Abstract
We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to c\tau\nu$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.
Highlights
The Bc meson is the lowest bound state of two heavy quarks of different flavors, lying below the BDthreshold
We focus on the tau mode of these decays, which may provide some hints of new physics effects
In the wake of recent measurements of the Bc weak decays performed by the LHCb Collaboration, we have studied possible new physics (NP) effects in the semileptonic decays Bc → J=ψτν and Bc → ηcτν based on an effective Hamiltonian consisting of vector, scalar, and tensor fourfermion operators
Summary
The Bc meson is the lowest bound state of two heavy quarks of different flavors, lying below the BDthreshold. Essential to the study of the Bc semileptonic decays is the calculation of the invariant form factors describing the corresponding hadronic transitions. The knowledge of the Bc → J=ψðηcÞ form factors is much less than that of the B 0 → DðÃÞ ones This is due to, first, the lack of experimental data for the decays Bc → J=ψðηcÞlν, and second, the appearance of two heavy quark flavors in the initial (bc) and final (cc) states. The hadronic helicity amplitudes H’s are written in terms of the invariant form factors defined in Eq (7) Their explicit expressions are presented in Ref. In the CCQM, we obtain the following values for these constants (all in MeV): fBc 1⁄4 489.3; f
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