# Search for Heavy Sterile Neutrinos in Trileptons at the LHC

## TL;DR

This paper proposes a new search strategy at the LHC for heavy sterile neutrinos using trilepton final states, demonstrating improved detection and discrimination capabilities between Dirac and Majorana types with advanced analysis methods.

## Contribution

It introduces a combined Cut-and-Count and Multi-Variate Analysis approach for sterile neutrino detection and discrimination at the LHC, enhancing sensitivity over traditional methods.

## Key findings

- MVA method significantly improves discovery limits.
- Sterile neutrinos detectable at 5σ with mixings around 10^{-6}.
- Discrimination between Dirac and Majorana neutrinos feasible at mixings of 10^{-5}.

## Abstract

We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of $W^\pm \to e^\pm e^\pm \mu^\mp \nu$ and $\mu^\pm \mu^\pm e^\mp \nu$ at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass $m_N = 20$ GeV and 50 GeV are tested. For an integrated luminosity of 3000 ${\rm fb}^{-1}$, sterile neutrinos can be found with $5 \sigma$ significance if heavy-to-light neutrino mixings $|U_{Ne}|^2 \sim |U_{N\mu}|^2\sim 10^{-6}$, while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order $10^{-5}$.