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

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.

Comments: 18 pages, 10 captioned figures, and 7 tables