Angular Analysis of the Decay $Î_b \to Î(\to N Ï) \ell^+\ell^-$
arXiv:1410.2115 · doi:10.1007/JHEP01(2015)155
Abstract
We study the differential decay rate for the rare $Î_b \to Î(\to N Ï)\ell^+\ell^-$ transition, including a determination of the complete angular distribution, assuming unpolarized $Î_b$ 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 $Î_b \to Î(\to N Ï)\ell^+\ell^-$ reveals that this decay mode can provide new and complementary constraints on the Wilson coefficients in radiative and semileptonic $b \to s$ transitions compared to the corresponding mesonic modes.
31 pages, 1 figure; v2 as published: add numerical study of optimized observables in the SM and two benchmark scenarios, conclusions unchanged; v3: fixed typo in eq. (3.28), conclusions unchanged