Final taus and initial state polarization signatures from effective interactions of Majorana neutrinos at future $e^{+}e^{-}$ colliders

Abstract

We study the possibility of future e + e − colliders to disentangle different new physics contributions to the production of heavy sterile Majorana neutrinos in the lepton number violating channel e + e − → l + l + +4jets, with l = e, µ, τ . This is done investigating the final anti-tau polarization trails and initial beam polarization dependence of the signal on effective operators with distinct Dirac-Lorentz structure contributing to the Majorana neutrino production and decay, which parameterize new physics from a higher energy scale. We find both analyses could well disentangle possible vectorial and scalar operators contributions.

Angular and polarization observables for Majorana-mediated B decays with effective interactions

“…In the case where one or two of the final leptons are tau leptons, we would like to see if a measurement of their polarization could give a hint on the kind of new physics involved in the production or decay of the intermediate N . As we will see, the polarization of the final taus in these decays could be used to distinguish the vectorial and scalar operators contributions to the N production and decay vertices, complementing those proposed for a higher m N scale in [36].…”

“…Our group has studied the Majorana N decays [30,31] and phenomenology mostly in colliders for masses m N above the EW-scale [32][33][34][35][36] focusing on LNV processes, and in the order 1 − 10 GeV scale, where its decay is dominated by the N → νγ channel [37], which was also considered in [38].…”

Majorana neutrinos with effective interactions in B decays

“…As we found in Sect. II, the B → µ − N effective decay depends on the couplings appearing in the vectorial (A V ) and scalar (A S ) interactions in (17), the N → µ − π + depends on the C V and C S couplings in (19) and the N → νγ depends on the one-loop tensorial couplings in (10).…”

“…Other observables involving the final photon or charged lepton polarizations could improve also the sensitivity to the different contributions from vectorial and scalar operators. As we recently explored in [19], the study of final tau polarizations for the B → τ νγ decay could help disentangle vectorial and scalar contributions in the intermediate production process…”

“…scale and parametrized at low energies by a model independent effective Lagrangian. In this approach, we consider that the sterile N interacts with the SM particles by higher dimension effective operators, taking these interactions to be dominant in comparison with the mixing with light neutrinos through the Yukawa couplings, which we neglect [12][13][14][15][16][17][18][19]. We depart from the usual viewpoint in which the mixing with the standard neutrinos is assumed to govern the N production and decay mechanisms.…”