Measurement of Hadronic Mass Moments $\langle M_X^n \rangle $ in $B \rightarrow X_c \ell \nu $ Decays at Belle II

TL;DR

This paper reports the first six hadronic mass moments in semileptonic B decays at Belle II, providing data crucial for determining CKM matrix elements and quark masses using Heavy Quark Expansions of QCD.

Contribution

It presents novel measurements of hadronic mass moments in B decays using Belle II data, advancing the precision of CKM and quark mass determinations.

Findings

Measured hadronic mass moments $raket{M_X^n}$ for n=1 to 6.

Used Belle II data with 34.6 fb$^{-1}$ for the analysis.

Results as a function of lepton momentum cut.

Abstract

We present measurements of the first six hadronic mass moments in semileptonic $B \rightarrow X_c \ell \nu $ decays. The hadronic mass moments, together with other observables of inclusive $B$ decays, can be used to determine the CKM matrix element $|{V_{cb}}|$ and mass of the $b$-quark $m_b$ in the context of Heavy Quark Expansions of QCD. The Belle~II data recorded at the $\Upsilon (4S)$ resonance in 2019 and 2020 (March-July), corresponding to an integrated luminosity of $34.6\;\mathrm{fb}^{-1}$, is used for this measurement. The decay $\Upsilon (4S) \rightarrow B \overline{B}$ is reconstructed by applying the hadronic tagging algorithm provided by the Full Event Interpretation to fully reconstruct one $B$ meson. The second $B$ meson is reconstructed inclusively by selecting a high-momentum lepton. The $X_c$ system is identified by the remaining reconstructed tracks and clusters in the electromagnetic calorimeter. We report preliminary results for the hadronic mass moments $\langle M_X^n \rangle $ with $n=1,\dots,6$, measured as a function of a lower cut on the lepton momentum in the signal $B$ rest frame.