Thesis BELLE2-PTHESIS-2021-007

Measurement of Branching Fractions of B -> Xs l+ l− Decays at the Belle II experiment

Yo Sato

Tohoku University Sendai, Miyagi

Abstract: The inclusive B -> Xs l+ l- decays are a great probe to search for physics beyond the standard model (SM) of particle physics. The process is a flavor-changing-neutral-current (FCNC) process which proceeds via loop diagrams in the standard model and thus are strongly suppressed. Since a new heavy particle might be able to enter the loop, the FCNC is sensitive for new physics. Moreover, B -> Xs l+l- decays provide complementary information with less hadronic uncertainty to the exclusive B -> K(*) l+ l- decays in which tensions from the SM prediction have been observed. Belle II is a unique experiment to explore the process with large statistics to shed light on the anomalies. We performed the measurements of the branching fractions of B -> Xs l+ l- decay using the data set accumulated by Belle II experiment which corresponds to 37.7 million B-meson pairs. This is the first measurement on B -> Xs l+ l- at Belle II experiment. Because the statistical significance on muon modes and combined mode is less than 2-sigma level, the upper limit on the branching fraction is set for these modes. The branching fraction of B -> Xs e+ e- and B -> Xs mu+ mu- is consistent with previous measurements and the SM prediction. Result of B -> Xs l+ l- is consistent with the world average, Belle measurement and the SM prediction, while the difference from BaBar is at 1.4-sigma level. The analysis procedure of B -> Xs l+ l- decays at Belle II experiment well established and we have got ready to lead decisive conclusions regarding the anomalies which are observed in the exclusive B -> K(*) l+ l- decays with upcoming Belle II data.

Note: Presented on 28 01 2021
Note: PhD

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 Record created 2021-06-28, last modified 2021-06-28

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