000003493 001__ 3493
000003493 005__ 20230330122051.0
000003493 037__ $$aBELLE2-PTHESIS-2023-005
000003493 041__ $$aeng
000003493 100__ $$aHenrikas Svidras
000003493 245__ $$aMeasurement of the photon energy spectrum in inclusive radiative B meson decays using the hadronic-tagging method
000003493 260__ $$aHamburg$$bDESY$$c2023
000003493 300__ $$a257
000003493 500__ $$aPresented on 13 03 2023
000003493 502__ $$aPhD$$bHamburg, University of Hamburg$$c2023
000003493 520__ $$aThis doctoral thesis presents an inclusive analysis of the photon energy spectrum in radiative B meson decays (B → Xs γ) that involve strange hadrons and a photon. The data set consists of Υ(4S) mesons that primarily decay into pairs of B mesons. The partner B meson is fully reconstructed in a large number of hadronic decay channels using multivariate classifiers.  This full reconstruction allows for the inference of the momentum and energy of the signal B meson through a technique referred to as hadronic-tagging. The data set analysed corresponds to an integrated luminosity of 189 fb⁻¹ of electron-positron collisions at the Υ(4S) resonance energy provided by the SuperKEKB accelerator.  This is the first measurement of the B → Xs γ decay with the Belle II experiment. Only the high energy photon from the signal B meson decay is reconstructed in order to achieve an unbiased inclusive sample of final states involving strange hadrons.  The hadronic-tagging provides direct access to the signal B meson rest frame, leading to the photon energy spectrum without the additional kinematic smearing observed in the Υ(4S) rest frame. The partial branching fractions of the B → Xs γ decay are measured in eight intervals of photon energy in the signal B meson rest frame between 1.8-2.7 GeV  The obtained signal yield for this photon energy range is 343 ± 122 events.  The integrated branching fraction in this region is found to be (3.54 ± 0.78 (stat.) ± 0.83 (syst.)) ⋅ 10⁻⁴. Additionally, the first and second moments of the photon energy spectrum are calculated for several photon energy thresholds.  For photon energies above 1.8 GeV, they are determined to be (2.284 ± 0.065 (stat.) ± 0.071 (syst.)) GeV and (0.0502 ± 0.0157 (stat.) ± 0.0176~(syst.)) GeV², respectively. The results show excellent agreement with the Standard Model predictions and serve as a proof-of-concept for future hadronic-tagged radiative measurements at Belle~II.
000003493 700__ $$aKerstin Tackmann$$edir.
000003493 8560_ $$fhenrikas.svidras@desy.de
000003493 8564_ $$uhttps://docs.belle2.org/record/3493/files/BELLE2-PTHESIS-2023-005.pdf
000003493 980__ $$aTHESIS