Search for a heavy neutrino in $\tau$ decays at Belle

TL;DR

This study searches for heavy neutrinos in tau decays using Belle data, setting upper limits on their couplings in the 0.2-1.6 GeV/c^2 mass range, with no significant signals observed.

Contribution

First search for heavy neutrinos in tau decays at Belle, establishing new upper limits on their couplings in the specified mass range.

Findings

No significant heavy neutrino signals detected.

Set 90% CL upper limits on neutrino couplings.

Constrained heavy neutrino parameter space.

Abstract

We report on a search for a heavy neutrino in the decays $\tau^- \to \pi^- \nu_h$, $\nu_h \to \pi^\pm \ell-+$, $\ell = e, \mu$. The results are obtained using the full data sample collected with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. We observe no significant signal and set 90% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional SM left-handed neutrinos in the mass range 0.2-1.6 GeV/c$^2$.