Calorimeter Timing System at CDF

We report on the design and performance of the electromagnetic calorimeter timing readout system (EMTiming) for the Collider Detector at Fermilab (CDF). The system is used in searches for rare events with high‐energy photons to verify that the photon is in time with the event collision, and to reject cosmic‐ray and beam‐halo backgrounds. The installation and commissioning of all 862 channels was completed in Fall 2004 as part of an upgrade to the Run II version of the detector. Using in‐situ data, we measure the energy threshold for a time to be recorded to be 3.8±0.3 GeV and 1.9±0.1 GeV in the central (CEM) and plug (PEM) portions of the detector. Similarly, for the central and plug portions we measure a timing resolution of 600±10 ps and 610±10 ps for electrons above 10 GeV (6 GeV). Pathologies such as noise and non‐Gaussian tails are virtually non‐existent.