Neutrino astrophysics in the multi-messenger era

Since 2013, the detection of a diffuse flux of high-energy neutrinos (0.1-10 PeV), in excess with respect to the atmospheric one, has opened a new window to the Universe, revealing the existence of extremely energetic astrophysical neutrino sources. Within the context of standard acceleration scenarios, this measurement implies that the processes responsible for the production of these particles proceed all the way up to multi-PeV energies.

In addition, in 2017 the first extra-galactic source of high-energy neutrinos was announced, namely TXS 0506+056. This was identified into a blazar, known since 1983 through its radio emission, and recently observed in flaring activity of multi-GeV gamma rays by Magic and Fermi. The observation of a multi-TeV neutrino emission from this source has assessed the fundamental role of neutrinos in the context of multi-messenger studies, since the presence of neutrinos as part of the flux originated by the astrophysical source can probe the physics of accelerated hadrons, and possibly test physics beyond the Standard Model.

Since the neutrino fluxes from cosmic sources are expected to be faint, of the order of few particles per km3 per year, and given the small cross-section of neutrino interactions, a Neutrino Telescope requires a large instrumented volume. This can be achieved by using the Cherenkov light revelation technique in transparent media, sucha as sea-water or ice.

The IceCube experiment at the South Pole, in operation for more than a decade, has reached the km3 dimension, paving the way with its discoveries to the era of neutrino astrophysics. The future generation of Neutrino Telescopes will consist of three-dimensional arrays of photomultipliers, deployed deep into the water of the Mediterranean Sea (at about few kilometres depth): it will observe the Cherenkov light induced in water by the passage of an ultra-relativistic charged particle, namely the secondary product of neutrino interaction with the surrounding water.

A Rome group, let's refer to it as “astrophysical neutrino group,” has been promoting for more than two decades the construction of a multi-km3 Neutrino Telescope in the Mediterranean Sea: at the beginning by participating in the NESTOR Collaboration, then with the activities performed within the INFN-NEMO program for the measurements of the environmental properties of deep-sea Mediterranean sites. Recently the astrophysical neutrino group in Sapienza University of Rome is involved in the operation of the current major neutrino telescope in the Northern Hemisphere, ANTARES, as well as in the construction of the next-generation cubic-kilometre detector, KM3NeT.

The KM3NeT project will consist of two detectors, built with the same technology, dedicated to two different aspects of neutrino physics:

In particular, at present the group has expertise in several research areas, ranging from the analysis of data collected by the aforementioned experiments, to the temporal and charge calibration of the detectors, as well as to the design and validation tests of the electronics used in the apparatus. In the context of multi-messenger data analysis, the group has been mainly working in correlation studies among high-energy neutrinos and high-energy gamma rays from Gamma-Ray Bursts (GRBs), the most energetic explosions of the Universe. In addition, in the same context of multi-messenger studies, the group has been active in correlations among high-energy neutrinos and ultra-high-energy cosmic rays (UHECRs). Concerning astronomical studies, the group has performed searches for dark matter from neutrino annihilation in the Galactic Center.

The group consists of 4 senior scientists, namely 1 full professor, 2 technologists and 1 University researcher, plus 2 post docs, 1 PhD student and 1 Master student: