Measurement of branching fractions, isospin and CP-violating asymmetries for exclusive \boldmath$b \to d\gamma$ modes

TL;DR

This paper presents new measurements of branching fractions, isospin asymmetry, and CP violation in specific rare B meson decays involving a photon, using a large data sample from the Belle experiment.

Contribution

It provides the first measurement of direct CP-violating asymmetry in $B^+ o ho^+ \gamma$ decays and updates branching fractions and isospin asymmetry with a large data set.

Findings

Branching fractions measured with uncertainties.

First measurement of direct CP asymmetry in these decays.

Isospin asymmetry found to be negative.

Abstract

We report new measurements of the decays $B\to\rho^+ \gamma$, $B \to \rho^0 \gamma$ and $B \to \omega\gamma$ using a data sample of $657 \times 10^6$ $B$ meson pairs accumulated with the Belle detector at the KEKB $e^+ e^-$ collider. We measure branching fractions ${\cal B}(B^+ \to \rho^+ \gamma) = (8.7^{+2.9}_{-2.7}{}^{+0.9}_{-1.1})\times 10^{-7}$, ${\cal B}(B^0 \to \rho^0 \gamma) = (7.8^{+1.7}_{-1.6}{}^{+0.9}_{-1.0}) \times 10^{-7}$ and ${\cal B}(B^0 \to \omega \gamma) = (4.0^{+1.9}_{-1.7} \pm 1.3) \times 10^{-7}$. We also report the isospin asymmetry $\Delta (\rho\gamma) = -0.48^{+0.21}_{-0.19}{}^{+0.08}_{-0.09}$; and the first measurement of the direct CP-violating asymmetry $A_{CP}(B^+ \to \rho^+ \gamma) = -0.11\pm{0.32}\pm{0.09}$, where the first and second errors are statistical and systematic, respectively.