Not-that-heavy Majorana neutrino signals at the LHC

TL;DR

This paper explores the potential for detecting Majorana neutrinos at the LHC through specific lepton-number-violating processes, utilizing decay length measurements and novel observables to distinguish signals from background.

Contribution

It introduces an effective Lagrangian framework for Majorana neutrino interactions and proposes new analysis strategies using decay length and angular distributions to identify signals.

Findings

Long-lived Majorana neutrinos with GeV masses can be detected via displaced decay signatures.

Forward-backward asymmetry analysis helps differentiate Majorana signals from Standard Model background.

Displacement and non-pointing photon observables enhance detection prospects for low-mass neutrinos.

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.