Heavy neutrinos at future linear e$^+$e$^-$ colliders

TL;DR

This paper investigates the potential to detect heavy neutrinos at future linear e$^+$e$^-$ colliders, providing new sensitivity estimates that surpass current experimental limits for neutrino-lepton couplings.

Contribution

It presents the first detailed analysis of heavy neutrino detection prospects at future linear colliders, with improved sensitivity estimates over existing bounds.

Findings

Future colliders can probe neutrino-lepton couplings down to 10^{-7} - 10^{-6}.

Limits at future colliders are more stringent than current LHC and other collider bounds.

Heavy neutrinos with masses up to 3.2 TeV could be observed or constrained.

Abstract

Neutrinos are among the most mysterious particles in nature. Their mass hierarchy and oscillations, as well as their antiparticle properties, are being intensively studied in experiments around the world. Moreover, in many models of physics beyond the Standard Model, the baryon asymmetry or the dark matter density in the Universe are explained by introducing new species of neutrinos. Among others, heavy neutrinos of Dirac or Majorana nature were proposed to solve open questions in High Energy Physics. Such neutrinos with masses above the EW scale could be produced at future linear e$^+$e$^-$ colliders, like the Compact LInear Collider (CLIC) or the International Linear Collider (ILC). We studied the possibility of observing decays of heavy Dirac and Majorana neutrinos in the $qq\ell$ final state with ILC running at 500 GeV and 1 TeV, and CLIC at 3 TeV. The analysis is based on the Whizard event generation and fast simulation of detector response with Delphes. Neutrinos with masses from 200 GeV to 3.2 TeV were considered. We estimated the limits on the production cross sections, interpreted them in terms of the neutrino-lepton coupling parameter $V_{\ell N}^{2}$ (effectively the neutrino mixing angle) and compared them with current limits coming from the LHC running at 13 TeV, as well as the expected limits from future hadron colliders. The limits for the future lepton colliders, extending down to the coupling values of $10^{-7} - 10^{-6}$, are stricter than any other limit estimates published so far.