New Shower Maximum Trigger for Electrons and Photons at CDF
  For the 1994 Tevatron collider run, CDF has upgraded the electron and photon trigger hardware to make use of shower position and size information from the central shower maximum detector. For electrons, the upgrade has resulted in a 50\% reduction in backgrounds while retaining approximately 90\% of the signal. The new trigger also eliminates the background to photon triggers from single-phototube discharge. 
David Gerdes, the CDF Collaboration