Pathfinder for a high statistics search for missing energy in gamma cascades

We investigate the feasibility of a high statistics experiment to search for invisible decay modes in nuclear gamma cascades using 200 kg of Cs(Tl) scintillators that are presently available at Texas A&M. The experiment aims to search for missing energy by robustly establishing the absence of a photon in a well-identified gamma cascade. We report on the experimental demonstration of the energy resolution necessary for this search. Prior explorations of this detector concept focused on baryonically coupled physics that could be emitted in E-2 transitions. We point out that this protocol can also search for particles that are coupled to photons by searching for the conversion of a photon produced in a gamma cascade into a hidden particle. Examples of these processes include the oscillation of a photon into a hidden photon and the conversion of a photon into an axionlike particle either in the presence of a magnetic field or via the Primakoff process. This proof of concept apparatus appears to have the ability to search for hitherto unconstrained baryonically coupled scalars and pseudoscalars produced in E-0 and M-0 transitions. If successfully implemented, this experiment serves as a pathfinder for a larger detector with greater containment that can thoroughly probe the existence of new particles with mass below 4 MeV that lie in the poorly constrained supernova "trapping window" that exists between 100 keV and 30 MeV.