The B -> X_s gamma Photon Spectrum

TL;DR

This paper calculates the photon energy spectrum in B -> X_s gamma decay to high precision, enabling extraction of HQET parameters and insights into nonperturbative effects on Upsilon(1S) mass.

Contribution

It provides a next-to-next-to-leading order calculation of the photon spectrum, facilitating more accurate determination of HQET parameters from experimental data.

Findings

Computed the spectrum to order alpha_s^2 beta_0.

Extracted values for HQET parameters $ar extLambda$ and $ extlambda_1$.

Linked measurements to nonperturbative contributions in Upsilon(1S) mass.

Abstract

The photon energy spectrum in inclusive weak radiative B -> X_s gamma decay is computed to order alpha_s^2 beta_0. This result is used to extract a value for the HQET parameter $\bar\Lambda$ from the average <1-2E_\gamma/m_B>, and a value of the parameter $\lambda_1$ from <(1-2E_\gamma/m_B)^2>. An accurate measurement of <1-2E_\gamma/m_B> can determine the size of the nonperturbative contributions to the Upsilon(1S) mass which cannot be absorbed into the b quark pole mass.