Improved Measurement of Inclusive Radiative B-meson decays

TL;DR

This paper presents a precise measurement of the inclusive radiative decay rate of B-mesons into Xs gamma, covering most of the spectrum, with detailed moments of the photon energy distribution, advancing understanding of flavor-changing neutral currents.

Contribution

It provides the first and second moments of the photon energy spectrum for B to Xs gamma decays down to 1.7 GeV, improving the accuracy of decay rate measurements.

Findings

Branching fraction measured as (3.31 ± 0.19 ± 0.37 ± 0.01)×10^{-4}.

Spectrum moments extended down to 1.7 GeV.

Results are preliminary and improve existing decay measurements.

Abstract

We report a fully inclusive measurement of the flavor changing neutral current decay $B\to X_s\gamma$ in the energy range $1.7 \GeV\le E^\mathrm{c.m.s}_\gamma\le 2.8 \GeV$, covering 97% of the total spectrum, where c.m.s is the center of mass system. Using $605\ifb$ of data, we obtain in the rest frame of the $B$-meson ${\mathcal B}(B\to X_s\gamma : E^B_\gamma>1.7 \mathrm{GeV})= (3.31 \pm 0.19 \pm 0.37 \pm 0.01)\times 10^{-4}$, where the errors are statistical, systematic and from the boost correction needed to transform from the rest frame of the $\Upsilon(4S)$ (c.m.s) to that of the $B$-meson, respectively. We also measure the first and second moments of the photon energy spectrum as functions of various energy thresholds, which extend down to $1.7 \GeV$. The results are preliminary.