Search for lepton universality violation through b → sℓ+ℓ− mediated rare decays at Belle II

Sumitted to PubDB: 2025-04-28

Category: Phd Thesis

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Principal Authors	Soumen Halder, Gagan Mohanty
Date	2024-04-16
Belle II Number	BELLE2-PTHESIS-2025-006
Abstract	We report on the progress made at Belle II in probing lepton universality violation through rare B meson decays mediated by b → sℓ+ℓ− transitions. Key measurements include branching fractions for B+ → K+ℓ+ℓ− decays, with ℓ representing an electron or a muon. Lepton universality, quantified by the observable RK, is investigated across a broad range of the dilepton invariant-mass squared excluding charmonium resonance regions. Validation of lepton universality studies is performed through the measurement of absolute branching fractions for B → KJ/ψ(ℓ+ℓ−) decays, the lepton universality observable RK(J/ψ), and isospin asymmetries. The rediscovery of other decays involving b → sℓ+ℓ− transitions is also discussed, particularly the branching fraction for B → K∗ℓ+ℓ− decays. Lastly, we discuss the performance of the silicon-strip vertex detector of Belle II during its commissioning phase.