KM3NeT: First detection of an ultra-high-energy neutrino

Despite their abundance in the Universe, neutrinos interact very little with matter, making these ‘ghost particles’ difficult to detect. These cosmic messengers, with a mass a million times less than that of an electron, are emitted in a straight line during cosmic events. The study of neutrinos provides us with valuable information about the extreme astrophysical phenomena from which they originate, information that is otherwise inaccessible using more conventional methods.
An exceptional detection has just been made: that of a neutrino with an unprecedented energy of around 220 petaelectronvolts (PeV), thirty times greater than all the neutrinos previously detected on a global scale. The study of this event could provide unique clues about the processes at work in the most energetic sources in the Universe, or about the interaction of extreme-energy cosmic rays with the cosmic microwave background.

SUBATECH's KM3NeT group has been involved in this collaboration since 2017, and has made a major contribution to this analysis, in particular by calibrating the instrument and determining the direction of arrival of this neutrino. For several years, SUBATECH's researchers and technical team have been integrating optical modules, participating in their deployment at the French site, taking part in the development of the experiment's software and computing environments, contributing to calibration and data processing campaigns, and finally looking at their interpretation in a multi-messenger astronomy context.

© T. Gál, Collaboration KM3NeT.

The 21 detection lines made up of 18 optical modules (black spheres) and a buoy make up the detector at the time of observation. The Eiffel Tower is shown to indicate the scale. The red line symbolises the trajectory of the neutrino and the large blue cone represents the wake of the Cherenkov light. Each coloured sphere indicates an individual light recording associated with a photomultiplier. The size of the spheres is proportional to the intensity of the light signal detected, and the colour corresponds to the time shift of the Cherenkov light (blue, then yellow to purple).