Scrutinizing New Physics in Semi-leptonic $B_{c}\rightarrow J/ψτν$ Decay

Abstract

We perform a global analysis of the b → cτν data using the recent lattice results on the B c → J/ψ 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(Λ c ) and imposing the relaxed constraint B(B c → J/ψ) < 30% in light of the recent studies on LEP1 data and B c lifetime. We give predictions for the experimental observables including R(J/ψ), P τ (J/ψ), F L (J/ψ) and A FB (J/ψ) as well as their q 2 distribution in new physics scenarios/models. Our results suggest that the longitudinal τ polarization fraction P τ (J/ψ) and the forward-backward asymmetry A FB (J/ψ) are useful for testing the R 2 leptoquark model.

Next-to-leading order QCD calculation of $B_c$ to charmonium tensor form factors

“…We have confirmed their results of the form factors in the paper [44]. In addition, we also obtained the NLO QCD correction to B c → J/ψ tensor form factors T 1,2,3 , which are important input to precisely study the R(J/ψ) anomaly [54]. The method may also apply in the transition of double heavy diquark system [55].…”

Relations among Bc → J/ψ, ηc form factors

“…Other QCD-based computations employ QCD sum rules in the low q 2 range [14,15]. In the same kinematical range, using standard NRQCD methods the J/ψ|cΓ i b|B c matrix elements are expressed in the form J/ψ|cΓ i b|B c ψ Bc (0)ψ J/ψ (0)T i , in terms of meson wave functions at the origin ψ Bc (0), ψ J/ψ (0), and of perturbatively calculable hard-scattering kernels T i describing spectator interaction corrections and vertex corrections to factorization [16][17][18][19][20]. Perturbative QCD calculations use an analogous principle [21][22][23][24].…”