RICOCHET is an international collaboration led by the CNRS and hosted at the ILL in Grenoble. It aims to exploit the Coherent Elastic Neutrino-Nucleus Scattering (CEνNS), a long-predicted interaction that was observed experimentally only in 2017. Its precise measurement could reveal deviations from the Standard Model of particle physics, potentially unlocking the door to new physics.

Neutrinos have no electric charge, an extremely small mass, and interact only weakly with matter. They typically pass through normal matter undetected and are 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.

The RICOCHET experiment was first proposed in 2017. It began its initial science phase in July 2025, after more than a year of commissioning, 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, ideal for studying CEνNS at low (sub-keV) recoil energies.

Instrument setup 

RICOCHET employs germanium-based cryogenic detectors, the CryoCube technology, cooled to 10 millikelvin. These detectors use a dual phonon-ionization readout, enabling them to distinguish CEvNS interactions from overwhelming environmental backgrounds. When an antineutrino scatters off a nucleus in the crystal, the subsequent nuclear recoil disturbs the crystal lattice, generating phonons that propagate through the detector, and ionizes the surrounding material, additionaly creating electron-hole pairs. Each crystal is equipped with both a phonon sensor and aluminum electrodes. This setup enables the simultaneous readout of the heat and ionization energies deposited in the crystal following any particle interaction.

The dual readout of heat and ionization energies is a key technological feature of the Ricochet experiment. It uniquely enables the identification of each recoiling particle, down to the sub-keV recoil energy range, thus providing highly efficient background suppression which is critical for an accurate CEνNS measurement.

With 18 detectors, each weighing about 42 grams, the experiment exposes a total germanium target mass of 750 grams to a neutrino flux of approximately 10¹² neutrinos/cm²/s. At an energy threshold of 50 eV_nr, the expected event rate is around 10 events per day. The Ricochet detectors are operated in a CryoConcept Hexa-Dry 200 dilution refrigerator 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 to limit reactogenic and radiogenic backgrounds.