Measurement of the Moments of the Photon Energy Spectrum in B -> X_s gamma Decays and Determination of |V_cb| and m_b at Belle

TL;DR

This paper measures moments of the photon energy spectrum in B meson decays and uses these to precisely determine the CKM matrix element |V_cb| and the b-quark mass through theoretical fits in different schemes.

Contribution

It provides the first and second moments of the photon energy spectrum in B decays and extracts |V_cb| and m_b using combined experimental data and theoretical models.

Findings

|V_cb| around 41.6 x 10^{-3} with ~1.7% uncertainty

b-quark mass approximately 4.54 GeV in kinetic scheme

Consistent results across 1S and kinetic schemes

Abstract

Using the previous Belle measurement of the inclusive photon energy in $B\to X_s\gamma$ decays, we determine the first and second moments of this spectrum for minimum photon energies in the $B$ meson rest frame ranging from 1.8 to 2.3 GeV. Combining these measurements with recent Belle data on the lepton energy and hadronic mass moments in $B\to X_c\ell\nu$ decays, we perform fits to theoretical expressions derived in the 1S and kinetic mass schemes and extract the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{cb}$, the $b$-quark mass and other non-perturbative parameters. In the 1S scheme analysis we find $|V_{cb}|=(41.56\pm 0.68(\mathrm{fit})\pm 0.08(\tau_B))\times 10^{-3}$ and $m_b^\mathrm{1S}=(4.723\pm 0.055)$ GeV. In the kinetic scheme, we obtain $|V_{cb}|=(41.58\pm 0.69(\mathrm{fit})\pm 0.08(\tau_B)\pm 0.58(\mathrm{th}))\times 10^{-3}$ and $m_b^\mathrm{kin}=(4.543\pm 0.075)$ GeV.