Moments of the photon energy spectrum from $B\to X_s γ$ decays measured by Belle

TL;DR

This work reports preliminary measurements of the first and second moments of the inclusive $B\rightarrow X_s\gamma$ photon energy spectrum across lower photon-energy thresholds $E^*_{cut}$ between 1.8 and 2.3 GeV, using Belle data from $\Upsilon(4S)$. Moments are extracted after unfolding and correcting for detector effects and the $B$-boost, including a bias correction from a signal MC; these results constrain HQET parameters $m_b$ and $\mu_\pi^2$ (or $\bar{\Lambda}$ and $\lambda_1$) and provide cross-checks with KN prescriptions. A KN-based cross-check shows good agreement, and the measurements align with prior results from CLEO and BaBar. The analysis delivers precise inputs for determining CKM elements and heavy-quark parameters with controlled systematics.

Abstract

We report preliminary measurements of the first (mean) and second moment (variance) of the inclusive photon energy spectrum in $B\to X_sγ$ decays, for threshold values of the photon energy in the range 1.8--2.3 GeV as measured in the rest frame of the $B$-meson. These results are obtained from the Belle measurement of the spectrum, which used a data set consisting of 152 million $B\bar{B}$ pairs collected by the Belle detector at the KEKB asymmetric-energy electron-positron collider operated on the $Υ(4S)$ resonance.

Figures (3)

• Figure 1: From Koppenburg:2004fz. (a) Photon energy spectra in the $\Upsilon(4S)$ frame. (b) Efficiency-corrected photon energy spectrum. The two error bars show the statistical and total errors.
• Figure 2: $B\rightarrow X_s \gamma$ photon spectrum (a) mean and (b) variance as a function of $E_{\mathrm{cut}}$.
• Figure 3: Comparison of $B\rightarrow X_s \gamma$ photon spectra (a) mean and (b) variance as a function of $E_{\mathrm{cut}}$ between our measured moments and those predicted in the Kagan-Neubert prescription using corresponding values of the parameters that best fit the spectrum.