Seema Choudhury

30 December 2023

Abstract: We present the recent results of the rare decays from the Belle and Belle II experiments, collected at the Y(4S) resonance. The data sample from Belle is 711/fb, and 189/fb or 361/fb data sample from Belle II. Here, we report five rare decays involving b→s (d) transitions. The measurement of branching fractions for B→K*ll decays using 189/fb data sample from Belle II is consistent with the world averages. The best upper limits for lepton-flavor-violating B→K*τl decays using the Belle data sample are <(0.59 - 2.45)x 10^-5 at a 90% confidence level. The first ever search for B→K*ττ decay at Belle and the 90% confidence level upper limit is <3.1 x 10^{-3}. Belle II has measured the photon-energy spectrum in radiative B decays into inclusive final states involving a hadron and a photon using 189/fb data sample. The branching fraction measurements for different photon energy bins are consistent with the world averages. The measurement of branching fraction, isospin asymmetry, and CP-asymmetry for the exclusive B→ργ decay using combined data samples from Belle and Belle II are the most precise to date.

Keyword(s): Rare decays ; Belle ; Belle II