Left-right mixing on leptonic and semileptonic $b\to u$ decays

TL;DR

This paper investigates left-right mixing effects in $b o u$ decays to resolve discrepancies in $|V_{ub}|$ measurements, showing that new interactions can reconcile inclusive and exclusive decay results and alter certain branching fractions.

Contribution

It introduces the analysis of LR mixing effects in leptonic and semileptonic $b o u$ decays as a solution to the $|V_{ub}|$ discrepancy, providing quantitative estimates of their impact.

Findings

LR mixing can explain the $|V_{ub}|$ mismatch with Re$(\xi_u) \\approx -0.14$

Enhancement of $B o \tau\nu$ and $B \to \rho\ell\nu$ branching fractions by 30% and 17%

Reduction of $B \to \gamma\ell\nu$ branching fraction by 18%

Abstract

It has been known that there exists a disagreement emerged between the determination of $|V_{ub}|$ from inclusive $B \to X_u\ell\nu$ decays and exclusive $B \to \pi\ell\nu$ decays. In order to solve the mismatch, we investigate the left-right (LR) mixing effects, denoted by $\xi_u$, in leptonic and semileptonic $b \to u$ decays. We find that the new interactions $(V+A)\times (V-A)$ induced via the LR mixing can explain the mismatch between the values of $|V_{ub}|$ if Re$(\xi_{u})=-(0.14 \pm 0.12)$. Furthermore, we also find that the LR mixing effects can enhance the branching fractions for $B \to \tau\nu$ and $B \to \rho\ell\nu$ decays by 30% and 17%, respectively, while reducing the branching fraction for $B \to \gamma\ell\nu$ decays by 18%.