NUTRIG: novel techniques for pure, efficient and scalable autonomous radio detection of high energy neutrinos and cosmic rays

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The origin of ultra-high energy cosmic rays - the most energetic particles in the Universe, sometimes exceeding energies of 10^20 eV - is still a mystery, after more than a century of theoretical and experimental research. Detection of cosmic neutrinos beyond energies of 10^17 eV may allow to identify their source. These elusive messengers would be precious tools to study violent phenomena in the Universe, especially if their observation is combined with that of gravitational waves, gamma rays or electromagnetic waves at other wavelengths. One of the most promising and mature experiment proposals so far for the observation of these ultra-high energy neutrinos consists in deploying giant radio arrays covering areas of 100,000 km^2 or beyond, such as proposed by the GRAND project in particular. Such radio arrays would detect the targeted cosmic particles (neutrinos or cosmic rays) thanks to the transient radio emission of particle showers induced by their interaction in the atmosphere. The very affordable radio technique is perfectly adapted to achieve the gigantic detection areas needed to collect the rare particles observed at these extreme energies. Yet, a major unsolved challenge lies in the realization of an autonomous online rejection of background radio transients (associated with a wealth of sources such as power lines, radio communication on Earth, air planes, thunderstorms, etc.) which induce - even in remote, desertic areas such as the one targeted by GRAND - a much higher rate of radio pulses than air showers. We propose with the NUTRIG project to address this specific issue by developing an efficient and pure triggering system, scalable to giant areas, which will allow selecting radio transients associated with cosmic particles through specific signatures which differ from those of background signals. This unique project, developed by our German-French collaboration, will be validated in real conditions using the GP300 experiment, a pathfinder for the GRAND project. The combined expertise of our two teams, experts in the field of cosmic rays and autonomous radio detection of air showers, puts us in a perfect position to address this key issue, and will pave the way for future giant detectors of cosmic particles.