SoLid: Search for Oscillations with Lithium-6 Detector at the SCK-CEN BR2 reactor

G Ban,F Yermia,C Moortgat,J.M Buhour,M Labare,S Fresneau,G Guilloux,E Koonen,P Van Mulders,N Van Remortel,G Pronost,X Janssen,D Ryckbosch,M Fallot,B Coupé,Silva Kalcheva ,Dominique Durand ,A Cucoanes ,N C Ryder ,L Raes ,W Worby Beaumont ,J D’hondt ,Yu Shitov ,A Weber,L Giot,B Guillon,A Vacheret

doi:10.1016/j.nuclphysbps.2015.10.032

Abstract

Sterile neutrinos have been considered as a possible explanation for the recent reactor and Gallium anomalies arising from reanalysis of reactor flux and calibration data of previous neutrino experiments. A way to test this hypothesis is to look for distortions of the anti-neutrino energy caused by oscillation from active to sterile neutrino at close stand-off (∼6–8m) of a compact reactor core. Due to the low rate of anti-neutrino interactions the main challenge in such measurement is to control the high level of gamma rays and neutron background.The SoLid experiment is a proposal to search for active-to-sterile anti-neutrino oscillation at very short baseline of the SCK•CEN BR2 research reactor.This experiment uses a novel approach to detect anti-neutrino with a highly segmented detector based on Lithium-6. With the combination of high granularity, high neutron-gamma discrimination using 6LiF:ZnS(Ag) and precise localization of the Inverse Beta Decay products, a better experimental sensitivity can be achieved compared to other state-of-the-art technology. This compact system requires minimum passive shielding allowing for very close stand off to the reactor. The experimental set up of the SoLid experiment and the BR2 reactor will be presented. The new principle of neutrino detection and the detector design with expected performance will be described. The expected sensitivity to new oscillations of the SoLid detector as well as the first measurements made with the 8 kg prototype detector deployed at the BR2 reactor in 2013–2014 will be reported.

Highlights

The SoLid experiment is a proposal to search for active-to-sterile anti-neutrino oscillation at very short baseline of the SCKCEN BR2 research reactor
A few anomalies at a similar L/E have emerged in oscillation data at 2-3σ level: The LSND and MiniBooNE appearance results [1,2], the so-called “reactor anomaly” [3] after a recent re-evaluation of anti-neutrino spectra [4,5] and the Gallium anomaly from re-analysis of SAGE and Gallex calibration runs [6]
An oscillation into a sterile neutrino at short distance could explain these rate deficits consistently. This situation calls for new experimental data, in order to cross-check previous short baseline results with better control of the systematic uncertainties and test sterile neutrino hypothesis

Summary

Physics case

In the last few decades a vast number of experimental results established that neutrino oscillation occurs between three neutrino flavours and is a result of quantum effects arising from the tiny difference in their mass. The last two anomalies (electron neutrinos) disfavour the nooscillation hypothesis at 99.97% (3.6σ). It means, an oscillation into a sterile neutrino at short distance could explain these rate deficits consistently (if the sterile neutrino has a mass of ~1 eV). An oscillation into a sterile neutrino at short distance could explain these rate deficits consistently (if the sterile neutrino has a mass of ~1 eV) This situation calls for new experimental data, in order to cross-check previous short baseline results with better control of the systematic uncertainties and test sterile neutrino hypothesis. The sensitivity to small oscillations can be maximized by the use of a compact source (research reactor) coupled to a highly segmented detector with good energy reconstruction

The SCK-CEN BR2 research reactor

The SoLid experiment

Findings

Current status