13 October 2025 – We present a new paper with the title ‘‘Search for an eV-scale sterile neutrino with the first six detection units of KM3NeT/ORCA“.
Sterile neutrinos are hypothetical neutrinos proposed by theoretical physicists to explain unexpected experimental results obtained over the course of the past 25 years. They are named sterile to distinguish them from the known neutrinos in the Standard Model. However, the existence of sterile neutrinos has not yet been experimentally confirmed. In this paper we present the results of the first search for sterile neutrinos with our ORCA detector.
ORCA is designed for studies of neutrino oscillations. Sterile neutrinos are expected to have an effect on the first νμ → ν𝜏 oscillation maximum. By examining this expected impact we could constrain the magnitude of the mixing of both muon- and tau- neutrinos with an eV-scale sterile neutrino state.
For the search we used data collected from January 2020 to November 2021 with the first six detection units of the ORCA – about 5% of the full detector. Our data sample contains 5828 neutrino candidates.
Despite the relatively small detection volume of ORCA6 and the limited statistics, we already obtained limits on the relevant parameters for mixing with a sterile neutrino state, which are competitive with the results reported by other experiments. It indicates that with an increasing detection volume of ORCA it is possible to crucially contribute to sterile neutrino searches in the coming years.
The paper has been submitted to Journal of High Energy Physics and is available as a preprint at arXiv: 2510.07360
In the figure the upper limits at 90% CL on mixing parameters obtained with ORCA6 are compared with the results of other experiments. The excluded regions are on the top right side of the contours.
