Not-that-heavy Majorana neutrino signals at the LHC

Abstract

We consider the possibility of Majorana neutrinos production at the Large Hadron Collider (LHC) by studying the $pp \rightarrow l_i^{+} l_j^{+} +2~jets$ ($l_j\equiv e ,\mu$) process which, due to leptonic number violation, is a clear signature for intermediate Majorana neutrino contributions. The interactions between Majorana neutrinos and the Standard Model particles are obtained from an effective lagrangian approach. Majorana neutrinos with masses of a few $GeV$ are long-lived neutral particles, and we take advantage of its measurable decay length: in the same-sign dilepton channel, we exploit this fact imposing cuts that reject the $SM$ background, and analyze the distribution corresponding to the angle between the final leptons, using a forward-backward asymmetry to study the effects of the different gauge invariant operators. We also study the $pp\rightarrow l_i^+ \nu \gamma$ process, which is dominant for low $m_N$ masses if tensorial one-loop generated new physics contributions are present. This channel could be observed at the LHC with the aid of non-pointing photons observables and cuts on the displacement between the prompt lepton and the photon.