Superconducting Bolometers for the Ricochet Experiment

The Ricochet experiment at the Institut Laue–Langevin (ILL) in Grenoble, France, is a CEνNS observatory targeting low-energy reactor antineutrinos (<10MeV) via nuclear recoils. Exploiting the coherent enhancement of the cross section, Ricochet opens a low-energy sensitivity frontier that enables searches for physics beyond the Standard Model with modest exposure. Ricochet has been operating since early 2024 with an expanding Ge detector array (CryoCube) instrumented for simultaneous heat and ionization readout. We focus on the complementary Q-Array, which uses superconducting crystals (e.g., Al and Sn) of roughly 30g to 50g as recoil targets and Mn-doped Al transition-edge sensors (TESs) for calorimetric readout. We present recent R&D results and a transport model based on the Boltzmann transport equation that describes quasiparticle and phonon dynamics in bulk superconductors. Because robust rejection of electron-recoil backgrounds is essential for sensitivity to sub-keVee CEνNS signals, we use the model to investigate how prompt and delayed signal components can potentially differentiate electronic recoils from nuclear recoils.