Angular observables and branching ratio for $B_s\to φ\ell^+ \ell^-$ decay

TL;DR

This work addresses the SM prediction and phenomenology of the rare decay $B_s \to \phi \ell^+ \ell^-$. The authors compute the $B_s \to \phi$ transition form factors within the covariant confined quark model and use them to derive the branching fractions and a complete set of angular observables across $q^2$, incorporating NNLL corrections to the Wilson coefficients. They present detailed predictions for the differential branching, $F_L$, $A_{FB}$, and optimized angular observables $P_i$ and $S_i$, and compare with LHCb data and PQCD results, finding general agreement with data and highlighting the importance of NNLL effects at low $q^2$. The study provides a consistent SM baseline within CCQM for $B_s \to \phi \ell^+ \ell^-$ and informs future precision tests and potential new-physics interpretations.

Abstract

In this paper, an analysis of the $B_s\to φ\ell^+ \ell^-$ rare decay is presented within the framework of the covariant confined quark model. The $B_s\to φ$ transition form factors are calculated and then used to compute the branching fractions and angular observables in various $q^2$ bins, including the forward-backward asymmetry $A_{FB}$, the longitudinal polarization $F_L$, and the optimized observables $A_i$ and $S_i$. The results show agreement with the latest experimental data given by LHCb collaboration and compared with available theoretical predictions.

Figures (6)

• Figure 1: The behavior of the differential branching fraction ${\cal B}(B_{s} \to \phi \ell^+ \ell^-)$.
• Figure 2: Forward-backward asymmetry $A_{FB}$.
• Figure 3: Longitudinal polarization $F_L$.
• Figure 4: The behavior of the differential branching fraction ${\cal B}(B_{s} \to \phi \nu \bar{\nu})$.
• Figure 5: Observables $A_{i}$ and $S_{i}$ for $B_s\to\phi \mu^+\mu^-$ decay.