Ξ_b → ${\Xi }_{c} \tau \bar {\nu }_{\tau }$ Decay in New Physics Models

Abstract

Motivated by several hints of lepton flavor universality (LFU) violation in $b\to c\tau \bar {\nu }_{\tau }$ transitions, we investigate the baryonic semi-leptonic Ξ_b → ${\Xi }_{c} \tau \bar {\nu }_{\tau }$ decay in Supersymmetry with R-parity violation (RPV SUSY) model and $W^{\prime }$ model. Using the parameter space of these two new physics (NP) models constrained from the up-to-date experimental data, we calculate the branching ratio ${\mathscr{B}}\left ({\Xi }_{b} \to {\Xi }_{c}\tau \bar {\nu }_{\tau }\right )$ and the integrated ratio $R_{{\Xi }_{c}}$, and also show the effects of these two NP models on some observables, such as the differential branching ratio $\frac {d{\mathscr{B}}}{dq^{2}}({\Xi }_{b} \to {\Xi }_{c}\tau \bar {\nu }_{\tau })$, the differential ratio $R_{{\Xi }_{c}}\left (q^{2}\right )$, the lepton-side forward-backward asymmetry $A_{FB}\left (q^{2}\right )$, the convexity parameter $C_{F}^{\tau }\left (q^{2}\right )$, the longitudinal polarizations $P_{L}^{\tau }\left (q^{2}\right )$ and $P_{L}^{{\Xi }_{c}}\left (q^{2}\right )$. We find that: (i) Comparing the SM predictions, ${\mathscr{B}}({\Xi }_{b} \to {\Xi }_{c}\tau \bar {\nu }_{\tau })$ and $R_{{\Xi }_{c}}$ can be enhanced by about 3σ level in the $W^{\prime }$ model, respectively. (ii) Both $\frac {d{\mathscr{B}}}{dq^{2}}({\Xi }_{b} \to {\Xi }_{c}\tau \bar {\nu }_{\tau })$ and $R_{{\Xi }_{c}}\left (q^{2}\right )$ can be enhanced significantly by the $W^{\prime }$ model effects, but for $A_{FB}\left (q^{2}\right )$, $C_{F}^{\tau }\left (q^{2}\right )$, $P_{L}^{\tau }\left (q^{2}\right )$ and $P_{L}^{{\Xi }_{c}}\left (q^{2}\right )$, these two NP models have no effects on these observables, since these two NP models do not generate new operators beyond the SM ones.