Titel: Measurement of the photon energy spectrum in inclusive radiative B meson decays using the hadronic-tagging method
Sprache: Englisch
Autor*in: Svidras, Henrikas
Schlagwörter: electroweak decays; B-physics; hadronic tagging; radiative decays; rare decays; precision measurements
GND-Schlagwörter: B-MesonGND
Flavour <Elementarteilchen>GND
Maschinelles LernenGND
Standardmodell <Elementarteilchenphysik>GND
Erscheinungsdatum: 2023
Tag der mündlichen Prüfung: 2023-03-13
This doctoral thesis presents an inclusive analysis of the photon energy spectrum in radiative B meson decays (B → Xs γ) that involve strange hadrons and a photon. The data set consists of Υ(4S) mesons that primarily decay into pairs of B mesons. The partner B meson is fully reconstructed in a large number of hadronic decay channels using multivariate classifiers. This full reconstruction allows for the inference of the momentum and energy of the signal B meson through a technique referred to as hadronic-tagging. The data set analysed corresponds to an integrated luminosity of 189 fb⁻¹ of electron-positron collisions at the Υ(4S) resonance energy provided by the SuperKEKB accelerator. This is the first measurement of the B → Xs γ decay with the Belle II experiment. Only the high energy photon from the signal B meson decay is reconstructed in order to achieve an unbiased inclusive sample of final states involving strange hadrons. The hadronic-tagging provides direct access to the signal B meson rest frame, leading to the photon energy spectrum without the additional kinematic smearing observed in the Υ(4S) rest frame. The partial branching fractions of the B → Xs γ decay are measured in eight intervals of photon energy in the signal B meson rest frame between 1.8-2.7 GeV The obtained signal yield for this photon energy range is 343 ± 122 events. The integrated branching fraction in this region is found to be (3.54 ± 0.78 (stat.) ± 0.83 (syst.)) ⋅ 10⁻⁴. Additionally, the first and second moments of the photon energy spectrum are calculated for several photon energy thresholds. For photon energies above 1.8 GeV, they are determined to be (2.284 ± 0.065 (stat.) ± 0.071 (syst.)) GeV and (0.0502 ± 0.0157 (stat.) ± 0.0176~(syst.)) GeV², respectively. The results show excellent agreement with the Standard Model predictions and serve as a proof-of-concept for future hadronic-tagged radiative measurements at Belle II.
URL: https://ediss.sub.uni-hamburg.de/handle/ediss/10177
URN: urn:nbn:de:gbv:18-ediss-108136
Dokumenttyp: Dissertation
Betreuer*in: Tackmann, Kerstin
Schleper, Peter
Enthalten in den Sammlungen:Elektronische Dissertationen und Habilitationen

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