A detailed study of the $\Lambda_b \to \Lambda \ell^+ \ell^-$ decays in the Standard Model

TL;DR

This paper analyzes the decay process b1_b b7 b1 in the Standard Model using lattice and LHCb data, fitting form factors, and predicting observables including lepton flavor universality ratios.

Contribution

It provides a comprehensive fit of decay form factors and predicts observables, including lepton flavor universality ratios, based on combined theoretical and experimental inputs.

Findings

No significant deviations from the Standard Model observed.

Predicted lepton flavor universality ratio R_{b1} consistent with current data.

Form-factor fits are stable across different scenarios.

Abstract

Based on the standard model (SM) of particle physics, we study the decays $\Lambda_b \to \Lambda \ell^+ \ell^-$ in light of the available inputs from lattice and the data from LHCb. We fit the form-factors of this decay mode using the available theory and experimental inputs after defining different fit scenarios and checking their consistencies. The theory inputs include the relations between the form-factors in heavy quark effective theory (HQET) and soft collinear effective theory (SCET) at the endpoints of di-lepton invariant mass squared $q^2$. Utilizing the fit results, we have predicted a few observables related to this mode. We have also predicted the observable $R_{\Lambda} = Br(\Lambda_b \to \Lambda \ell_i^+\ell_i^- )/Br(\Lambda_b \to \Lambda \ell_j^+\ell_j^-)$ where $\ell_{i}$ and $\ell_j$ are charged leptons of different generations ($i \ne j$). At the moment, we do not observe noticeable differences in the extracted values of the observables in fully data-driven and SM like fit scenarios.