1. 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, 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.

2. The reactor antineutrino anomaly and sterile neutrino
G. Mention et al., Phys. Rev. D83, , 2011
The reactor antineutrino anomaly and sterile neutrino

3. 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: 424235 cm
2700 MW
3000 MW
Core size and power of different reactors

6. 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.

7. Assembling of electronics for prototype of NEUTRINO-4 detector

8. Computer room – data processing
We begin the first measurements on model of the neutrino detector

9. Outlay of the neutrino laboratory
(left side - passive shielding of neutrino detector, 60 tons)

10. General view of neutrino laboratory

11. First version of active shielding
Second version of active shielding
External active shielding – "umbrella"

12. The problem of fast neutrons
Neutron scattering imitate neutrino reaction

13. 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

14. 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.

15. 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.

16. The full-scale detector with liquid scintillator volume of
3 m3 (5x10 sections) is installed already

17. 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

18. Results of measurement of antineutrino flux from distance, and spectra

19. Example of data set in month.
178 useful (ON – OFF) events in days.
Relation effect/background (ON-OFF)/OFF = 0.57

20. Results of measurements of antineutrino flux from distance
Goodness of fit (1/L2)
Goodness of fit (1/L^2) 12% L

21. Results of measurements of antineutrino flux from distance
Goodness of fit (1/L^2) 16% L

22. 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

23. Results of measurements of antineutrino flux from distance
Neutrino-4 + DANSS

24. Results of measurements of antineutrino flux from distance
Neutrino-4 + DANSS

25. Results of measurements of antineutrino flux from distance
Neutrino-4 + DANSS

26. GoF = 81%.

27. The reactor antineutrino anomaly and sterile neutrino
G. Mention et al., Phys. Rev. D83, , 2011
The reactor antineutrino anomaly and sterile neutrino

28. averaged spectrum on all distances
Goodness of fit 13%
(Average distance 8.6 m)

29. Spectral ratio of experimental prompt signals to expected signals without oscillation
for average spectrum
(Average distance 8.6 m)
Goodness of fit 13%

30. Calculated spectral ratio and experimental spectral ratio
Goodness of fit 78%

31. ? !

32. plot from spectral analysis of Neutrino-4 data
95%

33. plot from analysis of distance dependence
95%

34. Joint analysis (distance + spectrum)

35. 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.

36. Future plans is the preparation
of new neutrino laboratory
at SM-3 reactor in room №170
with two moveable detectors

37. 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).

38. 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 m
SM-3 reactor 1
Scheme of two detectors AS
AS (active shielding) AS 2
Fe 10 cm
CH2B cm
PMT 9354 (25X2)

39. 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, Russia
2 NRC “Kurchatov institute”, Moscow, Russia
3 JSC “SSC RIAR”, Dimitrovgrad, Russia
4 DETI MEPhI, Dimitrovgrad, Russia

41. 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

42. 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

43. Distribution of fast neutrons fluxes inside shielding
at Р=90 MWt and at 0 MWt
flux of fast neutron 9 x10-5s-1cm-2

44. 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

45. near the reactor wall
inside the shielding
137Cs
60Co

46. Gamma-rays background distribution inside shielding,
Reactor on (Gamma detector NaJ)

47. Spectral-integrated dependence
Neutrino-4
NEOS
DANSS
Biological reactor shielding

48. Spectral-integrated dependence
for nuclear power plant
NEOS
DANSS

49. Neutrino-4
7 m
DANSS
11.7 m
NEOS
24 m

50. Background of accidental coincidence. Spectral dependence.
Different distances and power of the reactor.
7.11 метра
10.87 метра

51. Background of accidental coincidence, spectral dependence.

54. NEOS

56. Neutrino-4

60. Neutrino-4 7 m DANSS 11.7 m NEOS 24 m prompt energy prompt energy

61. Neutrino-4
7 m
DANSS
11.7 m
NEOS
24 m

62. 500 m

65. Different part of spectrum at the different distance
R/A background
Neutrons
Muons
Soft component of cosmic rays

66. Detector active shielding
For multi-section detector

67. The detector is based on reaction of the inverse β -decay

68. Signal of correlated events
time of arrival of the second
impulse
prompt signal
delayed signal
10 s
100 s
time window

69. Cosmic rays background

70. The effects of atmospheric temperature and pressure on cosmic rays5% 8%
14%

71. 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

72. The problem of fast neutrons
Neutron scattering imitate neutrino reaction

73. 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

74. 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.

75. 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.

76. The full-scale detector with liquid scintillator volume of
3 m3 (5x10 sections) is installed already

77. Fig. 5. Results of energy calibration.

78. 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).

79. 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.

80. 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

81. Spectra of prompt signals for different distances

82. GoF = 48%.

83. 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