The world’s biggest neutrino physics experiment using liquid scintillator
INFN’s research and technology have marked a new goal, carried on in particular by the Padua Division and the Department of Physics and Astronomy of Padua University.
On June 24th in fact the international collaboration JUNO (Jiangmen Underground Neutrino Observatory), that sees also the participation of INFN, has reached an important step on the way to an underground experiment for neutrino detection in southern China: the steel structure that will support the internal acrylic sphere, with a diameter of 35.4 m, has been completed. The internal sphere will contain all the instrumentation and materials that will allow the observation of these extremely elusive particles.
The group composed by researchers of INFN Padua and the Department of Physics and Astronomy of Padua University has created a crucial part of this equipment: the readout electronics of the more than 20000 large photomultipliers, that will serve as the “eyes” of the detector and will thus allow to reconstruct the energy released by the interaction of neutrinos in the liquid scintillator.
In fact, scintillator is a material that emits light pulses when the particles passing through it release energy. There are different kinds of scintillators with a variety of properties, determined by the material they are composed of. The experiment JUNO uses a liquid scintillator called alkyl-benzene (LAB).
“Despite the delays due to the pandemic, our Chinese colleagues have managed to respect the timetable established for the construction of JUNO” says Alberto Garfagnini, head of the Padua research group “it’s a very important result that opens the way to the next steps that will start in autumn, when the photomultipliers and the electronics designed by the Padua group will be installed”.
The particularity of the activity of the Padua group is that the detector readout electronics, unlike the case of the other running experiments worldwide, will be installed only a few metres away from the photomultipliers, submerged in the liquid scintillator. This will help in reducing the background electronic noise in the recorded signals, to increase the sensitivity of the detector itself, but has required some very strict building commitments that will not allow to repair or to replace any component after the installation, and for the entire 6 years of the duration of the experiment.
This is the reason why in May 2021 a very accurate test was carried on in order to confirm the efficiency and the impermeability of the electronic components, in collaboration with the Y-40 facility at Montegrotto Terme (PD): one of the deepest water pools in the world. This occasion provided the researchers with very similar conditions to the detector where the electronics will operate.
Jiangmen Underground Neutrino Observatory (JUNO) is an international collaboration, composed by more than 600 researchers from all over the world, for the design, building, and operation of the biggest underground liquid scintillator detector (20K tons) for neutrino physics. Besides Padua, INFN takes part in the JUNO collaboration with other Divisions and Laboratories: Ferrara, Catania, Milano, Milano Bicocca, Perugia, Roma 3 and National Laboratories of Frascati (LNF).
The JUNO Experiment will measure the energy of artificial antineutrinos produced by two large nuclear power plants, located at a distance of 53 km, to study the neutrino oscillations, the phenomenon that describes why these elusive particles, existing as three different types in nature, convert from one type to another.
In particular, JUNO will investigate the mass hierarchy, that is the order of the masses of the three known neutrino types. The experiment will also observe a variety of neutrinos of natural origin, from solar, atmospheric and terrestrial to supernova neutrinos, creating an in-depth and articulated research line in astroparticle physics.
Alberto Garfagnini, head of the Padua JUNO research group