Search for heavy neutrinos mixing with tau neutrinos

TL;DR

This paper reports a search for heavy neutrinos mixing with tau neutrinos using data from the NOMAD detector, setting new upper limits on the mixing strength in the 10-190 MeV mass range and constraining related theoretical models.

Contribution

It provides the first experimental upper limits on heavy neutrino mixing with tau neutrinos in the 10-190 MeV mass range based on NOMAD data.

Findings

No candidate events observed, consistent with background expectations.

Established upper limits on heavy neutrino mixing strength.

Constrained interpretations of the KARMEN1 time anomaly.

Abstract

We report on a search for heavy neutrinos ($\nus$) produced in the decay $D_s\to \tau \nus$ at the SPS proton target followed by the decay $\nudecay$ in the NOMAD detector. Both decays are expected to occur if $\nus$ is a component of $\nu_{\tau}$.\ From the analysis of the data collected during the 1996-1998 runs with $4.1\times10^{19}$ protons on target, a single candidate event consistent with background expectations was found. This allows to derive an upper limit on the mixing strength between the heavy neutrino and the tau neutrino in the $\nus$ mass range from 10 to 190 $\rm MeV$. Windows between the SN1987a and Big Bang Nucleosynthesis lower limits and our result are still open for future experimental searches. The results obtained are used to constrain an interpretation of the time anomaly observed in the KARMEN1 detector.\