Superconducting Bolometers for the RICOCHET Experiment

The RICOCHET experiment, located at the Institut Laue Langevin (ILL) in Grenoble, France, is a coherent elastic neutrino-nucleus scattering (CEνNS) observatory that aims to detect low-energy reactor anti-neutrinos (< 10MeV) through nuclear recoils. This low-energy frontier presents itself as an opportunity to probe neutrino physics beyond the Standard Model as the coherent interaction amplifies the cross section, reducing the total exposure required to reach new sensitivity limits or discovery. RICOCHET has been commissioned at ILL and has been operating since early 2024 with an exanding array of Ge detectors (CryoCube) utilizing heat and ionization readouts. We focus on the development of the complementary detector array (Q-Array), which uses superconducting crystals (e.g. Al, and Sn) of around 30 ∼50 grams as the recoil target and Mn-doped Al transition-edge-sensors (TESs) for calorimetric readout. We present and discuss the latest R&D data and a model based on the Boltzmann Transport Equation for particle interactions and transport phenomena in bulk superconductors. Because electron recoil background rejection is essential to achieve sensitivity to sub-keVee CEνNS signals, we use the model to gather physical insights and investigate the potential to use pulse shape information to distinguish electron and nuclear recoils. The transport model aims to explain the critical features of the detected signal shape.