Neutrino dipole portal at electron colliders

TL;DR

This paper explores the potential of electron colliders like BESIII, Belle II, and STCF to detect heavy neutral leptons via a dipole portal, setting new constraints on neutrino magnetic moments across a range of masses.

Contribution

It introduces a novel search method for sterile neutrinos through monophoton signatures at electron colliders, focusing on the dipole portal interaction.

Findings

BESIII, Belle II, and STCF can probe dipole moments down to 1.3×10^{-5}, 8×10^{-6}, and 1.3×10^{-6} GeV^{-1} respectively.

The colliders can explore previously untested parameter space for neutrino masses from dozens to thousands of MeV.

Constraints on muon-neutrino dipole moments are also improved with these experiments.

Abstract

We propose to search for a heavy neutral lepton (HNL), that is also know as sterile neutrino, in electron colliders running with the center-of-mass energies at few GeV, including BESIII, Belle II, and the proposed Super Tau Charm Factory (STCF). We consider the HNL interacting with Standard Model neutrino and photon via a transition magnetic moment, the so-called dipole portal.We use the monophoton signature at electron colliders to probe the constraints on the active-sterile neutrino transition magnetic moments $d$ as the function of the HNL's mass $m_N$.It is found that BESIII, Belle II and STCF can probe the upper limits for $d$ down to 1.3 $\times 10^{-5}\ {\rm GeV}^{-1}$, 8 $\times 10^{-6}\ {\rm GeV}^{-1}$, and 1.3 $\times 10^{-6}\ {\rm GeV}^{-1}$ with $m_N$ around GeV scale, respectively, and have sensitivity to the previously unexplored parameter space for electron- ($d_e$) and tau-neutrino ($d_\tau$) dipole portal with $m_N$ from dozens to thounsands MeV. On $d_\mu$ for HNL mixing with the {muon}-neutrino, Belle II and STCF can also provide leading constraints.