Measurement of the ratio of branching fractions $\frac{\mathcal{BR}(B^0\to K^*\gamma)}{\mathcal{BR}(B_s^0\to\phi\gamma)}$

TL;DR

This paper reports a preliminary measurement of the ratio of branching fractions between two rare B-meson radiative decays, providing insights into the Standard Model and photon polarization at LHCb.

Contribution

First measurement of the ratio of branching fractions for $B^0 o K^* ext{ }\gamma$ and $B_s^0 o ext{ }\phi ext{ }\gamma$ decays using early LHCb data.

Findings

Measured ratio of branching fractions: 1.52±0.14(stat.)±0.10(syst.)±0.12(f_s/f_d)

Inferred $B_s^0 o ext{ }\phi ext{ }\gamma$ branching fraction as (2.8±0.5)×10^{-5}

Provides a baseline for photon polarization studies in B-meson decays.

Abstract

The interest to the rare radiative decays of the B-mesons at LHCb is mostly aroused due to the measurement of the photon polarization in the $B_s^0\to\phi\gamma$ decay, which may provide a sensitive probe for the Standard Model. The LHCb experiment has started to take data at the energy of $\sqrt{s} = 7 TeV$ in 2010 and the current paper presents the result of the studies of the two rare radiative decays $B^0\to K^*\gamma$ and $B_s^0\to\phi\gamma$ with $340 pb^{-1}$ of data taken in the first half of 2011. With this data we have a preliminary measurement of $\frac{\mathcal{BR}(B^0\to K^*\gamma)}{\mathcal{BR}(B_s^0\to\phi\gamma)} = 1.52\pm0.14(stat.)\pm0.10(syst.)\pm0.12(f_s/f_d)$ and assuming the measured value of $\mathcal{B}(B^0\to K^*\gamma) = (4.33 \pm 0.15)\times10^{-5}$ we infer $\mathcal{B}(B_s^0\to \phi\gamma) = (2.8\pm0.5)\times10^{-5}$ \cite{bib:conf}.