Search for an eV-scale sterile neutrino with the first six detection units of KM3NeT/ORCA

Abstract

The existence of an eV-scale sterile neutrino has been proposed to explain several anomalous experimental results obtained over the course of the past 25 years. The first search for such a sterile neutrino conducted with data from KM3NeT/ORCA -- a water Cherenkov neutrino telescope under construction at the bottom of the Mediterranean Sea -- is reported in this paper. GeV-scale atmospheric neutrino oscillations are measured by reconstructing the energy and arrival direction of up-going neutrinos that have traversed the Earth. This study is based on a data sample containing 5828 neutrino candidates collected with 6 detection units ($5\%$ of the complete detector), corresponding to an exposure of 433 kton-years. From the expected effect of an eV-scale sterile neutrino on the first ${\nu }_{\mu }\to {\nu }_{\tau }$ standard oscillation maximum, simultaneous constraints are put on the magnitude of the $U_{\mu 4}$ and $U_{\tau 4}$ mixing elements assuming $\Delta m_{41}^2\ge 1$ eV${}^2$. The results are compatible with the absence of mixing between active neutrinos and a sterile state, with $|U_{\mu 4}{|}^2<0.138$ and $|U_{\tau 4}{|}^2<0.076$ at a $90\%$ confidence level. Such constraints are compatible with the results reported by other long-baseline experiments, and indicate that with KM3NeT/ORCA it is possible to bring crucial contributions to sterile neutrino searches in the coming years.

arXiv comment23 pages, 6 figures; minor revisions following comments from referee

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