Measurement of the ratio of partial branching fractions of inclusive B ¯ →xuℓ ν ¯ to B ¯ →xcℓ ν ¯ and the ratio of their spectra with hadronic tagging

Abstract

We present a measurement of the ratio of partial branching fractions of the semileptonic inclusive decays, B¯→Xuℓν¯ to B¯→Xcℓν¯, where ℓ=(e,μ), using the full Belle sample of 772×106 BB¯ pairs collected at the ϒ(4S) resonance. The identification of inclusive B¯→Xuℓν¯ decays is difficult due to the abundance of Cabibbo-Kobayashi-Maskawa-favored B¯→Xcℓν¯ events, which share a similar event topology. To minimize dependence on the modeling of these channels, a data-driven description of B¯→Xcℓν¯ is employed. The ratio is measured via a two-dimensional fit to the squared four-momentum transfer to the lepton pair, and the charged lepton energy in the B meson rest frame, where the latter must be la..