Study of radiative <em>B → X_s+dΥ</em> decays at Belle

Abstract

An analysis of the decay <i>B → X_s+d γ</i> using the complete <i>Υ(4S)</i> data sample of the Belle experiment is presented. This inclusive analysis, reconstructs only the high energy photon from the signal <i>B</i> meson and a lepton from the partner <i>B</i>, with the purposes of flavor tagging and background suppression. The branching fraction is measured for several photon energy (<i>E^*_γ</i>) thresholds and extrapolated to the 1.6 GeV point. For the <i>E^*_γ ></i> 1.8 GeV the measured value is <i>B_sγ</i> = (3.12 ± 0.10(stat) ± 0.19(syst) ± 0.08(model) ± 0.04(extrap) ) × 10^-4, consistent with Standard Model predictions. It allows to set a lower bound on the mass of a charged Higgs boson on the Two-Higgs-Doublet-Model of type II of <i>m_H⁺</i> > 580 GeV. The <i>CP</i> asymmetry (<i>A^CP_(s+d)γ</i>) is measured for several photon energy thresholds, testing its independence from this choice. The result is consistent with Standard Model expectations, for the <i>E^*_γ</i> > 2.1 GeV the asymmetry is <i>A^CP_(s+d)γ</i> = (2.2 ± 3.9(stat) ± 0.9(syst))%. An analysis of the photon energy spectrum allows to extract the HQE parameters <i>m_b</i> = (4.627 ^+0.030_-0.031) GeV and <i>μ_π²</i> = (0.301 ^+0.070_-0.066) GeV². The values for the first and second spectral moments are also measured for several photon energy thresholds, for <i>E^*_γ</i> > 1.8 GeV the measured values are <i><E^*_γ></i> = (2.320 ± 0.016 ± 0.047 ± 0.001) GeV and <i>< ΔE^*_γ></i> = (4.258 ± 0.525 ± 1.498 ± 0.050) × 10^-2 GeV².