Role of $B_c^{+}\to B_{s,d}^{(\ast )}\bar{\ell }\hat{I}{½}_{\ell }$ in the Standard Model and in the search for BSM signals

Abstract

The decays $B_c^{+}\to B_a\bar{\ell }\hat{I}{½}_{\ell }$ and $B_c^{+}\to B_a^{\ast }(\to B_a{\hat{I}}^3)\bar{\ell }\hat{I}{½}_{\ell }$, with $a=s,d$ and $\ell =e,\hat{I}¼$, are studied in the Standard Model (SM) and in the extension based on the low-energy Hamiltonian comprising the full set of dimension-$6$ semileptonic $c\to s,d$ operators with left-handed neutrinos. Tests of $\hat{I}¼/e$ universality are investigated using such modes. The heavy quark spin symmetry is applied to relate the relevant hadronic matrix elements and to exploit lattice QCD results on $B_c$ form factors. Optimized observables are selected, and the pattern of their correlations is studied to identify the effects of the various operators in the extended low-energy Hamiltonian.

LaTex, 15 pages, 17 figures. Figures and references added, version to appear in PRD