A Calorimeter-Based Level-One Electromagnetic Cluster Trigger for LHC

Level-one triggering at LHC will be very challenging. We have studied the problem of recognition of electromagnetic clusters and have developed an algorithm based on the transverse energy distribution in an electromagnetic calorimeter. This receives 8-bit digitised energies from a 4 x 4 window in the calorimeter. Two cluster thresholds and two isolation thesholds are provided, all of which are programmable. The algorithm has been been implemented as a gate array in 0.8 µm CMOS technology, and is performed using pipelined processing at 67 MHz. The gate array has been tested at full speed, and is being incorporated into a small prototype trigger processor to be tested with beam in conjunction with prototype calorimeters.