New results from the DANSS experiment

TL;DR

The DANSS experiment analyzed millions of neutrino events over five years at various distances from a reactor, finding no significant evidence for sterile neutrinos but providing precise measurements of reactor neutrino flux and fission fractions.

Contribution

This study provides new constraints on sterile neutrino parameters and confirms the reactor neutrino flux predictions with high precision.

Findings

No significant evidence for sterile neutrinos (best-fit 1.3σ).

Excluded sterile neutrino mixing angles up to sin^2 2θ_ee < 0.008.

Measured reactor neutrino flux and fission fraction dependence consistent with models.

Abstract

The DANSS experiment collected 5.5 million Inverse Beta Decay (IBD) events during 5 years of operation. Data were collected at 3 distances (10.9~m, 11.9~m, and 12.9~m) from the center of the core of the industrial $3.1~GW$ reactor. The IBD event rate exceeds 5000/day at the smallest distance. The detector position was changed usually 3 times a week. Therefore in the analysis that uses information only about relative IBD counting rates and changes in positron energy spectra shapes many systematic uncertainties were canceled out. No statistically significant evidence for sterile neutrinos is found. The significance of the best-fit point in the 4$\nu$ case is only 1.3$\sigma$. The excluded area covers a very interesting range of the sterile neutrino parameters up to $sin^22\theta_{ee} < 0.008$ in the most sensitive region. The IBD rate dependence on the fission fraction of $^{239}$Pu was measured. It agrees with the predictions of the Huber-Mueller model. The reactor power was measured during more than 4 years with $\approx2\%$ accuracy in 2 days using the rate of neutrino events normalized to the thermal power at the initial period.