First JSNS² measurement of the electron neutrino flux using the (Formula presented) reaction

JSNS² (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment searching for sterile neutrinos through the observation of (Formula presented) appearance oscillations, using neutrinos produced by muon decay-at-rest. A key aspect of the experiment involves accurately understanding the neutrino flux and the quantities of pions and muons, which are progenitors of (anti)neutrinos, given that their production rates have yet to be measured. We present the first electron-neutrino flux measurement using (Formula presented) reaction in JSNS², yielding a flux of ð6.7 ± 1.6ðstatÞ ± 1.7ðsystÞÞ × 10⁻⁹ cm⁻² proton⁻¹ at the JSNS² detector location, located at 24 meters distance from the mercury target. This flux measurement is consistent with predictions from simulations based on hadron models.