CP Violation in ${\bar B}^0\to D^{*+}μ^-{\barν}_μ$

In order to explain the observed anomalies in the measurements of $R_{D^{(*)}}$ and $R_{J/ψ}$, a variety of new-physics (NP) models that contribute to $b\to cτ^-{\barν}$ have been proposed. In this paper, we show how CP-violating observables can be used to distinguish these NP models. Because ${\vec p}_τ$ cannot be measured (the decay products of the $τ$ include the undetected $ν_τ$), obtaining the angular distribution of ${\bar B}^0\to D^{*+}τ^{-}{\barν}_τ$ is problematic. Instead, we focus here on ${\bar B}^0\to D^{*+}(\to D^0 π^+)μ^- {\barν}_μ$. 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 $b\to cμ^-{\barν}_μ$. 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.

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