The polarization sensitivity of GRETINA*

Characterization of the spins and parities of nuclear states, including excited states, is fundamental to nuclear structure physics.  Direct measurement of these quantities can be achieved through Compton polarimetry, which exploits the sensitivity of the Compton-scattering cross section to the polarization state of incident photons.  Historically, such studies have been conducted with dedicated experimental setups using multiple detectors in specific geometries which offer high sensitivity, but very limited efficiency. In contrast, γ-ray tracking arrays, such as the Gamma Ray Energy Tracking In-beam Nuclear Array (GRETINA), provide sensitivity to the Compton scattering angles throughout their active volumes, thereby achieving both high polarization sensitivity and high γ-ray detection efficiency simultaneously.  Using the well-studied reaction ²⁴Mg(p,p'γ), which produces highly linearly-polarized γ rays, we have performed an experiment to characterize GRETINA as a Compton polarimeter.  The analysis of the data and resulting performance of the array will be discussed.