# CP Violation in ${\bar B}^0\to D^{*+}\mu^-{\bar\nu}_\mu$

## TL;DR

This paper proposes using CP-violating angular asymmetries in ${ar B}^0 o D^{*+} o D^0 \pi^+$ and $ au$ decay processes to distinguish new physics models explaining anomalies in semileptonic B decays.

## Contribution

It introduces a method to differentiate NP models via CP violation measurements in specific B decay channels, despite experimental challenges.

## Key findings

- CP-violating asymmetries can distinguish NP models
- Nonzero CP violation would rule out popular models
- Measurements can differentiate among various leptoquark models

## Abstract

In order to explain the observed anomalies in the measurements of $R_{D^{(*)}}$ and $R_{J/\psi}$, a variety of new-physics (NP) models that contribute to $b\to c\tau^-{\bar\nu}$ have been proposed. In this paper, we show how CP-violating observables can be used to distinguish these NP models. Because ${\vec p}_\tau$ cannot be measured (the decay products of the $\tau$ include the undetected $\nu_\tau$), obtaining the angular distribution of ${\bar B}^0\to D^{*+}\tau^{-}{\bar\nu}_\tau$ is problematic. Instead, we focus here on ${\bar B}^0\to D^{*+}(\to D^0 \pi^+)\mu^- {\bar\nu}_\mu$. This process may also receive contributions from the same NP, and LHCb intends to measure the CP-violating angular asymmetries in this decay. There are two classes of NP models that contribute to $b\to c\mu^-{\bar\nu}_\mu$. These involve (i) a $W'$ (two types) or (ii) a leptoquark (LQ) (six types). The most popular NP models predict no CP-violating effects, so the measurement of nonzero CP-violating symmetries would rule them out. Furthermore these measurements allow one to distinguish the $W'$ and LQ models, and to differentiate among several LQ models.