Fast neutron background characterization of the future Ricochet experiment at the ILL research nuclear reactor

The future Ricochet experiment aims at searching for new physics in the electroweak sector by providing a high precision measurement of the Coherent Elastic Neutrino-Nucleus Scattering (CENNS) process down to the sub-100 eV nuclear recoil energy range. The experiment will deploy a kg-scale low-energy-threshold detector array combining Ge and Zn target crystals 8.8 meters away from the 58 MW research nuclear reactor core of the Institut Laue Langevin (ILL) in Grenoble, France. Currently, the Ricochet collaboration is characterizing the backgrounds at its future experimental site in order to optimize the experiment's shielding design. The most threatening background component, which cannot be actively rejected by particle identification, consists of keV-scale neutron-induced nuclear recoils. These initial fast neutrons are generated by the reactor core and surrounding experiments (reactogenics), and by the cosmic rays producing primary neutrons and muon-induced neutrons in the surrounding materials. In this paper, we present the Ricochet neutron background characterization using $^3$He proportional counters which exhibit a high sensitivity to thermal, epithermal and fast neutrons. We compare these measurements to the Ricochet Geant4 simulations to validate our reactogenic and cosmogenic neutron background estimations. Eventually, we present our estimated neutron background for the future Ricochet experiment and the resulting CENNS detection significance.Comment: 14 pages, 14 figures, 1 tabl

Optimization and performance of the CryoCube detector for the future RICOCHET low-energy neutrino experiment

International audienceThe RICOCHET reactor neutrino observatory is planned to be installed at Institut Laue-Langevin starting in mid-2022. The scientific goal of the RICOCHET collaboration is to perform a low-energy and percentage-precision CENNS measurement in order to explore exotic physics scenarios beyond the standard model. To that end, RICOCHET will host two cryogenic detector arrays : the CryoCube (Ge target) and the Q-ARRAY (Zn target), both with unprecedented sensitivity to O(10)eV nuclear recoils. The CryoCube will be composed of 27 Ge crystals of 38g instrumented with NTD-Ge thermal sensor as well as aluminum electrodes operated at 10mK in order to measure both the ionization and the heat energies arising from a particle interaction. To be a competitive CENNS detector, the CryoCube array is designed with the following specifications : a low energy threshold ($\sim 50$eV), the ability to identify and reject with a high efficiency the overwhelming electromagnetic backgrounds (gamma, betas, X-rays) and a sufficient payload ($\sim 1$kg). After a brief introduction of the future RICOCHET experiment and its CryoCube, the current works and first performance results on the optimization of the heat channel and the electrode designs will be presented. We conclude with a preliminary estimation of the CryoCube sensitivity to the CENNS signal within RICOCHET

HEMT-based 1K front-end electronics for the heat and ionization Ge CryoCube of the future RICOCHET CEν\nuNS experiment

International audienceThe RICOCHET reactor neutrino observatory is planned to be installed at the Laue Langevin Institute (ILL) starting mid-2022. Its scientific goal is to perform a low-energy and high precision measurement of the coherent elastic neutrino-nucleus scattering (CE$\nu$NS) spectrum in order to explore exotic physics scenarios. RICOCHET will host two cryogenic detector arrays: the CryoCube (Ge target) and the Q-ARRAY (Zn target), operated at 10 mK. The 1 kg Ge CryoCube will consist of 27 Ge crystals instrumented with NTD-Ge thermal sensors and charge collection electrodes for a simultaneous heat and ionization readout to reject the electromagnetic backgrounds (gamma, beta, x-rays). We present the status of its front-end electronics. The first stage of amplification is made of High Electron Mobility Transistor (HEMT) developed by CNRS/C2N laboratory, optimized to achieve ultra-low noise performance at 1K with a dissipation as low as 15 $\mu$W per channel. Our noise model predicts that 10 eV heat and 20 eVee RMS baseline resolutions are feasible with a high dynamic range for the deposited energy (up to 10 MeV) thanks to loop amplification schemes. Such resolutions are mandatory to have a high discrimination power between nuclear and electron recoils at the lowest energies

Fast neutron background characterization of the future Ricochet experiment at the ILL research nuclear reactor

The future Ricochet experiment aims at searching for new physics in the electroweak sector by providing a high precision measurement of the Coherent Elastic Neutrino-Nucleus Scattering (CENNS) process down to the sub-100 eV nuclear recoil energy range. The experiment will deploy a kg-scale low-energy-threshold detector array combining Ge and Zn target crystals 8.8 meters away from the 58 MW research nuclear reactor core of the Institut Laue Langevin (ILL) in Grenoble, France. Currently, the Ricochet collaboration is characterizing the backgrounds at its future experimental site in order to optimize the experiment's shielding design. The most threatening background component, which cannot be actively rejected by particle identification, consists of keV-scale neutron-induced nuclear recoils. These initial fast neutrons are generated by the reactor core and surrounding experiments (reactogenics), and by the cosmic rays producing primary neutrons and muon-induced neutrons in the surrounding materials. In this paper, we present the Ricochet neutron background characterization using $^3$He proportional counters which exhibit a high sensitivity to thermal, epithermal and fast neutrons. We compare these measurements to the Ricochet Geant4 simulations to validate our reactogenic and cosmogenic neutron background estimations. Eventually, we present our estimated neutron background for the future Ricochet experiment and the resulting CENNS detection significance