Measurement of the inclusive $B\to X_{s+d} \gamma$ branching fraction, photon energy spectrum and HQE parameters

TL;DR

This paper measures the inclusive $B o X_{s+d} \gamma$ branching fraction and photon energy spectrum using Belle data, providing new results on Heavy Quark Expansion parameters and photon energy thresholds.

Contribution

It presents the first measurement of the inclusive $B o X_{s+d} \gamma$ branching fraction with detailed spectrum analysis and extraction of HQE parameters from Belle data.

Findings

Branching fraction for $B o X_s \gamma$ at 1.8 GeV threshold: (3.01 ± 0.10 (stat) ± 0.18 (syst) ± 0.08 (model))×10^{-4}

Heavy quark parameters: $m_b = 4.626 ± 0.028$ GeV, $\mu_\pi^2 = 0.301 ± 0.063$ GeV$^2$

Photon energy spectrum results constrain HQE parameters and test Standard Model predictions.

Abstract

We report a measurement of the inclusive $B\to X_{s+d} \gamma$ and $B\to X_{s} \gamma$ branching fractions using a data set of $(772 \pm 11)\times 10^6$ $B\bar{B}$ pairs collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Results are presented for photon energy thresholds between 1.7 to 2.0 GeV. For the 1.8 GeV threshold we find $\mathcal{B}_{s\gamma} = (3.01 \pm 0.10~\text{(stat)} \pm 0.18~\text{(syst)} \pm 0.08~\text{(model)})\times 10^{-4}$. The Heavy Quark Expansion parameters that best fit the spectrum in the shape-function scheme are $m_{b} = (4.626 \pm 0.028) \text{GeV}$ and $ \mu_{\pi}^{2} = (0.301\pm 0.063) \text{GeV}^2$.