The first JSNS${}^2$ measurement of electron neutrino flux using ${}^{12}C({\nu }_e,e^{-}{)}^{12}{N}_{g\mathrm{.}s\mathrm{.}}$ reaction

JSNS${}^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment searching for sterile neutrinos through the observation of ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_e$ 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 ${}^{12}\mathrm{C}({\nu }_e,e^{-}{)}^{12}{\mathrm{N}}_{g\mathrm{.}s\mathrm{.}}$ reaction in JSNS${}^2$, yielding a flux of (6.7 $\pm$ 1.6 (stat.) $\pm$ 1.7 (syst.)) $\times$ 10${}^{-9}$ cm${}^{-2}$ proton${}^{-1}$ at the JSNS${}^2$ detector location, located at 24 meters distance from the mercury target. This flux measurement is consistent with predictions from simulations based on hadron models.