Observation of low-lying isomeric states in ${}^{136}$Cs: a new avenue for dark matter and solar neutrino detection in xenon detectors

We report on new measurements establishing the existence of low-lying isomeric states in ${}^{136}$Cs using $\gamma$ rays produced in ${}^{136}$Xe(p,n)${}^{136}$Cs reactions. Two states with $\mathcal{O}(100)$~ns lifetimes are placed in the decay sequence of the ${}^{136}$Cs levels that are populated in charged-current interactions of solar neutrinos and fermionic dark matter with ${}^{136}$Xe. Xenon-based experiments can therefore exploit a delayed-coincidence tag of these interactions, greatly suppressing backgrounds to enable spectroscopic studies of solar neutrinos and dark matter.