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Belle II
Abstract:
We present measurements of the first to fourth moments of the lepton mass squared q2 of \mbox{B→Xcℓν¯ℓ} decays for ℓ=e,μ and with Xc a hadronic system containing a charm quark. These results use a sample of electron-positron collisions at the Υ(4S) resonance corresponding to 62.8fb−1 of integrated luminosity and collected by the Belle II experiment in 2019 and 2020. To identify the Xc system and reconstruct q2, one of the B mesons from an Υ(4S)→BB¯¯¯ decay is fully reconstructed in a hadronic decay mode using a multivariate B tagging algorithm. We report raw and central moments for q2>1.5GeV2/c4 up to q2>8.5GeV2/c4, probing up to 77\% of the accessible \mbox{B→Xcℓν¯ℓ} phase space. This is the first measurement of moments in the experimentally challenging range of [1.5,2.5]GeV2/c4.
