Statistical data analysis in the DANSS experiment

Abstract

DANSS is a one cubic meter highly segmented solid scintillator detector. DANSS is placed under a 3.1 GW industrial reactor at the Kalininskaya NPP (Russia) on a movable platform. The distance from the reactor core center is varied from 10.9 m to 12.9 m on-line. The inverse beta decay (IBD) process is used to detect antineutrinos. DANSS detects about 5000 IBD events per day with the background from cosmic muons at the level of 2%. Sterile neutrinos are searched for assuming a 4 neutrino model (3 active and 1 sterile neutrino). The exclusion area in the sterile neutrino parameter plane is obtained using a ratio of positron energy spectra collected at different distances. New analysis that uses information about relative counting rates as well as changes in positron energy spectra shapes is described. We present recent results based on 3.5 million IBD events collected at 3 distances from detector to reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to sin2 2θ ee < 0.008 in the most sensitive region. The significance of the best-fit point in the parameters space is 1.5σ.