New Physics effect on $B_c\to J/\psi \tau \bar{\nu }$ in relation to the $R_{D^{(\ast )}}$ anomaly

Abstract

We study possible new physics (NP) effects on $B_c\to J/\psi \tau \bar{\nu }$, which has been recently measured at LHCb as the ratio of $R_{J/\psi }=\mathcal{B}(B_c\to J/\psi \tau \bar{\nu })/\mathcal{B}(B_c\to J/\psi \mu \bar{\nu })$. Combining it with the long-standing $R_{D^{(\ast )}}$ measurements, in which the discrepancy with the prediction of the standard model is present, we find possible solutions to the anomaly by several NP types. Then, we see that adding the $R_{J/\psi }$ measurement does not improve NP fit to data, but the NP scenarios still give better ${\chi }^2$ than the SM. We also investigate indirect NP constraints from the lifetime of $B_c$ and NP predictions on the $\tau$ longitudinal polarization in $\bar{B}\to D^{\ast }\tau \bar{\nu }$.

Comments: 7 pages, 2 figures, 1 table, (v2) new constraint included, (v2) references added, (v3) published version with additional revision