Delving into new physics in semileptonic $b\to c\tau \bar{\nu }$ transitions

Abstract

Recently, several indications of lepton non-universality observables have been perceived in semileptonic $B$ meson decay processes, both in the neutral-current ($b\to sll$) and charged-current ($b\to cl{\bar{\nu }}_l$) transitions. Influenced by these fascinating quotients, we examine the semileptonic decays involving the $b\to cl{\bar{\nu }}_l$ quark level transitions. We execute it through a model independent analysis in order to probe the nature of new physics. Taking into consideration the most general effective Hamiltonian, we scrutinize ${\Lambda }_b\to {\Lambda }_c\tau {\bar{\nu }}_{\tau }$, $B_c^{+}\to {\eta }_c{\tau }^{+}{\nu }_{\tau }$, and $B\to D^{\ast \ast }\tau {\bar{\nu }}_{\tau }$ (where $D^{\ast \ast }=\{D_0^{\ast },D_1^{\ast },D_1,D_2^{\ast }\}$ are the four lightest excited charm mesons) processes, in the presence of new physics. We perform a global fit to different sets of new coefficients, making use of the measurements on $R_D$, $R_{D^{\ast }}$, $R_{J/\psi }$, $P_{\tau }^{D^{\ast }}$ and the upper limit on Br($B_c^{+}\to {\tau }^{+}{\nu }_{\tau }$). We then inspect the effect of constrained new couplings on the branching ratios, forward-backward asymmetry parameters, lepton non-universality ratios (LNU), lepton and hadron polarization asymmetries of these decay modes.

Comments: 41 pages, 13 figures, 14 tables