Radio-detection of neutrinos

GRAND will be array of 200,000 antennas over 200,000 square kilometers in mountainous and radio-quiet regions to collect 100s of neutrinos with ultra-high energy and angular resolution of a fraction of degree. Several hotspots of ~10,000 square kilometers will be deployed on several continents.

Detection Principle

Earth-skimming cosmic ντs can produce τ particles underground through charged-current interaction. τs travel to the surface of the Earth and decay in the atmosphere, generating extensive air showers (EAS). Coherent electromagnetic radiation is associated to the shower development at frequencies of a few to hundreds of MHz at a detectable level for showers with E > 1017 eV. The strong beaming of the electromagnetic emission combined with the transparency of the atmosphere to radio waves allows the radio-detection of EAS initiated by τ decays at distances up to several tens of kilometers. Inclined showers can leave footprints of several kilometers on the ground after traveling such large distances in the atmosphere, allowing a sparse antenna distribution.

Why Radio?

● A mature and autonomous technique rivaling with standard techniques, as demonstrated by AERA, LOFAR, Tunka-Rex, and TREND.
● Well-adapted for the detection of inclined showers, as induced by neutrinos: radio waves are not attenuated in the atmosphere, leading to 100-km² radio footprints on the ground, tens of kilometers away from the shower source.
● Radio antennas are cheap and robust: ideal for the deployment of giant arrays.

Preferred sites

GRAND antennas are foreseen to operate in the 30‑200 MHz frequency band. Short wave background prevents detection below this range, and above the coherence of the geomagnetic emission fades. Remote sites, with low electromagnetic background, should obviously be considered for the array location. In addition, mountain ranges are preferred, first because they offer an additional target for the neutrinos, and also because mountain slopes are better suited to the detection of horizontal showers compared to flat areas, parallel to the showers trajectories.