Production of Like Sign Di-Leptons in p-p Collisions Through Composite Majorana Neutrinos

TL;DR

This paper investigates the potential for detecting composite Majorana neutrinos through like-sign di-lepton production at the LHC, providing detailed calculations and comparing sensitivities with neutrinoless double beta decay experiments.

Contribution

It introduces a detailed tree-level amplitude calculation for like-sign di-lepton production via composite Majorana neutrinos at the LHC, including interference effects and kinematic cuts.

Findings

LHC can exclude composite Majorana neutrinos up to 850 GeV.

Certain parameter regions yield signals above Standard Model background.

LHC sensitivity is comparable to neutrinoless double beta decay experiments.

Abstract

The production of Like-Sign-Di-leptons (LSD), in the high energy lepton number violating ($\Delta L = +2$) reaction, p p --> 2jets + l+l+ (l=e,\mu,\tau) of interest for the experiments to be performed at the forthcoming Large Hadron Collider (LHC), is investigated in detail, taking up a composite model scenario in which the exchanged virtual composite neutrino is assumed to be a Majorana particle that couples to the light leptons via the $SU(2)\times U(1)$ gauge bosons through a magnetic type coupling ($\sigma_{\mu\nu}$). An helicity projection method is used to evaluate exactly the tree-level amplitudes of the contributing parton subprocesses ($2\to 4$), which allows to take into account all exchange diagrams and occurring interferences. Numerical estimates of the corresponding signal cross-section that implement kinematical cuts needed to suppress the Standard Model background, are presented which show that in some regions of the parameter space the total number of LSD events is well above the background. Assuming non-observation of the LSD signal it is found that LHC would exclude a composite Majorana neutrino up to 850 GeV (if one requires 10 events for discovery). The sensitivity of LHC experiments to the parameter space is then compared to that of the next generation of neutrinoless double beta decay ($\beta\beta_{0\nu}$) experiment, GENIUS, and it is shown that they will provide constraints of the same order of magnitude and will play a complementary role.