Neutral-current neutrino cross section and expected supernova signals for ${}^{40}$Ar from a three-fold increase in the magnetic dipole strength

In view of the great interest in liquid argon neutrino detectors, the ${}^{40}$Ar($\gamma ,{\gamma }^{\mathrm{\prime }}$)${}^{40}$Ar${}^{\ast }$ reaction was revisited to guide a calculation of the neutral current neutrino cross section at supernova energies. Using the nuclear resonance fluorescence technique with a monoenergetic, 99% linearly polarized photon beam, we report a three-fold increase in magnetic dipole strength at around 10 MeV in ${}^{40}$Ar. Based on shell-model calculations, and using the experimentally identified transitions, the neutral current neutrino cross sections for low-energy reactions on ${}^{40}$Ar are calculated.