Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) and the direct CP asymmetry in B0 -> K*0 gamma

TL;DR

This paper reports precise measurements of the ratio of branching fractions for specific radiative B meson decays and the direct CP asymmetry in B0 -> K*0 gamma, providing important tests of the Standard Model.

Contribution

First measurement of the branching fraction ratio BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) with high precision and the most accurate CP asymmetry measurement in B0 -> K*0 gamma to date.

Findings

Branching fraction ratio is 1.23 +/- 0.06 (stat) +/- 0.04 (syst) +/- 0.10 (fs/fd)

Branching fraction BR(Bs0 -> phi gamma) is (3.5 +/- 0.4) x 10^{-5}

CP asymmetry is 0.8 +/- 1.7 (stat) +/- 0.9 (syst) %

Abstract

The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x 10^{-5}. The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/- 0.9(syst.))%. Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations.