BCAL Costhe Efficiency
Description of Method
We use the isotropy of the decay of pi0->gamma gamma to determine relative photon detection efficiencies. PI0 mesons are spineless particles and, therefore, their decay is isotropic in their rest frame. In addition, the photons are massless, so the energy distribution of the photons in the lab is directly related to the angular distribution in the pi0 rest frame. This fact allows us to infer relative inefficiencies in the photon detection efficiency from non-uniformities of the energy distribution in the lab. A description of the method and the results of the using this method for the 2017 data can be found in GlueX-doc-4002.