We report the first measurement of coherent elastic neutrino-nucleus scattering (CEvNS) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer CEvNS over the background-only null hypothesis with greater than $3\sigma$ significance. The measured cross section, averaged over the incident neutrino flux, is $(2.2\pm 0.7)\times {10}^{-39}{\mathrm{cm}}^2$—consistent with the standard model prediction. The neutron-number dependence of this result, together with that from our previous measurement on CsI, confirms the existence of the CEvNS process and provides improved constraints on nonstandard neutrino interactions.

• Received 3 April 2020
• Revised 28 September 2020
• Accepted 4 December 2020

DOI:https://doi.org/10.1103/PhysRevLett.126.012002