Global ETD Search

1	Rekonstrukce řídkého rozpadu K00(e4) na NA62 / NA62 data reconstruction of rare kaon decay K00(e4) Zamkovský, Michal January 2014 (has links) The thesis describes the study of the rare charged kaon decay K00 e4 on the NA62 experiment at CERN. This decay is interesting from the chiral perturbation theory point of view. In this work the data from 2007 recorded on NA62 ex- perimental setup were analyzed. The measurement of branching ratio for this process normalized to K00 3π decay has been performed. Also the form factor measurement has been done and the cusp singularity has been observed. 1
2	Některé aspekty QCD při nízkých energiích v éře přesných měření / Some aspects of low-energy QCD at the precision frontier Husek, Tomáš January 2017 (has links) Title: Some aspects of low-energy QCD at the precision frontier Author: Tomáš Husek Department/Institute: Institute of Particle and Nuclear Physics Supervisor of the doctoral thesis: doc. RNDr. Karol Kampf, Ph.D. Abstract: This thesis concentrates on some low-energy aspects of QCD, namely on those which are connected to the electromagnetic decays of lightest neutral pseudoscalar mesons. Calculations of radiative corrections to neutral pion decays (the Dalitz decay and the rare decay) and a novel model for the pion electro- magnetic transition form factor are subjects discussed in the attached papers, which this work is based on. The associated theoretical aspects including Chiral Perturbation Theory or the large-Nc limit are introduced. We also discuss the complications which arise when the calculations of radiative corrections for η(′) Dalitz decays are performed. Some details about the collaboration with experi- ments which incorporate the calculation of the published corrections are provided. Last but not least, some techniques related to loop integrals are shown. Keywords: Chiral Perturbation Theory, large-Nc limit, radiative corrections, pion electromagnetic transition form factor 1
3	Dvousmyčkové chirální korekce k rozpadu neutrálního pionu na elektron-pozitronový pár / Two-loop chiral corrections to the neutral pion decay to electron-positron pair Farkaš, Kristián January 2019 (has links) This thesis is devoted to the rare decay π0 → e+ e− . We firstly introduce all theoretical knowledge necessary for the description of the vertices used in this work. Subsequently, we introduce three two-loop chiral Feynman diagrams, which are of order O(α2 p4 ). These diagrams are firstly decomposed to Master integrals by Laporta algorithm. After that, we calculate each Master integral individually by the differential equation technique. We also focus on the renormalization of the process. Since we are working with the effective field theory, finite corrections χ from counterterm diagrams naturally appear. With use of the calculations listed in this thesis, the determination of the parameter χR could be further improved taking into account the whole two-loop correction. 1
4	Probing Electroweak Gauge Boson Scattering with the ATLAS Detector at the Large Hadron Collider Anger, Philipp 07 October 2014 (has links) (PDF) Electroweak gauge bosons as central components of the Standard Model of particle physics are well understood theoretically and have been studied with high precision at past and present collider experiments. The electroweak theory predicts the existence of a scattering process of these particles consisting of contributions from triple and quartic bosonic couplings as well as Higgs boson mediated interactions. These contributions are not separable in a gauge invariant way and are only unitarized in the case of a Higgs boson as it is described by the Standard Model. The process is tied to the electroweak symmetry breaking which introduces the longitudinal modes for the massive electroweak gauge bosons. A study of this interaction is also a direct verification of the local gauge symmetry as one of the fundamental axioms of the Standard Model. With the start of the Large Hadron Collider and after collecting proton-proton collision data with an integrated luminosity of 20.3/fb at a center-of-mass energy of 8 TeV with the ATLAS detector, first-ever evidence for this process could be achieved in the context of this work. A study of leptonically decaying WWjj, same-electric-charge diboson production in association with two jets resulted in an observation of the electroweak WWjj production with same electric charge of the W bosons, inseparably comprising WW->WW electroweak gauge boson scattering contributions, with a significance of 3.6 standard deviations. The measured production cross section is in agreement with the Standard Model prediction. In the course of a study for leptonically decaying WZ productions, methods for background estimation, the extraction of systematic uncertainties and cross section measurements were developed. They were extended and applied to the WZjj final state whereof the purely electroweakly mediated contribution is intrinsically tied to the scattering of all Standard Model electroweak gauge bosons: Wγ->WZ and WZ->WZ. Three charged leptons and a neutrino from the decay of the final state bosons allow inferences about the scattering process. A distinct signature is provided by the two accompanying tagging jets as remnants of the incoming quarks radiating the initial electroweak gauge bosons. The cross section of the electroweak WZjj production was measured to σ(fiducial, observed) = (0.63 +0.32 -0.28 (stat.) +0.41 -0.24 (syst.)) fb and was found to be consistent with the Standard Model prediction at next-to-leading order in perturbative quantum chromodynamics, σ(fiducial, theory) = (0.31 +0.03 -0.05) fb. Unfolded differential cross sections of kinematic variables sensitive to models of new physics were derived. Anomalous quartic electroweak gauge couplings are introduced as dimensionless coupling parameters of additional operators within an effective field theory approach. Constraints on the parameters of operators with dimension eight were set employing a unitarization prescription based on form factors. CERN LHC ATLAS 2014 Standardmodell Teilchenphysik Elementarteilchenphysik VBS Eichboson-Streuung Vektorboson-Streuung Vektor-Boson-Streuung aQGC aqgc anomale Eichkopplung anomale Vierer-Eichboson-Kopplung Effektive Lagrangedichte Vierer-Vertex Vierer-Eichboson-Vertex Higgs WZ-Endzustand Sherpa VBFNLO Whizard K-Matrix Form-Faktor Formfaktor Unitarisierung Boson CERN LHC ATLAS 2014 Standard Model Particle Physics VBS Vector Boson Scattering Vector-Boson-Scattering Vector-Boson Scattering Gauge Boson Scattering Electroweak Gauge Boson Scattering aQGC aqgc Anomalous Quartic Gauge Boson Coupling Anomalous Gauge Boson Coupling Effective Lagrangian Quartic Vertex Quartic Gauge Boson Vertex Higgs WZ Final State Sherpa VBFNLO Whizard K-Matrix Form-Factor Unitarization Unitarisation Boson ddc:530 rvk:UO 6420 CERN LHC 2014 Elementarteilchenphysik Boson
5	Probing Electroweak Gauge Boson Scattering with the ATLAS Detector at the Large Hadron Collider Anger, Philipp 01 September 2014 (has links) Electroweak gauge bosons as central components of the Standard Model of particle physics are well understood theoretically and have been studied with high precision at past and present collider experiments. The electroweak theory predicts the existence of a scattering process of these particles consisting of contributions from triple and quartic bosonic couplings as well as Higgs boson mediated interactions. These contributions are not separable in a gauge invariant way and are only unitarized in the case of a Higgs boson as it is described by the Standard Model. The process is tied to the electroweak symmetry breaking which introduces the longitudinal modes for the massive electroweak gauge bosons. A study of this interaction is also a direct verification of the local gauge symmetry as one of the fundamental axioms of the Standard Model. With the start of the Large Hadron Collider and after collecting proton-proton collision data with an integrated luminosity of 20.3/fb at a center-of-mass energy of 8 TeV with the ATLAS detector, first-ever evidence for this process could be achieved in the context of this work. A study of leptonically decaying WWjj, same-electric-charge diboson production in association with two jets resulted in an observation of the electroweak WWjj production with same electric charge of the W bosons, inseparably comprising WW->WW electroweak gauge boson scattering contributions, with a significance of 3.6 standard deviations. The measured production cross section is in agreement with the Standard Model prediction. In the course of a study for leptonically decaying WZ productions, methods for background estimation, the extraction of systematic uncertainties and cross section measurements were developed. They were extended and applied to the WZjj final state whereof the purely electroweakly mediated contribution is intrinsically tied to the scattering of all Standard Model electroweak gauge bosons: Wγ->WZ and WZ->WZ. Three charged leptons and a neutrino from the decay of the final state bosons allow inferences about the scattering process. A distinct signature is provided by the two accompanying tagging jets as remnants of the incoming quarks radiating the initial electroweak gauge bosons. The cross section of the electroweak WZjj production was measured to σ(fiducial, observed) = (0.63 +0.32 -0.28 (stat.) +0.41 -0.24 (syst.)) fb and was found to be consistent with the Standard Model prediction at next-to-leading order in perturbative quantum chromodynamics, σ(fiducial, theory) = (0.31 +0.03 -0.05) fb. Unfolded differential cross sections of kinematic variables sensitive to models of new physics were derived. Anomalous quartic electroweak gauge couplings are introduced as dimensionless coupling parameters of additional operators within an effective field theory approach. Constraints on the parameters of operators with dimension eight were set employing a unitarization prescription based on form factors. info:eu-repo/classification/ddc/530 ddc:530

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