CP Violation in ${bar B}^0to D^{*+}mu^-{bar u}_mu$

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 $bto ctau^-{bar u}$ 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 $ u_tau$), obtaining the angular distribution of ${bar B}^0to D^{*+}tau^{-}{bar u}_tau$ is problematic. Instead, we focus here on ${bar B}^0to D^{*+}(to D^0 pi^+)mu^- {bar u}_mu$. 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 $bto cmu^-{bar u}_mu$. 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.