Four Fold Angular Decay Distribution of Λb Decay

Abstract

This thesis addresses the semi leptonic decay process of Λb → Λ(→ Nπ)l +l − using Λb as unpolarized baryon. The hamiltonian for the decay is derived using the framework of Operator Product Expansion (OPE) that splits the problem into short- and long-distance physics. The Standard Model (SM) operator basis are utilized along with the chirality flipped basis, which are relevant for the contribution to physics beyond the Standard Model. The four fold differential decay distribution is expressed in term of the ten angular observables. The short-distance physics is defined by Wilson coefficients, which are computed within the SM using perturbative Quantum Chromodynamics (QCD) using loop diagrams, whereas long-distance physics requires matrix elements of the local operators, which are derived using non-perturbative QCD methods, particularly lattice QCD. We obtain the four-fold differential decay width for the process in two steps: first, by analyzing the Λb → Λl +l − transition, and then by studying the Λ(→ Nπ) decay. This hadronic matrix elements for Λb → Λ and Λ → N transition are defined in the helicity basis and they are written in terms of the hadronic form factors. For the later part of the decay process two independent hadronic form factors appear while for the former part of the decay ten independent form factor appear. For numerical analysis the values of the form factors are taken from the lattice QCD predictions. The new physics Wilson coefficients information is collected from current literature and the data is taken from the global fit analysis with best fit values for the vector and the axial vector scenarios of the Wilson coefficients. Finally, we predict various observables for the decay channel in both the Standard Model and the two new physics scenarios along with their comparison with the experimental predictions.