Experiment Neutrino-4 on search for sterile neutrino А. Serebrov Collaboration Neutrino-4: 1. NRC “KI” Petersburg Nuclear Physics Institute, Gatchinа, NRC 2. “Kurchatov institute”, Moscow, 3. JSC “SSC RIAR”, Dimitrovgrad, Russia 4. DETI MEPhI, Dimitrovgrad, 433511 Russia А Serebrov1, V Ivochkin1, R Samoilov1, А Fomin1, A Polyushkin1, V Zinoviev1, P Neustroev1,V Golovtsov1, А Chernyj1, О Zherebtsov1, V Martemyanov2, V Tarasenkov2, V Aleshin2, А Petelin3, А Izhutov3, А Тuzov3, S Sazontov3, D Ryazanov4, М Gromov3, V Afanasiev3, М Zaytsev1, 4, М Chaikovskii1 Международная сессия-конференция Секции ядерной физики ОФН РАН "Физика фундаментальных взаимодействий", посвященная 50-летию Баксанской нейтринной обсерватории 6-8 июня 2017 г.
The reactor antineutrino anomaly and sterile neutrino G. Mention et al., Phys. Rev. D83, 073006, 2011 The reactor antineutrino anomaly and sterile neutrino
Experiment Neutrino-4 at SM-3 reactor 1 Petersburg Nuclear Physics Institute NRC KI, Gatchinа, 2 NRC “Kurchatov institute”, Moscow, 3 JSC “SSC RIAR”, Dimitrovgrad, 4 DETI MEPhI, Dimitrovgrad, SM-3 WWER-1000 100 MW 60 MW 85 MW 20 MW 250 MW Size of active zone of reactor SM-3: 424235 cm 2700 MW 3000 MW Core size and power of different reactors
Prototype of NEUTRINO-4 detector, 400 l The model of the neutrino detector installed in passive shielding 1 – detector of reactor antineutrino, 2 – passive shielding, 3 – rail, 4 – the engine for detector movement, 5 – active shielding with PMT, 6 – volume with liquid scintillator liquid with Gd (~ 400 l), 7 – Detector PMT.
Assembling of electronics for prototype of NEUTRINO-4 detector
Computer room – data processing We begin the first measurements on model of the neutrino detector
Outlay of the neutrino laboratory (left side - passive shielding of neutrino detector, 60 tons)
General view of neutrino laboratory
First version of active shielding Second version of active shielding External active shielding – "umbrella"
The problem of fast neutrons Neutron scattering imitate neutrino reaction
Multi-section model of detector liquid scintillator PTM Table 1. The probability of double-start events registration in various sections. central section side section corner section average 0.42 0.29 0.19 0.30 Monte-Carlo calculations
Multi-section antineutrino detector model The detector consists of 16 sections 22.5 x 22.5 x 50 cm3 with fixed baffles. The baffles are made of acrylic plastic and have specular surface serve to prevent light from leaving the section. Scintillator material is mineral oil (CH2) with addition of Gadolinium 1g per litter.
General scheme of installation . 1 – detector of reactor antineutrino, 2 – internal active shielding, 3 – external active shielding (umbrella), 4 – steel and lead passive shielding, 5 – borated polyethylene passive shielding, 6 – moveable platform, 7 – feed screw, 8 – step motor.
The full-scale detector with liquid scintillator volume of 3 m3 (5x10 sections) is installed already
Comparison with calculation Share of multi starts Comparison with calculation calculation central cell, double coincidence side cell, angular cell, in all cells, 0.424 0.294 0.188 0.372 OFF Experiment ON-OFF 0.37 ON
Results of measurement of antineutrino flux from distance, and spectra
Example of data set in month. 178 useful (ON – OFF) events in days. Relation effect/background (ON-OFF)/OFF = 0.57
Results of measurements of antineutrino flux from distance Goodness of fit (1/L2) Goodness of fit (1/L^2) 12% L
Results of measurements of antineutrino flux from distance Goodness of fit (1/L^2) 16% L
ν counting rate dependence on distance from reactor core D А N S Detector was split into 3 sections along z (~30cm each) Each section has 3 positions – up, middle, down Normalization (efficiency) for central section is a fit parameter Difference in efficiencies of central and 2 other sections are also fit parameters DANSS Preliminary Const/R2 Data are provided M. V. Danilov Perfect agreement with 1/R2 dependence
Results of measurements of antineutrino flux from distance Neutrino-4 + DANSS
Results of measurements of antineutrino flux from distance Neutrino-4 + DANSS
Results of measurements of antineutrino flux from distance Neutrino-4 + DANSS
GoF = 81%.
The reactor antineutrino anomaly and sterile neutrino G. Mention et al., Phys. Rev. D83, 073006, 2011 The reactor antineutrino anomaly and sterile neutrino
averaged spectrum on all distances Goodness of fit 13% (Average distance 8.6 m)
Spectral ratio of experimental prompt signals to expected signals without oscillation for average spectrum (Average distance 8.6 m) Goodness of fit 13%
Calculated spectral ratio and experimental spectral ratio Goodness of fit 78%
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plot from spectral analysis of Neutrino-4 data 95%
plot from analysis of distance dependence 95%
Joint analysis (distance + spectrum)
Conclusions by results of the current measurements Dependence of flux of antineutrino is measured for the first time at small distances (6 – 12 m to the reactor center) by means moveable detector. 2. Within the available statistical accuracy reliable deviations from the law 1/L^2 where L – distance to the center of the reactor aren't revealed. The deviation at the level 90% CL isn't significant yet to consider it as reliable deviation. 3. The carried-out analysis within model of a sterile neutrino show a possibility of existence of a sterile neutrino with parameters: However the deviation at the level 90% CL isn't significant yet to declare about observation of sterile neutrino. Analysis of a possible systematics is required also.
Future plans is the preparation of new neutrino laboratory at SM-3 reactor in room №170 with two moveable detectors
Plans: 1. Continuation of measurements on this installation in room №162. 2. Creation of the second neutrino laboratory on the SM-3 reactor with base up to 15 meters in room №170. 3. Two identical detectors, one - stationary on 15 m, the second - mobile. 4. Detectors with PMT from two sides, on 25 PMT from each side. Only 100 PMT. 5. Discrimination of a signal on a form of an impulse (PSD). 6. New scintillator with 0.3%Gd, for suppression of a background of accidental coincidence. ( 3 cubic meters).
Neutrino laboratory on the SM-3 reactor in room №170 (The aim is the increasing of the accuracy of measurements with factor of 2 or 3) 15 m - 5 m SM-3 reactor 1 Scheme of two detectors AS AS (active shielding) AS 2 Fe 10 cm CH2B 50 cm PMT 9354 (25X2)
Best regards from Dimitrovgrad А Serebrov1, V Ivochkin1, R Samoilov1, А Fomin1, A Polyushkin1, V Zinoviev1, P Neustroev1,V Golovtsov1, А Chernyj1, О Zherebtsov1, V Martemyanov2, V Tarasenkov2, V Aleshin2, А Petelin3, А Izhutov3, А Тuzov3, S Sazontov3, D Ryazanov4, М Gromov3, V Afanasiev3, М Zaytsev1, 4, М Chaikovskii1 1 Petersburg Nuclear Physics Institute NRC KI, Gatchinа, 188300 Russia 2 NRC “Kurchatov institute”, Moscow, 123182 Russia 3 JSC “SSC RIAR”, Dimitrovgrad, 433510 Russia 4 DETI MEPhI, Dimitrovgrad, 433511 Russia
Studies of background condition by means of gamma and neutron detectors Gamma detector NaJ Thermal neutron detector He3 PuBe (n) Neutron source Fast neutron detector Calibration procedure
Fast neutrons are the most danger Measurement of fast neutron flux near the reactor wall (outside the shielding) during increase reactor power flux of fast neutron 10-3s-1cm-2 Fast neutrons are the most danger
Distribution of fast neutrons fluxes inside shielding at Р=90 MWt and at 0 MWt flux of fast neutron 9 x10-5s-1cm-2
Fast neutrons flux (s-1cm-2) Thermal and fast neutrons fluxes inside shielding and on top of shielding, Р=90 MWt. Thermal neutrons flux (s-1cm-2) Fast neutrons flux (s-1cm-2) Place of measurment (0.34±0.07) 10-5 (4.4±0.5) 10-5 Inside (17.7±1.2) 10-5 (69±2) 10-5 On the top Shielding factor Кth= 53 Shielding factor Кfast = 16
near the reactor wall inside the shielding 137Cs 60Co
Gamma-rays background distribution inside shielding, Reactor on (Gamma detector NaJ)
Spectral-integrated dependence Neutrino-4 NEOS DANSS Biological reactor shielding
Spectral-integrated dependence for nuclear power plant NEOS DANSS
Neutrino-4 7 m DANSS 11.7 m NEOS 24 m
Background of accidental coincidence. Spectral dependence. Different distances and power of the reactor. 7.11 метра 10.87 метра
Background of accidental coincidence, spectral dependence.
NEOS
Neutrino-4
Neutrino-4 7 m DANSS 11.7 m NEOS 24 m prompt energy prompt energy
Neutrino-4 7 m DANSS 11.7 m NEOS 24 m
500 m
Different part of spectrum at the different distance R/A background Neutrons Muons Soft component of cosmic rays
Detector active shielding For multi-section detector
The detector is based on reaction of the inverse β -decay
Signal of correlated events time of arrival of the second impulse prompt signal delayed signal 10 s 100 s time window
Cosmic rays background
The effects of atmospheric temperature and pressure on cosmic rays 5% 8% 14%
Time spectra for different configurations of active shielding (AS) No AS, Muons 1.54 c-1 = 2,2 = 30 No AS, Neutrons 0.15 c-1 Neutrons 0.011 c-1
The problem of fast neutrons Neutron scattering imitate neutrino reaction
Multi-section model of detector liquid scintillator PTM Table 1. The probability of double-start events registration in various sections. central section side section corner section average 0.42 0.29 0.19 0.30 Monte-Carlo calculations
Multi-section antineutrino detector model The detector consists of 16 sections 22.5 x 22.5 x 50 cm3 with fixed baffles. The baffles are made of acrylic plastic and have specular surface serve to prevent light from leaving the section. Scintillator material is mineral oil (CH2) with addition of Gadolinium 1g per litter.
General scheme of installation . 1 – detector of reactor antineutrino, 2 – internal active shielding, 3 – external active shielding (umbrella), 4 – steel and lead passive shielding, 5 – borated polyethylene passive shielding, 6 – moveable platform, 7 – feed screw, 8 – step motor.
The full-scale detector with liquid scintillator volume of 3 m3 (5x10 sections) is installed already
Fig. 5. Results of energy calibration.
Distribution of signals on sections from capture of a neutron gadolinium Monte Carlo Experiment а – result of Monte Carlo of modeling (the neutron is taken in the middle of section), b– the result received on the sectioned detector (in relative units).
Distribution of an event of capture of a neutron gadolinium by quantity of the involved sections. Distribution of the detained signals concerning a cell (3, 3) in which there was a reaction of the inverse beta decay.
Improvement of the relation a signal/background due to sectioning S/B =0.1 S/B =0.1 S/B =0.3 S/B =0.3 sectioning S/B =0.6
Spectra of prompt signals for different distances
GoF = 48%.
Spectral ratio of experimental prompt signals to expected without oscillation for average spectrum Calculated spectral ratio of prompt signals to expected signals without oscillation for different