The $$ {\Lambda}_b\to {\Lambda}^{\ast }(1520)\left(\to N\overline{K}\right){\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} $$ decay at low-recoil in HQET

Abstract

Abstract In this paper we discuss the Standard Model and new physics sensitivity of the $$ {\Lambda}_b\to {\Lambda}^{\ast }(1520)\left(\to N\overline{K}\right){\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} $$ Λ b → Λ ∗ 1520 → N K ¯ ℓ + ℓ − decay at low-recoil, where ℓ± are massive leptons and $$ N\overline{K}=\left\{{pK}^{-},n{\overline{K}}^0\right\} $$ N K ¯ = pK − n K ¯ 0 . We provide a full angular distribution with a set of operators that includes the Standard Model operators and their chirality flipped counterparts, and new scalar and pseudo-scalar operators. The resulting angular distribution allows us to construct observables that we study in the Standard Model and in model-independent new physics scenarios. To reduce the hadronic effects emanating from the Λb→ Λ* (1520) transition form factors, we exploit the Heavy Quark Effective theory framework valid at low Λ∗(1520) recoil, i.e., large dilepton invariant mass squared $$ {q}^2\sim \mathcal{O}\left({m}_b^2\right) $$ q 2 ∼ O m b 2 . Working to the leading order in 1/mb and including $$ \mathcal{O}\left({\alpha}_s\right) $$ O α s corrections, we compute the ‘improved Isgur-Wise relations’ between the form factors. The relations correlate the form factors and thereby allow the description of this decay at the low-recoil region with a smaller number of independent form factors.