Development of a High Energy Gamma-Ray Spectrometer for Laser-Plasma Experiments*

There is an abundance of existing gamma-ray detectors, but for laser-plasma experiments where ultrashort high-energy gamma rays are produced, existing detectors lack the response time to measure the energy spectrum through single hit detection. An initial scintillator-based design for a new spectrometer was created to infer the spectrum from the shape of the electromagnetic shower in the detector as gamma rays pass through an array of CsI scintillating rods. However, noise in the system and poor distinction between the responses to high-energy photons in the 200-500 MeV range have limited the spectral retrieval of this design to forward fitting methods that require prior knowledge of the spectral shape. The goal of this project is to develop a spectrometer that is less sensitive to noise and can retrieve the full spectrum without requiring existing knowledge. To this end, we used FLUKA simulations and codes in MATLAB to investigate how different materials and geometries impact the susceptibility of the spectral reconstruction to noise. We have explored new scintillator geometries to improve the conditioning of the matrix response. The spectrometer design will be built and used for ZEUS experiments to provide a full picture of the energy distribution of gamma rays.