Recent results from the DANSS experiment XXXI International Conference on Neutrino Physics and Astrophysics Nataliya Skrobova (nataliya.skrobobva@gmail.com) for the DANSS collaboration DANSS design JINST 11 (2016) no.11, P11011 ●DANSS – Detector of reactor AntiNeutrino based on Solid-state Scintillator ●Location: Kalinin Nuclear Power Plant (KNPP), 3.1 GW commercial reactor, 5∙1013 ν cm-2 s-1, 50 m w.e. overburden ●10.9 -12.9 m from the reactor core center, movement online ●Multilayer Cu + CHB + Pb + CHB passive shielding ●Two-layer muon veto on 5 sides ●2500 scintillator strips with Gd containing coating for neutron capture ●Light collection with 3 WLS fibers ●Central fiber read out with individual SiPM ●Side fibers from 50 strips make a bunch of 100 on a PMT cathode = Module ●Dedicated WFD-based DAQ system 2 of 50 modules Conclusions ●We fit the observed positron spectra using the sum of 4 isotopes (HM model) ● 238U and 241Pu fission fractions are fixed (corresponding to KNPP data), ● 235U fission fraction is free parameter ●Each measurement corresponds to ∼ 6-10 days of data taking (~1% stat. accuracy) Measurements of σ5/σ9 (σ8/σ9 and σ1/σ9 are taken from Huber Phys.Rev.C,84,024617 and Mueller Phys.Rev.C,83,054615) DANSS result σ5/σ9 = 1.54 ± 0.06 is larger than Day Bay Phys.Rev.Lett.120,022503 (1.445 ± 0.097) and agrees with Huber + Mueller (1.53 ± 0.05). Use of DB-Slope in our formula gives: σ5/σ9 = 1.459 ± 0.052 ⇒ difference between DANSS and Daya Bay is due to slope Searches for sterile neutrinos High energy neutrinos Measurements of absolute νe flux Experimental uncertainty without νe flux – 4% Observed to predicted ratio: 0.98±0.04 (HM model), 1.02±0.04 (KI model) DANSS results are consistent with both models within errors Total uncertainty in IBD rates (including νe flux) – 7% Systematic uncertainties (1σ): ●Energy scale (2%) and shift (50 keV) ●Energy resolution (additional smearing 6%/√E ⊕ 2%) ●Correlated backgrounds (35%) ●Distance to the fuel burning profile center (5 cm) ●Relative efficiencies (0.4%) Using current statistics we see no statistically significant evidence of 4ν signal (best point significance: ~2.0σ ) Exclusions are calculated using Gaussian CLs method ●DANSS analysis without absolute counting rates excludes a large and the most interesting fraction of sterile neutrino parameter space using only ratio of e+ spectra at 3 distances. ●Oscillation analysis with absolute counting rates (HM model) excludes practically all sterile parameter space preferred by BESTPhys.Rev.Lett.128,232501 and the best fit point of Neutrino-4 Phys. Rev. D 104, 032003 experiment. A conservative uncertainty of 7% was assumed for absolute counting rates. ●In KI model exclusion is even more strict. ●Exclusions based on absolute IBD rates for large ∆m2 support previous results (Daya Bay, Bugey-3, ...) Fission fraction reconstruction 7 years of running ●3 detector positions, pure positron kinetic energy (annihilation photons not included) ●> 8 mln IBD events, ~ 5000 events per day in the closest position ●Signal/Background > 50 ●Reactor power is measured by the DANSS with neutrino flux with 1.3% accuracy in 3 days during more than 7 years! Top position Middle position Bottom position ●Correction for dead time, efficiency, neighbor reactors power (individually) ●Mean normalization for the whole campaign is used ●Reactor #4 power and fission points distribution profile are not taken into account ●Fit range: 1-3 and 5.5-7 MeV (excluding so-called “bump”) ●Difference in 235U fraction between KNPP and DANSS is ~3% ●The estimated ratio of σ5 /σ9 = 1.54 ± 0.06 is consistent with the HM model and it is slightly larger than the KI and Daya Bay results ●Obtained accuracy in 235U fission fraction reconstruction is ~3% ●Observed to predicted ratio with absolute νe counting rates is 0.98±0.04 for HM model, and is 1.02±0.04 for KI model ●DANSS excludes a large and the most interesting fraction of sterile neutrino parameter space using only rat