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Calibration of the Belle II detector
Šitina, Samuel ; Žlebčík, Radek (advisor) ; Gruberová, Zuzana (referee)
This thesis proposes an improved method for calibration of the Belle II detector by introducing an algorithm that determines the optimal length of the calibration intervals. The calibrated quantity is the centre-of-mass energy of the e+ e- collisions and is determined from the invariant mass of e+ e- → μ+ μ- events. For a given number of the calibration intervals, a method to find optimal positions of the interval boundaries is developed. Furthermore, a cross-validation technique is applied to choose the total number of intervals such that the data are not overfitted or underfitted. The performance of the algorithm is tested on the data from the Belle II experiment and the results together with further possible improvements are discussed.
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Exploring jet calibration with machine learning techniques
Novotný, Patrik ; Rybář, Martin (advisor) ; Žlebčík, Radek (referee)
Title: Exploring jet calibration with machine learning techniques Author: Patrik Novotný Institute: Institute of Particle and Nuclear Physics Supervisor: Mgr. Martin Rybář, Ph.D., Institute of Particle and Nuclear Physics Abstract: Jets, collimated sprays of particles, are considered to be a perfect probe of the matter created at heavy-ion collisions. The work explores the possibility of using machine learning techniques to improve the overall calibration of jet energy scale and its resolution for ATLAS experiment calorimeters, which are used in the research of lead nucleus collisions. First, the current performance of jet reconstruction quantified by mean response and energy resolution dependence on the value of transverse momentum, pseudorapidity, and centrality of collisions is shown. It is further discussed that the current calibration does not take into account whether the jets are induced by a quark or gluon. Subsequently, four variables are selected, which might be used to distinguish between these two groups of jets. The dependence of the response on those quantities and on centrality is further studied. The last part describes the process of the preparation of a training data set, set up of the neural network, and the analysis of it using tools provided by the MultiLayerPerceptron library of the...
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Study of the time-dependent CP violation at the Belle II experiment
Kapitánová, Lucia ; Žlebčík, Radek (advisor) ; Pleskot, Vojtěch (referee)
This thesis is devoted to studies of the proper decay-time resolution function and particle decay vertex reconstruction tools, their applicability and role in the studies of time-dependent CP violation at the Belle II experiment. A positive effect of beam spot constraints and new beam spot calibration on the vertex reconstruction precision is seen via MC/data comparison. The core part of the work focuses on studying universality of the time resolution function across nine different neutral and charged B-meson decay channels. The possibility to use a single form of this function for all studied channels is demon- strated and supported by the consistency between the lifetime values used for simulation and obtained as results of the decay time difference fit. 1
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Diffractive Dijet Production with Leading Proton in ep Collisions at HERA.
Žlebčík, Radek ; Valkárová, Alice (advisor) ; Chýla, Jiří (referee) ; Levonian, Sergey (referee)
The cross section of the diffractive process e+p → e+Xp is measured at a centre-of-mass energies of 319 GeV, where the system X contains at least two jets and the leading final state proton p is detected in the H1 Very Forward Proton Spectrometer. The measurement is performed in photoproduction defined by photon virtualities Q2 < 2 GeV2 and in deep-inelastic scattering with 4 GeV2 < Q2 < 80 GeV2 . The results are compared to next-to-leading order QCD calculations based on diffractive parton distribution functions as extracted from measurements of inclusive cross sections in diffractive deep- inelastic scattering. A collinear QCD factorization theorem is tested against the measured cross sections and their ratios. 1
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