Search for sterile neutrinos at the DANSS experiment

TL;DR

The DANSS experiment searches for sterile neutrinos by analyzing antineutrino spectra at different distances from a nuclear reactor, setting new exclusion limits on sterile neutrino parameters with high statistical significance.

Contribution

This study provides the first high-statistics search for sterile neutrinos using a segmented detector at multiple distances, improving exclusion limits in the $ u$-mass and mixing parameter space.

Findings

Excluded a wide range of sterile neutrino parameters up to $ ext{sin}^2 2 heta_{14}<0.01$

Collected 966,000 antineutrino events at three distances

Results are independent of reactor spectrum shape and detector efficiency

Abstract

DANSS is a highly segmented 1~m${}^3$ plastic scintillator detector. Its 2500 one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS detector is placed under an industrial 3.1~$\mathrm{GW_{th}}$ reactor of the Kalinin Nuclear Power Plant 350~km NW from Moscow. The distance to the core is varied on-line from 10.7~m to 12.7~m. The reactor building provides about 50~m water-equivalent shielding against the cosmic background. DANSS detects almost 5000 $\widetilde\nu_e$ per day at the closest position with the cosmic background less than 3$\%$. The inverse beta decay process is used to detect $\widetilde\nu_e$. Sterile neutrinos are searched for assuming the $4\nu$ model (3 active and 1 sterile $\nu$). The exclusion area in the $\Delta m_{14}^2,\sin^22\theta_{14}$ plane is obtained using a ratio of positron energy spectra collected at different distances. Therefore results do not depend on the shape and normalization of the reactor $\widetilde\nu_e$ spectrum, as well as on the detector efficiency. Results are based on 966 thousand antineutrino events collected at 3 distances from the reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to $\sin^22\theta_{14}<0.01$ in the most sensitive region.