Branching Fraction and Photon Energy Spectrum b -> s gamma

TL;DR

The branching fraction and photon energy spectrum for the radiative penguin process b-->s gamma is measured, and the heavy quark effective theory parameter Lambda is obtained from the modified minimal subtraction renormalization scheme.

Abstract

We have measured the branching fraction and photon energy spectrum for the radiative penguin process b -> s gamma. We find BR(b -> s gamma) = (3.21 +- 0.43 +- 0.27 +0.18 -0.10) 10^(-4), where the errors are statistical, systematic, and from theory corrections. We obtain first and second moments of the photon energy spectrum above 2.0 GeV, < E_γ> = 2.346 +- 0.032 +- 0.011 GeV, and <E^2_gamma> - <E_gamma>^2 = 0.0226 +- 0.0066 +- 0.0020 GeV^2, where the errors are statistical and systematic. From the first moment we obtain (in MS[Bar], to order 1/M^3 and beta_0 alpha_s^2) the HQET parameter Lambda[Bar] = 0.35 +- 0.08 +- 0.10 GeV.

Figures (2)

• Figure 1: Photon energy spectra (weights per 100 MeV). The upper plot (a) shows the On $\Upsilon(4S)$ and scaled Off-resonance spectra. The lower plot (b) shows their difference, and the spectrum estimated for $B$ decay processes other than $b \rightarrow s \gamma$ and $b \rightarrow d \gamma$.
• Figure 2: Observed laboratory frame photon energy spectrum (weights per 100 MeV) for On minus scaled Off minus $B$ backgrounds, the putative $b \rightarrow s \gamma$ plus $b \rightarrow d \gamma$ signal. No corrections have been applied for resolution or efficiency. Also shown is the spectrum from Monte Carlo simulation of the Ali-Greub spectator model with parameters $\langle m_b \rangle$ = 4.690 GeV, $P_F$ = 410 MeV/c, a good fit to the data.