Periodic Reporting for period 1 - ESSCEvNS (Beyond the Standard Model: Coherent Neutrino Scattering at the European Spallation Source)
Reporting period: 2022-10-01 to 2025-03-31
Coherent Elastic Neutrino-Nucleus Scattering (CEvNS) is a recently demonstrated mechanism of neutrino interaction providing numerous new ways to study the properties of these elusive particles, as well as those of target nuclei. CEvNS also allows for a dramatic reduction in neutrino detector mass, enabling the construction of compact devices apt for a nonintrusive deployment at nuclear reactors and spallation facilities, both intense neutrino sources. This project aims to develop next-generation CEvNS detector technologies capable of studying this process at upcoming facilities such as the European Spallation Source (ESS), without the uncertainties associated to scarce signal statistics, i.e. by being able to acquire thousands of CEvNS interactions per year. Simultaneously we plan to improve the present understanding of detector response to the low-energy nuclear recoils produced by CEvNS, via dedicated calibration measurements. This knowledge is necessary to maximize the sensitivity of CEvNS experiments to still-unexplored neutrino characteristics (e.g. electromagnetic properties, non-standard interactions with quarks, etc.). The main concentration of this work is in the further development of p-type point contact (PPC) germanium detectors sensitive to sub-keV energy depositions, and in the construction of a large array of cryogenic undoped cesium iodide scintillators read out by innovative light sensors, developed in collaboration with European industry.
An improved PPC is presently operating 20 meters away from the core of the Vandellòs nuclear reactor, in its underground tendon gallery. This site provides an (anti)neutrino flux of 1.3E+13 neutrinos per square cm per second. This location will be used to test further advancements to this technology prior to a deployment at a suitable spallation source. We are well-advanced in the design of the CsI scintillator array, which will be instrumented using innovative light sensors (cryogenic large-area avalanche photodiodes -LAAPDs- with an elevated quantum efficiency of > 80%). These devices are not commercially available at the present time, and are being developed in collaboration with European industry (FAGOR Electrónica).
The combination of a very high light yield from cryogenic undoped CsI and optimal quantum efficiency of our LAAPDs will lead to an excellent response to ultra-low energy (sub-keV) nuclear recoils from CEvNS, improving our sensitivity to several neutrino properties. We have recently demonstrated a first detection of sub-keV recoils in an inorganic scintillator using this approach. However, their combination also holds promise in areas distant from fundamental particle physics, such as the development of low-cost PET medical imaging equipment with an improved resolution in energy and in spatial reconstruction. Separately, we have developed and tested an innovative design of portable neutron scatter camera. Its main purpose is the study of neutron backgrounds capable of affecting CEvNS experiments at spallation sources. An improved trigger design leads to a fully-isotropic response of the device to incoming neutron directions, as opposed to the conventional front-and-back sensitivity characteristic of these neutron imaging devices. This is expected to improve the performance of such devices in the area of Homeland Security, by reducing the exposure time necessary to identify concealed fissile materials.