Monojet search for heavy neutrinos at future $Z$-factories

TL;DR

This paper explores the potential of future Z-factories to detect heavy neutrinos in the 3-15 GeV mass range through monojet signatures, filling a gap between existing experimental sensitivities.

Contribution

It introduces a novel monojet search strategy at future Z-factories for heavy neutrinos in the 3-15 GeV range, utilizing jet substructure analysis to improve detection.

Findings

Monojet signals are promising for heavy neutrino detection in the 3-15 GeV range.

Jet substructure analysis enhances signal reconstruction and background suppression.

Upper bounds on cross section and mixing parameters are established.

Abstract

The existence of heavy neutrinos is the most prominent feature of type-I seesaw-like mechanisms, which naturally explain tiny masses of observed neutrinos. Various experiments have been conducted to search for heavy neutrinos, with meson decays sensitive to heavy neutrinos lighter than $B$ mesons and high energy collider experiments sensitive to the ones with masses larger than $\mathcal{O}(0.1)$ TeV. In between, there is a mass gap uncovered by these two kinds of experiments, and by this work, we investigate the 3-15 GeV neutrino searches at future $Z$-factories via the process $e^{-}e^{+}\rightarrow Z \rightarrow \nu N \rightarrow \nu \ell\bar{q}q'$ with $\ell=e,\mu$. Based on the simulation of signal and background events, we find that the signals appear as monojet events owning to the large Lorentz boost of the heavy neutrinos. Furthermore, the substructures of such monojet are essential to reconstruct the signal and suppress the background. The upper bounds on the cross section of the signal process and the mixing parameter ${| V_{\ell N}|}^2$ are obtained. Compared with other experiments, the monojet method at future $Z$-factories will be able to fill the gap around this mass range.