The experiment Neutrino-4 on the search for sterile neutrino at SM-3 reactor
1. The direct observation of sterile neutrino oscillation in Neutrino-4 experiment
2. Possibility of experimental confirmation of the 3 + 1 neutrino modelwith one sterile neutrino
A.P. Serebrov
NRC KI - Petersburg Nuclear Physics Institute, 188300 Gatchina, Russia

Neutrino-4 collaboration

1NRC “KI” Petersburg Nuclear Physics Institute, Gatchinа, Russia

2JSC “SSC Research Institute of Atomic Reactors”, Dimitrovgrad, Russia
3Dimitrovgrad Engineering and Technological Institute MEPhI, Dimitrovgrad, Russia

TWENTIETH LOMONOSOV CONFERENCE ON ELEMENTARY PARTICLE PHYSICS
Moscow State University, Moscow, 19-25 August, 2021

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The direct observation of effect of oscillation in Neutrino-4 experimenton search for sterile neutrino
A.P. Serebrov, et al. PHYSICAL REVIEW D 104, 032003 (2021)

The periodof oscillation
for neutrino energy
4 MeV is 1.4 m
A.P.Serebrov, et al.
JETP Letters,
Volume 109, 2019
Issue 4, pp 213–221.
JETP Letters,
Volume 112, 2020
Issue 4, pp 211–225.
arxiv:2003.03199
arXiv:2005.05301v 82

Reactor SM-3Week protection from cosmic
rays (3-5 m w. e.)

90 MW thermal power
Compact core 42x42x35cm
Highly enriched 235U fuelDue to some peculiar characteristics of its construction, reactor SM-3 provides the most favorable conditions tosearch for neutrino oscillations at short distances. However, SM-3 reactor, as well as other research reactors, islocated on the Earth’s surface, hence, cosmic background is the major difficulty in considered experiment.

3

Movable and spectrum sensitive antineutrino detector at SM-3 reactor

epeen1.
2.
3.
4.
5.
6.
7.
8.
9.

Neutrinochanneloutsideandinsidedetector (5x10 cells)
internal active shielding
external active shielding
steel and leadborated polyethylene
moveable platform
feed screw
step motor
shielding

GdDetector
prototype

Full-scaledetector

Passive shielding - 60 tons

Range of measurements is 6 – 12 meters

Liquid scintillator detector
50 sections 0.235x0.235x0.85м34

OFF  (7  1)%

cosmic background - OFF

ON-OFF antineutrino signal

ON-OFF  (9  2)%

The correlated signal produced by the cosmic backgroundmeasured over the whole time (up). The correlated ON-OFF
signal over the whole time (down).

The distribution of deviations fromaverage value of correlated events
rates background (OFF) anddifferences (ON-OFF) normalized on
their statistical uncertainties.

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Energy calibration of the full-scale detector
Pu-Be neutron source
22 Na- gamma source

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BACKGROUND SPECTRUM

Presence of that structure in the energy spectrum indicates that energy calibrationof the detector was the same in all measurements.
Еnergy resolution of the detector σ=250 keV which does not depend on the energy of a positron.

7Comparison of MC spectrum of antineutrino for 235U with the experimental ON-OFF spectrum

calculated MC spectrum of antineutrino for 235U

experimental ON-OFF spectrum.

difference normalized to the calculated
spectrum

Spectrally independent method foranalyzing experimental data is needed8N ( Ei , Lk )Number ofantineutrino
events

Probability of antineutrino disappearance
2 [eV2 ]L[m]mP(e  e )  1  sin 2 214 sin 2 (1.27 14)E [MeV](1)The spectrum independent method of experimental data analysis

Riexp,k 

N ( Ei , Lk ) L2k
1KK  N ( Ei , Lk )Lk2k

S ( E ) ( E )[1  sin 2 214 sin 2 (1.27 m124 Lk / Ei )]K2 L / E )]S ( E ) ( E ) K  [1sin 2 214 sin 2 (1.27 m14k i
1

 Rith,k(2)kThe denominator is significantly simplified with a range of measurement distances significantly greater than thecharacteristic oscillation period:𝑆(𝐸 ሻ - Spectrum ( E ) - Detector efficiency
exp
exp 2th 2222[(RR)/(R)]
(sin2,m i,k i,k14 )
14i ,ki,k9

2The results of the analysis of optimal parameters m14 and sin 2 2θ14 using 2 method

exp 2th 22R)
/(R)
]


(sin 214 , m )
[( Riexp,ki,ki ,k2

2
14i ,kWe observed theoscillation effect at
C.L. 2.9 in vicinity of :2m14 7.25eV 2Expected from
Neutrino-4
CL 99.7%

Excluded from
Neutrino-4
CL>99.9% CL

sin 2 2θ14  0.3610𝚫𝒎𝟐𝟏𝟒= 𝟕. 𝟑𝟎 ± 𝟎. 𝟏𝟑𝒔𝒕 ± 𝟏. 𝟏𝟔𝒔𝒚𝒔𝒕
𝒔𝒊𝒏𝟐 𝟐𝜽𝟏𝟒 = 𝟎. 𝟑𝟔 ± 𝟎. 𝟏𝟐
The periodof oscillation
for neutrino energy
4 MeV is 1.4 m

A.P. Serebrov, et al.
PHYSICAL REVIEW D104, 032003 (2021)

A.P.Serebrov, et al.
JETP Letters,
Volume 109, 2019
Issue 4, pp 213–221.
JETP Letters,
Volume 112, 2020
Issue 4, pp 211–225.
arxiv:2003.03199
arXiv:2005.05301v 811

A.P.Serebrov, et al. JETP Letters, Volume 109, 2019 Issue 4, pp 213–221

A.P. Serebrov, et al. PHYSICAL REVIEW D 104, 032003 (2021)

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There is a maximum at zero, from here theprocess of oscillations begins

It should be noted that theexperimental points should be
fitted with such a sinusoidal
dependence,whichhasamaximum at the origin, since theprocess of oscillations starts fromthe source. This significantly
reduces the set of sinusoids
available for fitting. FIG. shows
the complete curve of theoscillation process starting fromthe reactor.

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ANALYSIS OF POSSIBLE SYSTEMATIC EFFECTS
Reactor ON

Comparison of the R-ratio versus L/E for theneutrino signal (top)
Reactor OFF

and the R-ratio versus L/E for the
background (bottom).

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RESULT OF THE EXPERIMENT NEUTRINO-42Δ𝑚14= 7.30 ± 0.13𝑠𝑡 ± 1.16𝑠𝑦𝑠𝑡 = 7.30 ± 1.17.

𝑠𝑖𝑛2 2𝜃14 = 0.36 ± 0.12(2.9𝜎ሻMonte Carlo based statistical analysis gave an estimation of the confidence level at 2.7σ.

15Possibility of experimental confirmationof the 3 + 1 neutrino modelwith one sterile neutrino

16THE STRUCTURE OF 3+1 NEUTRINO MODEL AND REPRESENTATION OF
PROBABILITIES OF VARIOUS OSCILLATIONS

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The relations of oscillations parameters required for comparative analysis ofexperimental results are:

The first important conclusion of the 3 + 1 model is that the oscillation frequency in allprocesses should be the same, i.e. it is determined by the value
𝚫𝒎𝟐𝟏𝟒
The second important relation for experimental verification of the 3 + 1 model.

1 2sin 2   sin 214 sin 2 2 2442

This relationship can be interpreted in a fairly simple way. The appearance of electron
neutrinos in a muon neutrino beam: this is a second-order process, i.e. transition of amuon neutrino to a sterile neutrino, and then the transition of a sterile neutrino into anelectron neutrino.
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COMPARISON OF NEUTRINO-4 WITH ICECUBE, MINIBOONE AND LSND
A.P. Serebrov *, R.M. Samoilov JETP Letters, Volume 112, 2020 Issue 4, pp 211–225 arxiv:2003.03199

MINIBOONE AND LSNDICECUBE

NEUTRINO-4𝚫𝒎𝟐𝟏𝟒= 𝟕. 𝟑𝚫𝒎𝟐𝟏𝟒= 𝟕. 𝟑Neutrino-4 CL 95% +IceCube

0.36

0.1

0.009 without RAA
0.005

0.009

0.360.1

without RAA

0.005

0.19
with RAA

0.1

with RAA

Test of neutrino model 3+12Δm14= 4.47+3.53−2.08

sin2 2𝜃24 = 0.10+0.102−0.07

ICECUBE
19A.P. Serebrov , Lomonosov Conference. 17-40. 20.08.2021

COMPARISON OF NEUTRINO-4 MASS PREDICTION WITH MEASUREMENT OF NEUTRINO MASS
A.P. Serebrov *, R.M. Samoilov JETP Letters, Volume 112, 2020
Issue 4, pp 211–225 arxiv:2003.03199

𝒎𝟒 = (𝟐. 𝟕𝟎 ± 𝟎. 𝟐𝟐ሻ𝐞𝐕, 𝑚𝜈2 ሻ𝒎𝐞𝐟𝐟𝝂𝒆 = (𝟎. 𝟓𝟗 ± 𝟎. 𝟏𝟏ሻ𝐞𝐕

20A.P. Serebrov , Lomonosov Conference. 17-40. 20.08.2021

Neutrino flavors mixing scheme including sterile neutrino and effective mass hierarchy
A.P. Serebrov *, R.M. Samoilov JETP Letters, Volume 112, 2020 Issue 4, pp 211–225 arxiv:2003.03199

PMNS matrix for 3 + 1 model

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A.P. Serebrov , Lomonosov Conference. 17-40. 20.08.2021

Conclusion
1.The direct observation of sterile neutrino
oscillation in Neutrino-4 experiment

2. Possibility of experimental confirmation of the 3 + 1 neutrino model with one sterile neutrino

2Δ𝑚14= 7.30 ± 0.13𝑠𝑡 ± 1.16𝑠𝑦𝑠𝑡

sin2 2𝜃 = 0.36 ± 0.12𝑠𝑡𝑎𝑡 (2.9𝜎ሻ
3. COMPARISON OF NEUTRINO-4 MASS PREDICTION
WITH MEASUREMENT OF NEUTRINO MASS

4. Neutrino flavors mixing scheme includingsterile neutrino and effective mass hierarchy

5. PMNS matrix for 3 + 1 modelThus, the analysis performed provides quite interesting generalizations and an indication of the possibility of22the validity of the 3 + 1 neutrino model with one sterile neutrino.

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