Q-Array Deployment and Science Analysis for the Ricochet Experiment

Northwestern University, Evanston IL

Investigators

Abstract

Neutrinos, the “ghost” particles of fundamental physics, are the only know particle that clearly shows deviations from the predictions the standard model of particle physics. The Ricochet experiment will probe neutrinos using a new interaction which was only discovered in 2017 and provides a new way to study neutrino properties and possibly understand why neutrinos deviate from standard model predictions. Neutrinos might hold the key to understanding new physics beyond our current models; finding and understanding these new physics is a top question in nuclear and particle physics today and would lay the groundwork for a completely new revolution in nuclear, particle, and quantum physics. Ricochet will place an array of 36 detectors operating at a temperature just above absolute zero and eight meters from the core of a nuclear reactor in Grenoble, France. Nuclear reactors are the world’s strongest neutrino sources and placing these low-energy-threshold detectors so close to the reactor core will allow detection of tens of neutrino events per day, enabling the most accurate neutrino spectrum measurement to date. This project serves as a training ground for future scientists, as most of this work is done by graduate students and postdocs who not only design and fabricate the detectors but put together and operate the experiment and analyze and publish the results. This work has the following objectives: (1) design, build, install, commission, and operate nine of the detectors for Ricochet Phase 1 at the ILL nuclear reactor, (2) perform the analysis of the Ricochet data from all 36 crystals to produce the highest precision Coherent Elastic Neutrino-Nucleus Scattering (CEvNS) spectrum measurement to date and search for new physics, (3) continue Northwestern’s synergistic R&D program to use our Transition-Edge Sensor (TES) detectors for future CEvNS and neutrinoless double-beta decay (0nbb) experiments, and (4) train a new generation of neutrino experimental physicists. The Q-array is a 9-detector instrument that will demonstrate superconducting targets for reactor CEvNS measurements, provide target complementarity to the Ge-based CryoCube (the two of which form the payload of Ricochet phase 1), and lay the groundwork for implementing SQUID multiplexing for future neutrino cryogenic experiments with thousands of TES channels. Northwestern will participate in the full analysis of the Ricochet experiment, combining the 27 Ge detectors from the CryoCube and the nine Zn detectors from the Q-array to obtain world-leading sensitivity to the CEvNS process, making a percent-level measurement of the spectrum, and searching for new physics through Non-Standard Interaction modifications to the spectrum. Northwestern will optimize the TES modular architecture for future CEvNS and 0nbb experiments that will require excellent resolution, fast response, and thousands of channels. This will include demonstration of the TES technology on Lithium-Molybdate crystals in a prototype TES-based detector for CUPID 1-TON, and also demonstrate a TES-based Ge Ricochet Phase 2 detector with ionization readout. These activities will provide fertile ground for training of postdoctoral researchers, graduate students, and undergraduates, while sharing the excitement of science with the broader public. Finally, this work has a broad impact that extends beyond neutrino physics. Besides neutrino physics, the detectors being developed will also have applications in nuclear reactor monitoring applications, dark matter, and other low-threshold, high-energy resolution applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.