Thesis (Ph.D.) - Indiana University, Department of Physics, 2020Coherent 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. The measured CEvNS cross section of (2.3$\pm$0.7) x 10$^{39}$cm$^2$, averaged over the incident neutrino flux, is consistent with the Standard Model prediction. This result represents a detection of CEvNS on the lightest nuclei so far and improves bounds on beyond-the-standard-model physics in the form of non-standard neutrino interactions.