Abstract
We study the differential decay rate for the rare Λ b → Λ(→ Nπ)ℓ + ℓ − transition, including a determination of the complete angular distribution, assuming unpolarized Λ b baryons. On the basis of a properly chosen parametrization of the various helicity amplitudes, we provide expressions for the angular observables within the Standard Model and a subset of new physics models with chirality-flipped operators. Hadronic effects at low recoil are estimated by combining information from lattice QCD with (improved) form-factor relations in Heavy Quark Effective Theory. Our estimates for large hadronic recoil — at this stage — are still rather uncertain because the baryonic input functions are not so well known, and non-factorizable spectator effects have not been worked out systematically so far. Still, our phenomenological analysis of decay asymmetries and angular observables for Λ b → Λ(→ Nπ)ℓ + ℓ − reveals that this decay mode can provide new and complementary constraints on the Wilson coefficients in radiative and semileptonic b → s transitions compared to the corresponding mesonic modes.
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Böer, P., Feldmann, T. & van Dyk, D. Angular analysis of the decay Λ b → Λ(→ Nπ)ℓ + ℓ − . J. High Energ. Phys. 2015, 155 (2015). https://doi.org/10.1007/JHEP01(2015)155
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DOI: https://doi.org/10.1007/JHEP01(2015)155