Speaker
Description
The Ricochet experiment aims to measure Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) induced by reactor antineutrinos using an array of 18 42-gram cryogenic germanium calorimeters equipped with simultaneous phonon and ionisation readouts for nuclear/electronic recoil discrimination, operated at $\sim$15 mK at the Institut Laue-Langevin (ILL). Cosmic-ray muons can produce secondary neutrons via spallation reactions in the surrounding materials, generating nuclear recoils in the sub-keV region of interest that are indistinguishable from the CE$\nu$NS signal. To mitigate this cosmogenic background, the Ricochet collaboration has deployed an active outer muon veto system that consists of 34 plastic scintillator panels complemented by a cryogenic inner veto to maximize solid-angle coverage. This poster presents an overview of the muon veto system, covering its operating principle, calibration, and efficiency estimation. The outer muon veto system shows excellent stability in both calibration and detection efficiency over multiple reactor-on and reactor-off periods.
A systematic study of the muon rate modulation induced by atmospheric pressure variations is presented: a clear anticorrelation between the measured muon rate and atmospheric pressure is observed, and its impact on the stability of the cosmogenic background is discussed. The coincidence analysis between the muon veto and the bolometers is detailed, which enables the tagging and rejection of cosmogenic nuclear recoil backgrounds.