Abstract
DANSS is a highly segmented 1 m3 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 GWth 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 ν˜e per day at the closest position with the cosmic background less than 3%. The inverse beta decay process is used to detect ν˜e. Sterile neutrinos are searched for assuming the 4ν model (3 active and 1 sterile ν). The exclusion area in the Δm142,sin22θ14 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 ν˜e spectrum, as well as on the detector efficiency. Results are based on 966 thousand antineutrino events collected at three different distances from the reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to sin22θ14<0.01 in the most sensitive region.
Highlights
Oscillations of the three neutrino flavors are well established
Additional light active neutrinos are excluded by the measurements of the Z boson decay width [2]
Indications of several effects observed with about 3σ significance level can be explained by active-sterile neutrino oscillations
Summary
Oscillations of the three neutrino flavors are well established. Two mass differences and three angles describing such oscillations have been measured [1]. The GALEX and SAGE Gallium experiments performed calibrations with radioactive sources and reported the ratio of numbers of observed to predicted events of 0.88 ± 0.05 [3] This deficit is the so called “Gallium anomaly” (GA) [4]. Mueller et al [5] made new estimates of the reactor νe flux which is about 6% higher than experimental measurements at small distances This deficit is the so called “Reactor antineutrino anomaly” (RAA). Preprint submitted to Elsevier anomalies can be explained by active-sterile neutrino oscillations at very short distances requiring a mass-squared difference of the order of 1 eV2 [6]. The existence of sterile neutrinos would manifest itself in distortions of the νe energy spectrum at short distances. The most reliable way to observe such distortions is to measure the νe spectrum with the same detector at different distances.
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