Simulating the neutrino flux from the Spallation Neutron Source for the COHERENT experiment

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is a pulsed source of neutrons and, as a by-product of this operation, an intense source of pulsed neutrinos via stopped-pion decay. The COHERENT collaboration uses this source to investigate coherent elastic neutrino-nucleus scattering and other physics with a suite of detectors. This work includes a description of our geant4 simulation of neutrino production at the SNS and the flux calculation which informs the COHERENT studies. We estimate the uncertainty of this calculation at the $\ensuremath{\sim}10%$ level based on validation against available low-energy ${\ensuremath{\pi}}^{+}$ production data.