A detailed analysis of possible new-physics effects in semileptonic decays $B_s \to D_s^{(*)}τ\barν$

Abstract

We study the semileptonic decays $B_s \to D_s^{(*)}τ\barν$ as a promising probe for new physics (NP) beyond the standard model (SM). The extension of the SM is done through the introduction of four-fermion operators beyond the $V-A$ structure with the corresponding Wilson coefficients characterizing their contribution. The constraints on these coefficients are obtained from recent experimental data. Form factors describing hadron transitions are calculated in our covariant quark model with infrared confinement. Theoretical predictions for the full set of observables in these channels are provided. We analyze possible NP effects to be tested in future experiments.

Figures (15)

• Figure 1: One-loop self-energy diagram for a meson.
• Figure 2: Form factors of the transitions $B_s\to D_s$ (upper panels) and $B_s \to D_s^*$ (lower panels).
• Figure 3: $1\sigma$ constraints on the complex Wilson coefficients from experimental data of $R_D$, $R_{D^*}$, $R_{J/\psi}$, and $F_L^{D^*}$. The dashed curves represent the upper limits $\mathcal{B}(B_c\to\tau\bar{\nu}_\tau)\leq 10\%$ (smaller) and $\mathcal{B}(B_c\to\tau\bar{\nu}_\tau)\leq 30\%$ (larger). For $V_L$ and $V_R$, we show only the limit $\mathcal{B}(B_c\to\tau\bar{\nu}_\tau)\leq 10\%$. For $T_L$, $\mathcal{B}(B_c\to\tau\bar{\nu}_\tau)$ has no effect.
• Figure 4: The allowed regions for the complex Wilson coefficients obtained from experimental data of $R_D$, $R_{D^*}$, $R_{J/\psi}$, and $F_L^{D^*}$ within $2\sigma$, and from the constraint $\mathcal{B}(B_c\to\tau\bar{\nu}_\tau)\leq 30\%$. Best-fit values are indicated by asterisks.
• Figure 5: Definition of the angles $\theta$, $\theta^\ast$, and $\chi$ in the cascade decay $\bar{B}^0_s\to D^{\ast+}_s(\to D^+_s\pi^0)\tau^-\bar{\nu}_\tau$.