Closing the knowledge gap in semileptonic $B\rightarrow X_c\ell\nu$ decays

TL;DR

This paper reviews current measurements of semileptonic B decays to charm mesons, identifies unmeasured components likely involving baryons and D_s mesons, and suggests future search directions.

Contribution

It evaluates the gap between exclusive and inclusive semileptonic B decay measurements and proposes candidate final states to complete the decay rate.

Findings

Unmeasured components are dominated by final states without D mesons.

Final states involving baryons and D_s mesons are significant contributors.

Proposed models for specific decay channels contribute marginally to the total rate.

Abstract

In this work we summarize the current status of measured exclusive semileptonic branching fractions containing charm mesons. We use the available experimental data to evaluate the difference between the sum of exclusive measurements and the inclusive determination. By including experimental results of branching fractions relative to semi-inclusive $B\rightarrow D X\ell\nu$ decays, we demonstrate that the unmeasured components of the total branching fraction are dominated by final states devoid of $D$ mesons, hinting towards sizeable contributions from baryonic final states and $D_s$ mesons. Based on the obtained fractions, we discuss candidates that could potentially close the remaining difference and propose searches for promising final states. Furthermore, we provide simplified models for S-wave $B\rightarrow D\eta\ell\nu$ and $B\rightarrow D_s K\ell\nu$ decays that contribute marginally to the unmeasured components of the total inclusive rate.