The particle and nuclear astrophysics program addresses questions of fundamental physics in astrophysical systems. Current research topics include Solar Neutrinos, Neutrino Oscillations, WIMP Dark Matter searches, Neutrino-less Double Beta Decay, and detection of Ultra-High Energy Cosmic Rays.
Solar Neutrinos: Milano has a major role in the Borexino Solar Neutrino Experiment at the Gran Sasso Laboratory. The detector consists of 1300 tons of ultra-pure liquid scintillator, and it made the first direct-counting measurement of low-energy neutrinos from the Sun (7Be and pep neutrinos). The measurement has allowed to verify some fundamental features of neutrinos oscillations. It serves also as a fundamental test for the theory of the complex physics of the Sun and of stellar evolution.
Neutrino Oscillations: The Borexino detector is perfectly suited to host a short baseline neutrino oscillation experiment able to shed light on the several intriguing experimental hints accumulated so far pointing to the possible existence of a sterile neutrino at the few eV mass scale. The experiment will be carried out by using a 51Cr neutrino source placed close to the detector and in a second phase by deploying a 144Ce-144Pr anti-neutrino source inside the detector. The search for sterile neutrinos is also addressed by the Icarus collaboration, that is preparing a dedicated experiment with two liquid argon detectors complemented by magnetic spectrometers to be operated on a new short base line facility at CERN. Meanwhile, the analysis of data collected with the CNGS neutrino beam will provide results on neutrino interactions and neutrino oscillations. There are still many questions to be answered about neutrinos, questions that can point to new phyisics beyond the standard model. Some of these questions, like sterile neutrinos, the mass hierarchy and the existence of a CP-violating phases, can be aswered by accelerator neutrino beams coupled with massive Liquid Argon detectors, of which Icarus is the first successful prototype. Icarus is a pioneering detector, that can open the way to future experiments on proton decay and CP violation in the neutrino sector.
WIMP Dark Matter Searches: There is an overwhelming evidence that some 30% of the universe is in the form of cold dark matter, but the nature of this matter remains a mystery. The most attractive theory is that it is Weakly Interacting Massive Particles (WIMPs) that froze out of the early universe. A powerful way of detecting WIMPs directly in the local galactic halo is to look for the nuclear recoils produced when they collide with ordinary matter in a sensitive detector. DarkSide is an innovative experiment for the direct detection of dark-matter particles at Gran Sasso Laboratory. The design concept involves a two-phase, liquid-argon time-projection chamber (LAr-TPC) in which the energy released in WIMP-induced nuclear recoils can produce both scintillation and ionization.
Ultra High Energy Cosmic rays: The Pierre Auger Observatory (PAO) is an international cosmic ray observatory designed to detect ultra high energy cosmic rays. These are sub-atomic particles (protons or other nuclei) with energies beyond 10^20 eV. These high energy particles have an estimated arrival rate of 1 per square kilometer per century, therefore, in order to record a large number of these events, the Auger Observatory has created a detection area the size of 3000 square km The PAO is the largest ultra-high energy cosmic ray detector in the world and it is located on the vast plain of Pampa Amarilla in Argentina. The PAO is the first experiment that combines both ground and fluorescence detectors at the same site thus allowing cross-calibration and reduction of systematic effects that may be peculiar to each technique.