New ways to search for right-handed current in B -> rho ell nu decay

TL;DR

This paper proposes new angular asymmetry methods to detect potential right-handed current contributions in B -> rho ell nu decay, aiming to resolve discrepancies in |V_{ub}| measurements.

Contribution

It introduces generalized asymmetries as novel discriminators for right-handed currents, including a detailed analysis of theoretical uncertainties and measurement strategies.

Findings

Asymmetries can distinguish right-handed contributions without unbinned analysis.

Binned measurements can access full angular information, useful for background suppression.

Sensitivity estimates for BaBar, Belle, and Belle II data sets are provided.

Abstract

An interesting possibility to ease the tension between various determinations of |V_{ub}| is to allow a small right-handed contribution to the standard model weak current. The present bounds on such a contribution are fairly weak. We propose new ways to search for such a beyond standard model contribution in semileptonic B -> rho ell nu decay. Generalized asymmetries in one, two, or three angular variables are introduced as discriminators, which do not require an unbinned analysis of the fully differential distribution, and a detailed study of the corresponding theoretical uncertainties is performed. A discussion on how binned measurements can access all the angular information follows, which may be useful in both B -> rho ell nu and B -> K^* ell^+ ell^-, and possibly essential in the former decay due to backgrounds. The achievable sensitivity from the available BaBar and Belle data sets is explored, as well as from the anticipated 50 ab^{-1} Belle II data.