Measurement of lepton mass squared moments in B→Xcℓν¯ℓ decays with the Belle II experiment

Abstract

We present measurements of the first to fourth moments of the lepton mass squared q2 of 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 62.8 fb−1 of integrated luminosity and collected by the Belle II 2 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>1.5 GeV2/c4 up to q2>8.5 GeV2/c4, probing up to 77% of the accessible B→Xcℓν¯ℓ phase space. This is the first measurement of moments in the experimentally challenging range of [1.5,2.5] GeV2/c4. The results can be used for a new determination of |Vcb| using inclusive B→Xcℓν¯ℓ decays.9 MoreReceived 16 May 2022Accepted 20 October 2022DOI:https://doi.org/10.1103/PhysRevD.107.072002Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHeavy quark effective theoryLeptonic, semileptonic & radiative decaysPhysical SystemsBottom mesonsTechniquesParticle data analysisPrecision measurementsParticles & Fields