The timing system for the CDF electromagnetic calorimeters

We report on the design and performance of the electromagnetic calorimeter timing readout system (EMTiming) for the Collider Detector at Fermilab (CDF). The system will be used in searches for rare events with high-energy photons to verify that the photon is in time with the event collision, to reject cosmic-ray and beam-halo backgrounds, and to allow direct searches for new, heavy, long-lived neutral particles that decay to photons. The installation and commissioning of all 862 channels were completed in Fall 2004 as part of an upgrade to the Run II version of the detector. Using in situ data, including electrons from W→eνW→eν and Z→eeZ→ee decays, we measure the energy threshold for a time to be recorded to be 3.8±0.3GeV(1.9±0.1GeV) in the central (plug) portion of the detector. Similarly, for the central (plug) portion we measure a timing resolution of 600±10ps(610±10ps) for electrons above 10 GeV (6 GeV). There are very few system pathologies such as recording a time when no energy is deposited, or recording a second, fake time for a single energy deposit.