S. Miscetti

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 ! en and Z ! ee decays, we measure the energy threshold for a time to be recorded to be 3:8 � 0:3 GeV ð1:9 � 0:1 GeVÞ in the central (plug) portion of the detector. Similarly, for the central (plug) portion we measure a timing resolution of 600 � 10 ps ð610 � 10 psÞ 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. r 2006 Published by Elsevier B.V. PACS: 07.50.Qx; 29.40.Vj; 29.40.Mc

Properties of photon plus two-jet events in {ovr p}p collisions at {radical}{ovr s}= 1.8 TeV.

We present the first general measurements (invariant-mass, transverse-energy, and angular distributions) of the process, {bar p}p{r_arrow}{gamma}+2 jets+X, using data collected by the CDF at Fermilab. We compare the data with predictions from a tree-level QCD calculation and the PYTHIA shower Monte Carlo program. Our data sample is particularly sensitive to contributions from initial- and final-state radiation of photons and jets. Using the PYTHIA Monte Carlo program, we contrast the kinematical distributions for direct photon production with those for initial- and final-state photon radiation (bremsstrahlung). Based on the angular distributions, we find that our data favor a mixture of bremsstrahlung and direct photon production, as predicted, over either process alone. {copyright} {ital 1997} {ital The American Physical Society}