Unraveling New Physics Effects in $b \rightarrow s \ell_1 \ell_2$ Transitions with a Model-Independent Perspective

TL;DR

This paper investigates lepton flavor-violating $b ightarrow s \, ext{lepton}_1 \, ext{lepton}_2$ decays using a model-independent approach, deriving angular distributions and providing bounds to guide future experimental searches for new physics.

Contribution

It introduces a comprehensive, model-independent analysis of LFV $b ightarrow s \, ext{lepton}_1 \, ext{lepton}_2$ decays, including baryonic modes, with predictions for observables and experimental bounds.

Findings

Derived angular distributions for LFV decays.

Provided bounds on branching ratios, asymmetries, and polarization.

Estimated sensitivities for future experiments like LHCb upgrade and Belle II.

Abstract

Motivated by recent anomalies in observables associated with flavor-changing neutral current (FCNC) transitions, specifically $b \rightarrow s \ell^+ \ell^-$ processes, we present a comprehensive analysis of lepton flavor-violating (LFV) decay modes mediated by $b \rightarrow s \ell_1 \ell_2$ transitions with $\ell_1 \neq \ell_2$. While such LFV processes are forbidden within the Standard Model (SM), they naturally arise in several of its extensions, including models featuring additional vector-like fermions and extra $Z'$ bosons. Employing the most general effective Hamiltonian for $b \rightarrow s \ell_1 \ell_2$ transitions, we derive the angular distributions of the relevant decay modes. Adopting a model-independent framework, we systematically study the LFV decays $B \rightarrow K^* \ell_1 \ell_2$, $B_s \rightarrow \phi \ell_1 \ell_2$, $B \rightarrow K_2^* \ell_1 \ell_2$, and $\Lambda_b \rightarrow \Lambda \ell_1 \ell_2$. Although LFV mesonic decays have been widely explored, the corresponding baryonic decays remain comparatively under-investigated. We provide bounds on branching ratio ($\mathcal{B}$), forward-backward asymmetry ($\mathcal{A}_{FB}$), and longitudinal lepton polarization fraction ($\mathcal{F}_L$). Furthermore, considering the projected sensitivities of the LHCb upgrade and Belle II experiments, we estimate upper limits for these observables, offering promising avenues for probing new physics in these LFV channels.