The 2nd international conference on particle physics and astrophysics 10-14 October 2016, Milan Hotel, Moscow, Russia Detector of the reactor AntiNeutrino based on Solid-state plastic Scintillator (DANSS). Status and first results. Igor Alekseev* for the DANSS collaboration: ITEP(Moscow) + JINR(Dubna) *ITEP, MEPhI, MIPT

The aim of the experiment is in registration of the reactor antineutrino in the reaction of Inverse Beta-Decay (IBD) Fast (prompt) signal Ee = Eν – 1806 MeV Delayed signal Physics goal: sterile neutrino search in the short range region Engineering goals: power monitoring, fuel composition, actual reaction center position Igor Alekseev (ITEP)

KNPP - Kalinin Nuclear Power Plant, Russia WWER1000 reactor KNPP - Kalinin Nuclear Power Plant, Russia Below 3.1 GW commercial reactor DANSS on a lifting platform No flammable or dangerous materials – can be put just after reactor shielding Reactor fuel and body provide overburden ~50 m w.e. for cosmic background suppression Lifting system allows to change the distance between the centers of the detector and of the reactor core from 10.7 to 12.7 m The top position corresponds to ~15000 IBD events per day for 100% efficiency Cosmic muon suppression measured Igor Alekseev (ITEP)

Scintillation strips 10x40x100 mm3 with Gd- dopped coating Polystyrene based scintillator WLS fibers to PMT SiPM Grooves with fibers Gd containing coating 1.6 mg/cm2 10 layers = 20 cm X-Module 1 layer = 5 strips = 20 cm Y-Module PMT 100 fibers Scintillation strips 10x40x100 mm3 with Gd- dopped coating Double PMT (groups of 50) and SiPM (individual) readout Strips along X and Y – 3D-picture 2500 strips = 1 m3 of sensitive volume Multilayer closed passive shielding: electrolytic copper frame ~5 cm, borated polyethylene 8 cm, lead 5 cm, borated polyethylene 8 cm 2-layer active μ-veto on 5 sides Igor Alekseev (ITEP)

Specially designed DAQ system PAs HVDAC WFD Input amplifiers ADCs FPGAs Power and VME buffers Clean room Preamplifiers PA in groups of 15 and SiPM power supplies HVDAC for each group inside shielding, current and temperature sensing STP cables to get through the shielding Total 46 Waveform Digitisers WFD in 4 VME crates on the platform WFD: 64 channels, 125 MHz, 12 bit dynamic range, signal sum, trigger generation and distribution (no additional hardware) 2 dedicated WFDs for PMTs and μ-veto System trigger on certain energy deposit in the whole detector (PMT based) or μ-veto signal Each channel selftrigger on SiPM noise (with decimation) Igor Alekseev (ITEP)

Single pixel SiPM signal Selftrigger PMT signal ~27 MeV System trigger ADCu Single pixel SiPM signal Selftrigger ADCu PMT signal ~27 MeV System trigger Exceptionally low electronic noise High dynamic range t, ns t, ns ADCu 1 pixel 2 pixels 4 pixels 3 pix. SiPM signal ~4.5 MeV System trigger SiPM noise spectrum t, ns Igor Alekseev (ITEP)

Energy spectrum of the neutron detection Example of a muon track in the detector body Calibration channels for source insertion into the detector body Gd(n,γ) H(n,γ) Energy spectrum of the neutron detection Igor Alekseev (ITEP)

Trigger = digital sum of PMT > 0.5 MeV IBD event = two time separated triggers: Positron track and annihilation Neutron capture by gadolinium Trigger rate ~ 1 kHz. IBD rate ~ 0.1 Hz.  Suppression factor >105 required. Main idea of the analysis: two triggers within 50 us: Backgrounds: SiPM noise – distort energy distribution – suppressed by ±15 ns time window Accidental correlation – imitate IBD event, but can be exactly subtracted Fast neutrons from cosmic muons – full imitation of IBD events  we need muon veto Neutron >3 MeV Multiplicity >=4 Better signature Positron >1 MeV Continuous ionization cluster events 50 us window No triggers from -50 us to + 100 us No muon triggers from -100 us Igor Alekseev (ITEP)

Mathematically strict procedure Before subtraction Accidental background After subtraction Accidental background: look for “positron” event in 50 us intervals 5, 10, 15 etc ms before neutron candidate. Do 16 intervals to minimize statistical error. Cuts for the accidental coincidence exactly the same as for physics events Mathematically strict procedure All physics distributions = events - accidental events/16 Igor Alekseev (ITEP)

Positron spectrum Top (7 days exposure) Middle (15 days) µ-BG Top (7 days exposure) Middle (15 days) Bottom (5 days) Positron spectrum µ-BG subtructed Pure positron kinetic energy (annihilation photons not included) About 5200 neutrino events/day in detector fiducial volume of 78% Pessimistic muon background estimate 5% based on 95% μ–veto geometrical coverage Igor Alekseev (ITEP)

The crew on board Igor Alekseev (ITEP)

arXiv:1606.02896 [physics.ins-det] Detector with a cubic meter of plastic scintillator in ~11 m from the core of 3.1 GW industrial reactor constructed. arXiv:1606.02896 [physics.ins-det] The first data recorded in April 2016 Preliminary analysis show about 5 200 antineutrino events per day with less than 5% cosmic background Data taking continues after two month of shutdown for upgrades in summer μ-veto improved for better geometrical coverage More interesting results follow soon The work is partially supported by the State Corporation «RosAtom» through the state contract Н.4х.44.9Б.16.1006 Igor Alekseev (ITEP)

Backups Igor Alekseev (ITEP)

Time between μ–veto trigger and neutron candidate us Time between μ–veto trigger and neutron candidate Igor Alekseev (ITEP)

µ-events – signal events Igor Alekseev (ITEP)

µ-events – signal events Igor Alekseev (ITEP)

Oscillation parameters: Dm2≈2 eV2 Sin2(2q)≈0.17 Ratios of the positron cluster energy measured at different detector position (dashed lines Z correspond to no oscillation case) Igor Alekseev (ITEP)