Speaker
Description
The Ricochet experiment aims to detect Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) from antineutrinos produced at the Institut Laue-Langevin where it was deployed at the end of 2023, 8.8 meters away from the reactor core. The current CE$\nu$NS payload is an array of eighteen 42 g germanium cryogenic calorimeters, operated at 17 mK in a cryostat. To mitigate and reject external backgrounds, both passive shielding, composed of polyethylene and lead, and an active muon veto are installed around and inside the cryostat. Each detector is equipped with a dual phonon-ionization readout enabling the discrimination between nuclear recoils events -- which include the CE$\nu$NS signal -- and electronic recoils, constituting a background.
However, elastic scattering of fast neutrons, either ambient or due to cosmic rays interacting in the experimental setup, produces low-energy nuclear recoils in the detectors which cannot be rejected with particle discrimination. This background component is identical in every respect to the CE$\nu$NS signal, except that, unlike neutrinos, neutrons might scatter several times in the experimental volume. The poster presents a future upgrade option of the Ricochet experiment to reduce the remaining neutron background. The addition of a low-threshold cryogenic veto (repurposing eight 800 g germanium detectors from the EDELWEISS-III experiment) would allow us to tag multi-scattering neutron events. The design of the veto has been optimized, and its background rejection capabilities have been studied with GEANT4 simulations. Beyond the anticoincidence, these additional detectors could be used to improve the nuclear recoil calibration at low energy and to characterize the remaining backgrounds.