The COHERENT collaboration's primary objective is to measure coherent elastic neutrino- nucleus scattering (CEvNS) using the unique, high-quality source of tens-of-MeV neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). In spite of its large cross section, the CEvNS process has never been observed, due to tiny energies of the resulting nuclear recoils which are out of reach for standard neutrino detectors. The measurement of CEvNS has now become feasible, thanks to the development of ultra-sensitive technology for rare decay and weakly-interacting massive particle (dark matter) searches. The CEvNS cross section is cleanly predicted in the standard model; hence its measurement provides a standard model test. It is relevant for supernova physics and supernova-neutrino detection, and enables validation of dark-matter detector background and detector-response models. In the long term, precision measurement of CEvNS will address questions of nuclear structure. COHERENT will deploy multiple detector technologies in a phased approach: a 14-kg CsI[Na] scintillating crystal, 15 kg of p-type point-contact germanium detectors, and 100 kg of liquid xenon in a two-phase time projection chamber. Following an extensive background measurement campaign, a location in the SNS basement has proven to be neutron-quiet and suitable for deployment of the COHERENT detector suite. The simultaneous deployment of the three COHERENT detector subsystems will test the N=2 dependence of the cross section and ensure an unambiguous discovery of CEvNS. This document describes concisely the COHERENT physics motivations, sensitivity and plans for measurements at the SNS to be accomplished on a four-year timescale.

This thesis describes the experimental work that finally led to a successful measurement of coherent elastic neutrino-nucleus scattering—a process proposed forty-three years ago. The experiment was performed at the Spallation Neutron Source facility, sited at Oak Ridge National Laboratory, in Tennessee. Of all known particles, neutrinos distinguish themselves for being the hardest to detect, typically requiring large multi-ton devices for the job. The process measured here involves the difficult detection of very weak signals arising from nuclear recoils (tiny neutrino-induced “kicks” to atomic nuclei), but leads to a much larger probability of neutrino interaction when compared to all other known mechanisms. As a result of this, “neutrino technologies” using miniaturized detectors (the author's was handheld and weighed only 14 kg) become a possibility. A large community of researchers plans to continue studying this process, facilitating an exploration of fundamental neutrino properties that is presently beyond the sensitivity of other methods.

This thesis highlights the development and analysis of multiple neutrino detectors deployed to the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory as part of the COHERENT experiment. It includes a preliminary measurement of the neutrino-induced neutron cross section on lead, and analysis that led to the first inclusive electron-neutrino charged-current measurement on iodine. These results add to the small number of inelastic neutrino-nucleus cross sections measured in this energy range, which are useful for understanding supernova and solar neutrino detection sensitivity. Additionally, it discusses preliminary work for and design of COHERENT’s ton-scale NaI coherent elastic neutrino-nucleus scattering (CEvNS) detector, currently being deployed to the SNS. Finally, it includes information on a campaign to measure the nuclear recoil quenching factor of NaI using multiple crystals, attempting to resolve inconsistencies with existing measurements.

Coherent elastic neutrino-nucleus scattering (CEvNS) was first proposed in 1974 but eluded detection for 40 years. The COHERENT collaboration made the first observation of CEvNS at the Oak Ridge National Laboratory Spallation Neutron Source (SNS) with a 14.6 kg CsI[Na] detector. One of the physics goals of the COHERENT experiment is to test the square of the neutron number dependence of the CEvNS cross section predicted in the Standard Model by observing CEvNS in multiple nuclei. To that end, the ~24 kg CENNS-10 liquid argon detector was deployed at the low-background Neutrino Alley at the SNS in early 2017. The detector was upgraded to allow for sensitivity to CEvNS in mid-2017. We analyzed 1.5 years of data taken after this upgrade to provide the first detection of CEvNS on an argon nucleus at >3 sigma significance.