1. 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

2. 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)

3. 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 to 12.7 m
The top position corresponds to ~15000 IBD events per day for 100% efficiency
Cosmic muon suppression measured
Igor Alekseev (ITEP)

4. 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)

5. 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)

6. 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)

7. 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)

8. 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 us
No muon triggers from -100 us
Igor Alekseev (ITEP)

9. 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)

10. 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)

11. The crew on board
Igor Alekseev (ITEP)

12. 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: [physics.ins-det]
The first data recorded in April 2016
Preliminary analysis show about 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
Igor Alekseev (ITEP)

13. Backups
Igor Alekseev (ITEP)

14. Time between μ–veto trigger and neutron candidateus
Time between μ–veto trigger and neutron candidate
Igor Alekseev (ITEP)

15. µ-events – signal events
Igor Alekseev (ITEP)

16. µ-events – signal events
Igor Alekseev (ITEP)

17. 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)