Speaker
Description
We propose to search for a heavy neutral lepton (HNL), that is also
known 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 $1.3 \times 10^{-5}\
\text{GeV}^{-1}$, $8 \times 10^{-6}\ \text{GeV}^{-1}$, and $1.3 \times
10^{-6}\ \text{GeV}^{-1}$ 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 thousands MeV. On $d_{\mu }$ for HNL mixing
with the $\mu$-neutrino, Belle II and STCF can also provide leading
constraints.
