# IV international conference on particle physics and astrophysics

22-26 October 2018
Hotel Intourist Kolomenskoye 4*
Europe/Moscow timezone

## The first observation of effect of oscillation in Neutrino-4 experiment on search for sterile neutrino

23 Oct 2018, 16:45
25m
Petrovskiy hall (Hotel Intourist Kolomenskoye 4*)

### Petrovskiy hall

#### Hotel Intourist Kolomenskoye 4*

Kashyrskoye shosse, 39B, Moscow, Russia, 115409
Plenary/section talk Particle physics: neutrino physics

### Speaker

Prof. Anatolii Serebrov

### Description

We report Neutrino-4 experiment results of measurements of reactor antineutrinos flux and spectrum dependence on the distance in range 6-12 meters from the center of the reactor core. The fit of experimental dependence with the law $1⁄L^2$, where L is the distance from the reactor center, gave satisfactory result with goodness of fit 81%. However, we discovered that the experimental neutrino spectrum is different from the calculated one. Using experimental spectrum we performed the model independent analysis of restrictions on oscillation parameters $\Delta m_{14}^2$ and $sin^2 2\Theta_{14}$. The results of this analysis exclude area of reactor and gallium anomaly at C.L more than 99.7%
($>3\sigma$) for values $\Delta m_{14}^2 \le 4~eV^2$ and $sin^2 2\Theta_{14} > 0.1$. However, we observed an oscillation effect at C.L. 99.7% ($3\sigma$) in vicinity of $\Delta m_{14}^2 \approx 7~eV^2$ and $sin^2 2\Theta_{14} \approx 0.35$. The method of coherent addition of results of measurements, which allows us to directly observe the effect of oscillations, is proposed. The analysis of that effect is presented. In general, it seems that the effect predicted in gallium and reactor experiments is confirmed but at sufficiently large value of $\Delta m_{14}^2$. Future prospects of the experiment are discussed.

### Presentation Materials

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