AA new neutrino detector is built within an international Chooz-2 project by Russian and French researchers. New detector will help observe antineutrino from nuclear reactors of the Chooz nuclear power plant, Ardennes, France. Studying fundamental properties of neutrino is important for particle physics, astrophysics and cosmology.

Neutrinos are electrically neutral elementary particles. Nature created three types of neutrino and three types of respective antiparticles. Existence of these particles was predicted in 1930, however, neutrinos were observed for the first time in 1956, because they very weakly interact with other particles, and any kind of matter is transparent for neutrinos.

In late 1990s scientists received important evidence that an effect of neutrino oscillations existed. These experiments received the Nobel Prize in Physics 2002. Oscillations describe how one neutrino type is transformed into another, and this phenomenon can happen only, when neutrinos have masses. Oscillations depend on three parameters – mixing angles, two of have already been measured and shown to be large. The third mixing angle 1-3 is extremely small and hasn’t been measured to date. Researchers know only its upper limit. New Chooz detector is the first representative of a new generation of reactor experiments, aimed at measuring mentioned third fundamental parameter of neutrino physics, a key field of studying elementary particles. Results of this experiment will have important consequences for development of new neutrino experiments, aimed at new precision measurements.

 

 

The Chooz-2 project provides building two identical detectors. First detector, located 1 kilometer away from nuclear reactors and filled with a scintillation fluid, has already started data acquisition. In 2011 researchers expect to significantly improve detector sensitivity for the 1-3 parameter. Second detector is located 400 meters away from the reactors and is expected to start operation in 2012. 400 meters is the distance, at which the effect of neutrino oscillations cannot be detected yet. Comparison of data, coming from both detectors, can result in highly accurate measurement of 1-3 mixing angle.

Each detector contains organic scintillation fluid, which was specially designed for this very experiment. Neutrino target, located in the centre of the detector, consists of 10 cubic meters of a scintillation fluid with added gadolinium, which allows registering positrons and neutrons, coming from inverse beta decay, caused by reactor neutrino. The target is surrounded by three layers of other fluid for protection from space particles and suppression of radioactivity. The target is observed by 390 submerged photomultipliers, which transform signals of neutrino interactions into electric pulses. These pulses are accumulated and processes in an electronic measuring facility, ready for operation within following 5 years. Activation of new reactors is a guarantee that neutrino physics remains one of most productive fields of particle physics.

Chooz-2 collaboration unites research and development institutions from England, Brazil, Germany, Spain, Russia, United States of America, France and Japan.