RICOCHET is an international collaboration aiming to explore the Coherent Elastic Neutrino-Nucleus Scattering (CeνNS), a long-predicted interaction that was observed experimentally only in 2017. Neutrinos have no electric charge, an extremely small mass, and interact only weakly with matter. They typically pass through normal matter undetected and are not easy to study. At low energy, neutrinos are expected to interact mainly through CEνNS, where a neutrino scatters off a nucleus (via Z-boson exchange) and the nucleus recoils as a whole. A precise measurement of the nuclear recoil spectrum for reactor neutrinos, where the process is fully coherent, could reveal deviations from the Standard Model of particle physics, potentially unlocking the door to new physics.

The installation of the RICOCHET experiment at the ILL was proposed within an open call for proposals in 2020. The preparation of the site started in 2022 and the installation of the experiment was completed in 2024. After one year of commissioning, the experiment began its initial science phase in July 2025. The instrument is located only 8.8 meters away from the core of ILL’s High Flux Reactor. This proximity provides an intense neutrino flux of approximately 10¹² neutrinos/cm²/s, ideal for studying CEνNS at low (sub-keV) recoil energies.

Instrument setup 

RICOCHET employs germanium-based cryogenic calorimeters, called the CryoCube technology, operated at 15 mK. When an antineutrino scatters off a nucleus in the crystal, the resulting nuclear recoil disturbs the crystal lattice, generating phonons, and ionizes the surrounding detector material. Each crystal is equipped with both a phonon sensor and aluminum electrodes. The simultaneous readout of phonon and ionization signals allows discrimination between nuclear recoils (caused by CEνNS but also by fast neutrons), electronic recoils (caused by gamma rays), and heat-only events (events that produce negligible ionization), which is essential for background suppression.

In its first scientific phase, RICOCHET operates 18 detectors of 42 grams each. The CryoConcept Hexa-Dry 200 dilution refrigerator is equipped with ultra quiet technology (UQT) to minimize noise induced by vibrations from the pulse tube. The cryostat is surrounded by a 22-ton external shield of borated polyethylene and lead to reduce reactogenic and radiogenic backgrounds. The instrument is placed below the reactor’s transfer channel providing about 15 metres water equivalent of overburden against cosmic radiation. An active muon veto detector around the shielding tags cosmic muons which can create fast neutrons in the lead.