Study of the $B^{0} \to \gamma \gamma$ decay at Belle and Belle II

Sumitted to PubDB: 2025-01-10

Category: Phd Thesis

Tags:

Principal Authors	Shubhangi Maurya
Date	2024-12-13
Belle II Number	BELLE2-PTHESIS-2025-001
Abstract	We report the result of a search for the rare decay $B^{0} \to \gamma \gamma$ using a combined dataset of $753\times10^{6}$ $B\bar{B}$ pairs collected by the Belle experiment and $387\times10^{6}$ $B\bar{B}$ pairs collected by the \mbox{Belle II} experiment at the $\rm \Upsilon(4S)$ resonance produced in electron-positron collisions. A simultaneous fit to the Belle and \mbox{Belle II} data sets yields $11.0^{+6.5}_{-5.5}$ signal events. We determine the branching fraction $\mathcal{B}(B^{0} \to \gamma\gamma) = (3.7^{+2.2}_{-1.8}(\rm stat)\pm0.5(\rm syst))\times10^{-8}$ with a signal significance of 2.5$\sigma$ and set a 90\% confidence level upper limit of $\mathcal{B}(B^{0} \to \gamma\gamma) < 6.4\times10^{-8}$. This result improves on the previously published 90\% confidence level upper limit by BABAR by a factor of about five and provides the most stringent limit to date.