Bc- → J/ψ (→μ+μ-)τ-(→π-ντ, ρ-ντ, l-(ν)over-barlντ)(ν)over-barτ decays with visible final-state kinematics

The semitauonic B-c(-) -> J/psi tau(-)(nu) over bar (tau) decay provides an ideal and clean mode to scrutinize possible new physics effects in b -> c(tau)-(nu) over bar (tau) transitions as indicated by the current data on R(D(*)) anomalies. In this work, we use the spin density matrix method to obtain the maximum information on the underlying physics of B-c(-) J/psi tau(-)(nu) over bar (tau) decay with both polarized tau lepton and J/psi meson. Their subsequent decays, with J/psi -> mu(+)mu(-) as well as tau(-)-> pi(-)nu(tau), tau(-) -> rho(-)tau and tau(-) -> l(-)(nu) over bar (l)nu(tau), are exploited to extract the energy and angular distributions of the charged final-state particles in the processes. Starting with the most general effective Hamiltonian relevant for the b -> c tau(-)nu(tau) transitions, including all possible Lorentz structures of the dimension-six operators with both left-and right-handed neutrinos, we first derive the five-fold differential decay rate in terms of the visible final-state kinematics. From this distribution, we then construct in total 34 normalized observables, among which nine refer to the CP-violating triple product asymmetries that vanish within the Standard Model. We also construct five new observables based on the combinations of these normalized observables that can only be attributed to the right-handed neutrinos. On the other hand, considering the low statistics of the fully differential distribution, we introduce some integrated observables with only one kinematic variable left, which are more promising to be measured due to the largely increased statistics. The sensitivities of all these observables to the different new physics scenarios are investigated in detail. Finally, assuming an ideal circumstance, we give an estimate of the statistical uncertainties of the nine CP-conserving observables at LHCb and found that tau(-) -> pi(-)nu(tau) has the highest analyzing power among the three tau decay channels.

Automated summary

The semitauonic B-c -> J/psi tau decay is a clean mode to investigate new physics effects in b -> c(tau)-(nu) over bar (tau) transitions. The spin density matrix method is used to study the underlying physics of the B-c- J/psi tau decay, considering both polarized tau lepton and J/psi meson. The energy and angular distributions of the charged final-state particles are extracted by studying the subsequent decays of J/psi -> mu+mu- and tau- -> pi- nu(tau), tau- -> rho- tau, and tau- -> l-(nu) over bar (l) nu(tau).