Expanding the Reach of Heavy Neutrino Searches at the LHC

TL;DR

This study explores the potential of vector boson fusion processes at the 13 TeV LHC to search for heavy Majorana neutrinos, showing improved sensitivity and extended mass reach compared to traditional methods.

Contribution

It demonstrates the effectiveness of VBF topology in searching for TeV-scale Majorana neutrinos, providing new strategies and expected bounds for LHC experiments.

Findings

VBF process surpasses Drell-Yan for neutrino masses above 1.4 TeV.

Expected exclusion bounds up to 2.4 TeV for 1000 fb$^{-1}$ data.

Significantly increased discovery potential with VBF topology at the LHC.

Abstract

The observation of neutrino oscillations establishes that neutrinos ($\nu_{\ell}$) have non-zero mass and provides one of the more compelling arguments for physics beyond the standard model (SM) of particle physics. We present a feasibility study to search for hypothetical Majorana neutrinos ($N_{\ell}$) with TeV scale masses, predicted by extensions of the SM to explain the small but non-zero $\nu_{\ell}$ mass, using vector boson fusion (VBF) processes at the 13 TeV LHC. In the context of the minimal Type-I seesaw mechanism (mTISM), the VBF $\ell N_{\ell}$ production cross-section surpasses that of the Drell-Yan process at approximately $m_{N_{\ell}} = 1.4$ TeV. We consider $\mu N_{\mu}$ and $\tau N_{\tau}$ production through VBF processes (e.g. $qq'\to \tau N_{\tau}qq'$), with subsequent $N_{\mu}$ and $N_{\tau}$ decays to $\mu jj$ and $\tau jj$, as benchmark cases to show the effectiveness of the VBF topology for $N_{\ell}$ seaches at the 13 TeV LHC. The requirement of a dilepton pair combined with four jets, two of which are identified as VBF jets with large separation in pseudorapidity and a TeV scale dijet mass, is effective at reducing the SM background. This criteria may provide expected exclusion bounds, at 95\% confidence level, of $m_{N_{\ell}} < 1.7$ ($2.4$) TeV, assuming $100$ (1000) fb$^{-1}$ of 13 TeV data from the LHC and mixing $|V_{\ell N_{\ell}}|^{2} = 1$. The use of the VBF topology to search for $m_{N_{\ell}}$ increases the discovery reach at the LHC, with expected significances greater than 5$\sigma$ (3$\sigma$) for $N_{\ell}$ masses up to 1.7 (2.05) TeV using 1000 fb$^{-1}$ of 13 TeV data from the LHC.