DVCS Calorimeter Trigger System Requirements

	Sergey Boyarinov, Stepan Stepanyan
	October 2007

DVCS Calorimeter Trigger System Overview

	DVCS Calorimeter Trigger System must search for the clusters produced by photons or electrons; normally presence of at least two clusters will be required for calibration runs (search for two photons from pi0 decay) and at least one cluster for production runs (search for one electron)
	Cluster is defined as more then N towers (N<=9) with energy deposition above threshold located within 3x3 towers  rectangular area (figure on following slide)
	CAEN v895B discriminators and v1495 logic unit will be used
	Hodoscope will be installed in front of DVCS calorimeter, it must part of the trigger system as well

Slide 3

Trigger System requirements

	System takes 424 ECL signals from 27 CAEN v895 calorimeterÕs discriminators and process them on v1495 logic units
	System takes 60-80 (to be decided) ECL signals from 5 CAEN v895 hodoscopeÕs discriminators and process them on v1495 logic units
	System delivers 1 ECL signal to be used as CLAS Trigger Supervisor ASYNC input: level Ô1Õ means ÔpassÕ, level Ô0Õ means ÔfailÕ
	Trigger logic is controlled by following parameters: discriminators thresholds, the number of towers per cluster (from 1 to 9), the minimum number of clusters (one or two), overlap area between calorimeter cluster and hodoscope hit. Size of cluster search window is fixed and always 3x3 towers
	Following picture shows preliminary electronics layout

Slide 5

Time scale

	Preliminary design: October 2007
	Hardware orders: October 2007
	FPGA simulation completion: November 2007
	Hardware assembly and testing: February-March 2008
	System must be completely ready by June 2008