Search for sterile neutrinos at the DANSS experiment

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~$\mathrm{G}{\mathrm{W}}_{\mathrm{th}}$ 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 $\tilde{\hat{I}}{½}_e$ per day at the closest position with the cosmic background less than 3$\%$. The inverse beta decay process is used to detect $\tilde{\hat{I}}{½}_e$. Sterile neutrinos are searched for assuming the $4\hat{I}½$ model (3 active and 1 sterile $\hat{I}½$). The exclusion area in the $\hat{I}”m_{14}^2,{\sin }^{2}2\hat{I}{¸}_{14}$ 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 $\tilde{\hat{I}}{½}_e$ 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 ${\sin }^{2}2\hat{I}{¸}_{14}<0.01$ in the most sensitive region.

10 pages, 13 figures, version accepted for publication