Preprint WISC-EX-94-334

The ZEUS Calorimeter First Level Trigger

W.H. Smith, I. Ali, B. Behrens, C. Fordham, C. Foudas, A. Goussiou,
M. Jaworski, T. Kinnel, J. Lackey, P. Robl, S. Silverstein
University of Wisconsin, Madison, WI, USA,
J.W. Dawson, D.A. Krakauer, R.L. Talaga, J.L. Schlereth
Argonne National Laboratory, Argonne, IL, USA


Submitted to Nuclear Instruments and Methods

Abstract

The design of the ZEUS Calorimeter First Level Trigger (CFLT) is presented. The CFLT utilizes a pipelined architecture to provide trigger data for a global first level trigger decision 5 $\mu$sec after each beam crossing, occurring every 96 nsec. The charges from 13K phototubes are summed into 1792 trigger tower pulseheights which are digitized by flash ADC's. The digital values are linearized, stored and used for sums and pattern tests. Summary data is forwarded to the Global First Level Trigger for each crossing 2 $\mu$sec after the crossing occurred. The CFLT determines the total energy, the total transverse energy, the missing energy, and the energy and number of isolated electrons and muons. It also provides information on the electromagnetic and hadronic energy deposited in various regions of the calorimeter. The CFLT has kept the experimental trigger rate below $\approx$ 200 Hz at the highest luminosity experienced at HERA. Performance studies suggest that the CFLT will keep the trigger rate below 1 kHz against a rate of proton-beam gas interactions on the order of the 100 kHz expected at design luminosity.