Statistical data analysis in the DANSS experiment

Abstract

DANSS is a one cubic meter highly segmented solid scintillator detector. It is placed under a 3.1 GW industrial reactor at the Kalinin NPP (Russia) on a movable platform. The distance from the reactor core center is varied from 10.7 m to 12.7 m on-line. The inverse beta decay (IBD) process is used to detect antineutrinos. DANSS detects about 5000 IBD events per day.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. Therefore, results do not depend on the shape and normalization of the reactor spectrum, as well as on the detector efficiency. The excluded area covers a wide range of the sterile neutrino parameters up to sin2 2θ14 < 0.01 in the most sensitive region. The Reactor Antineutrino Anomaly optimum point is excluded with a confidence level higher than 5σ. A Gaussian CLs method was used to obtain exclusion areas. CLs method includes a point from sin2 2θ, Δm2 plane into exclusion area only if the experiment sensitivity to such point is good. Details of this approach are presented.