Neutrino oscillation at very short distance
The neutrino is the most abundant massive particle in the universe but it is also the one that interacts the least. Because of this, and despite enormous experimental progress, it is one of the most enigmatic ingredients of the standard model of particle physics. Its nature and fundamental properties remain unknown: Dirac/Majorana, CP violation, absolute mass scale, other flavors… Recently, three independent experimental anomalies (Gallium, LSND/MiniBoone, reactor anomaly) support the hypothesis of the existence of a new neutrino family, called sterile because it does not interact by weak interaction. In this context, the SoLiD project (Search for Oscillation with Lithium-6 Detector) proposes to develop a new neutrino detection technology, allowing a robust measurement of the neutrino flux at very short distance from a nuclear reactor. It will then propose to disprove or confirm the reactor anomaly and to test in fine the hypothesis of this fourth sterile flavor.
The LPC has been involved since 2013 in the SoLiD project, which is now led by 10 international laboratories (France, Belgium, UK and USA). The objective is to deploy at the BR2 research reactor (SCK-CEN, Mol), a fiducial mass of about 2.9 t for oscillation distances between 5.5 and 12 m. To do this, the device must have a very high background rejection power. The proposed technology is based on two strong points: segmentation and the ability to “tag” the neutron signal. The detector consists of a 3D array of about 23000 PVT cubes (5cm3) read by an optical fiber network coupled to MPPCs. Each detection element contains a layer of Li6:Zns allowing to discriminate very cleanly the neutron signal from the background noise (figure 1). This technology combined with the particularly low background environment at BR2 allows the experiment to obtain an unprecedented sensitivity with a signal to noise ratio close to 6.