesis deals with processing of raw reconstructed data from the detector into n-tuples resulting in a more compact dataset that would be used in the final analysis. Within the process, baseline cuts are applied in order to minimize size of final datasets by reducing...
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Beta Source Tests of Semiconductor Detectors ITk for ATLAS Upgrade
Kovanda, Ondřej ; Kodyš, Peter (advisor) ; Scheirich, Daniel (referee)
Beta Source Tests of Semiconductor Detectors ITk for ATLAS Upgrade Abstract: The ATLAS experiment is due to undergo a major upgrade for the High Luminosity phase of the LHC operation. In particular, the current tracking system (ID) will be replaced by full-silicon ITk. IPNP laboratories are involved in R&D of SCT detector modules for ITk. Low-temperature β-source tests of the R0 FR 5 module prototype were the main focus of this thesis. After testing the cooling cycle, 11 threshold scans were performed on two ABC130 chips, yielding the median collected charge ranging between 2.9 ± 0.2 fC and 3.1 ± 0.2 fC for chip #6 at SNR from 16.0 ± 1.0 at 24 ◦ C to 22.7 ± 1.5 at −15 ◦ C. No trend with temperature was observed outside the error bars. The results are in accordance with previous similar measurements. Question of fitting the median collected charge in various units was adressed and equivalence of the fits was determined. The ability of IPNP laboratories to perform low-temperature β-source tests was proven.
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