Angular distribution of polarised Λb baryons decaying to Λℓ+ℓ−

Abstract

Rare b → s + − flavour-changing-neutral-current processes provide important tests of the Standard Model of particle physics. Angular observables in exclusive b → s + − processes can be particularly powerful as they allow hadronic uncertainties to be controlled. Amongst the exclusive processes that have been studied by experiments, the decay Λ b → Λ + − is unique in that the Λ b baryon can be produced polarised. In this paper, we derive an expression for the angular distribution of the Λ b → Λ + − decay for the case where the Λ b baryon is produced polarised. This extends the number of angular observables in this decay from 10 to 34. Standard Model expectations for the new observables are provided and the sensitivity of the observables is explored under a variety of new physics models. At low-hadronic recoil, four of the new observables have a new short distance dependence that is absent in the unpolarised case. The remaining observables depend on the same short distance contributions as the unpolarised observables, but with different dependence on hadronic form-factors. These relations provide possibilities for novel tests of the SM that could be carried out with the data that will become available at the LHC or a future e + e − collider.

On the angular distribution of Λb → Λ(→ N π)τ +τ − decay

“…For our SM results, we agree 4 with [5] D Λ b → Λ hadronic matrix elements A convenient choice for the parametrization of the Λ b → Λ hadronic matrix elements is the so called helicty basis [7] in terms of which the matrix elements for the vector current is…”

“…On the other hand, if the polarization of the Λ b is accounted for, the number of observables that one can gain access to become more than three times than the unpolarized case [5] making this decay an unique test ground for the SM and searches for NP.…”

“…Recent SM analysis of Λ b → Λ(→ N π) + − with massive leptons can be found in refs. [5,19,20]. In this paper we present a full angular analysis of Λ b → Λ(→ N π) + − in the SM+NP operator basis where we consider the leptons to be massive and the Λ b to be unpolarized.…”

Model independent new physics analysis in $$\Lambda _b\rightarrow \Lambda \mu ^+\mu ^-$$ Λ b → Λ μ + μ - decay

“…[26][27][28][29][30][31][32][33]. The b → μ + μ − angular distributions for polarized b were recently worked out in [34]. In Ref.…”

A new angle on an old problem: helicity approach to neutron beta decay in the Standard Model

“…The analytical expressions for the NLO corrections can be found in Eqs. (50)(51)(52)(53)(54)(55)(56)(57) and Eqs. (62-63) and have been evaluated with the form factor values listed in Eqs.…”