Measurement of branching fractions, CP asymmetry, and isospin asymmetry for $\boldsymbol{B\rightarrow\rho\gamma}$ decays using Belle and Belle II data

TL;DR

This paper reports precise measurements of branching fractions, CP asymmetry, and isospin asymmetry in B to rho gamma decays using combined Belle and Belle II data, providing insights into flavor physics and potential new physics effects.

Contribution

First combined analysis of Belle and Belle II data for B to rho gamma decays, measuring branching fractions and asymmetries with improved precision.

Findings

Branching fraction for B+→ρ+γ: (13.1^{+2.0+1.3}_{-1.9-1.2})×10^{-7}

Branching fraction for B0→ρ0γ: (7.5±1.3^{+1.0}_{-0.8})×10^{-7}

Isospin asymmetry: (10.9^{+11.2+7.8}_{-11.7-7.3})%

Abstract

We present measurements of $B^{+}\rightarrow\rho^{+}\gamma$ and $B^{0}\rightarrow\rho^{0}\gamma$ decays using a combined data sample of $772 \times 10^6$ $B\overline{B}$ pairs collected by the Belle experiment and $387\times 10^6$ $B\overline{B}$ pairs collected by the Belle II experiment in $e^{+}e^{-}$ collisions at the $\Upsilon (4S)$ resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II data sets yields $114\pm 12$ $B^{+}\rightarrow\rho^{+}\gamma$ and $99\pm 12$ $B^{0}\rightarrow\rho^{0}\gamma$ decays. The measured branching fractions are $(13.1^{+2.0 +1.3}_{-1.9 -1.2})\times 10^{-7}$ and $(7.5\pm 1.3^{+1.0}_{-0.8})\times 10^{-7}$ for $B^{+}\rightarrow\rho^{+}\gamma$ and $B^{0}\rightarrow\rho^{0}\gamma$ decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry $A_{\rm I}(B\rightarrow\rho\gamma)=(10.9^{+11.2 +7.8}_{-11.7 -7.3})\%$ and the direct CP asymmetry $A_{CP}(B^{+}\rightarrow\rho^{+}\gamma)=(-8.2\pm 15.2^{+1.6}_{-1.2})\%$.