A quantitative study on helicity inversion in Majorana neutrino decays at the LHC
Richard Ruiz
We report an analytical and numerical investigation into the impact of helicity inversion in LHC processes that do not conserve lepton number. As a case study, we focus on the production and decay of Majorana neutrinos through W bosons in the Phenomenological Type I Seesaw model. Using the Monte Carlo event generator MadGraph5_aMC@NLO in conjunction with the HeavyN model libraries, we perform exact matrix element (ME) computations without the narrow width approximation. Despite helicity inversion appearing explicitly in MEs, we report the absence of helicity suppression in collider observables for 1→4 and 2→4 processes. We attribute this incongruity to the different scalings of 4-momenta and squared 4-momenta in MEs and squared MEs, with the latter leading to exact cancelations in the on-shell limit. Implications for other scenarios are discussed.