Scrutinizing New Physics in Semi-leptonic $B_c\to J/\psi \tau \nu$ Decay

Abstract

We perform a global analysis of the $b\to c\tau \nu$ data using the recent lattice results on the $B_c\to J/\psi$ vector and axial-vector form factors. To explore the effects from the tensor operator of new physics beyond the standard model, we determine the tensor form factors by using the non-relativistic QCD (NRQCD) relations between tensor and (axial-)vector form factors. Based on the lattice+NRQCD form factors, we fit the Wilson coefficients and the new physics couplings in $R_2$, $S_1$ and $U_1$ leptoquark models by including the recently measured $R({\Lambda }_c)$ and imposing the relaxed constraint $\mathcal{B}(B_c\to J/\psi )<30\%$ in light of the recent studies on LEP1 data and $B_c$ lifetime. We give predictions for the experimental observables including $R(J/\psi )$, $P_{\tau }(J/\psi )$, $F_L(J/\psi )$ and ${\mathcal{A}}_{FB}(J/\psi )$ as well as their $q^2$ distribution in new physics scenarios/models. Our results suggest that the longitudinal $\tau$ polarization fraction $P_{\tau }(J/\psi )$ and the forward-backward asymmetry ${\mathcal{A}}_{FB}(J/\psi )$ are useful for testing the $R_2$ leptoquark model.

19 pages, 10 figures and 6 tables

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Cited by in corpus (9)

• Next-to-next-to-leading order matching of beauty-charmed meson $B_c$ and $B_c^{\ast }$ decay constants
• Systematic analysis of the form factors of $B_c\to {\eta }_c$, $J/\psi$ and corresponding weak decays
• Baryonic heavy-to-light form factors induced by tensor current in light-front approach
• $B_c^{-}\to J/\psi (\to {\mu }^{+}{\mu }^{-}){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau },{\rho }^{-}{\nu }_{\tau },{\ell }^{-}{\bar{\nu }}_{\ell }{\nu }_{\tau }){\bar{\nu }}_{\tau }$ decays with visible final-state kinematics
• Systematic analysis of the form factors of $B_c$ to $P$-wave charmonia and corresponding weak decays
• Nonleptonic $B_c$ decay rates from model independent relations
• Flavour Anomalies: A comparative analysis using a machine learning algorithm
• ${\eta }_c$ leading-twist distribution amplitude and the $B_c\to {\eta }_c\ell {\bar{\nu }}_{\ell }$ semileptonic decays using QCD Sum Rules
• The Angular Observables of ${\Lambda }_b\to {\Lambda }_c(\to {\Lambda }^0{\pi }^{+}){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau }){\bar{\nu }}_{\tau }$ within the Paradigm of FCCC Anomalies