Trigger Operation for Beam Run

Table: Summary of sub-detector triggers to GDL.

Detector		Label	# Bits	Comments
CDC	r$\phi$		2	CDC Full Track (N = 1, 2, 3)
			3	CDC Short Track (N = 1, 2, .. 7)
		CDC:B-B	1	CDC Back-to-Back Tracks
		CDC:open	1
	Z		2	CDC Z-track (N = 1, 2, 3)
TSC		TSC:Timing	1	TSC Timing Trigger ( 2)
			2	# of TSC hits (N=1,2,3)
		TSC:multi	1	(=2)
		TSC:patt	1	TSC pattern (1-3 back-to-back)
ECL			3
			4	Number of Isolated clusters (0-7,8)
		ECL:	1	ECL Bhabha (prescaled)
		ECL:	1	ECL Bhabha (non-prescale)
		ECL:Cosmic	1	ECL Cosmic
		ECL:Timing	1	ECL Timing (cluster 1)
KLM		MU	3	Hits in KLM Fwd,Barl,Bwd
EFC		EFC:BB	1	EFC Bhabha
		EFC:Tag	1	Tag for two-photon
CALIB		Random	1	Random trigger
		Revolution	1	Revolution signal
Total			32	+14 spare (= 48)

Table  summarizes the sub-triggers fed into GDL. The final triggers are categorized as follows:

1. Multi-track triggers: These require three or more tracks in CDC $r$-$\phi$ and at least one track in CDC $z$-trigger. Several types are formed depending on the condition for the number of full tracks, opening angle, TSC/TOF hits, and ECL cluster hits.
   

2. Total energy triggers: These are based on the ECL energy sum triggers and vetoed by ECL Bhabha and cosmic triggers.
   

3. Isolated cluster counting trigger: We require four or more ECL isolated clusters, which avoid Bhabha events but still require cosmic veto to reduce the cosmic rate.
   

4. Bhabha triggers: We prescale these triggers depending on the luminosity to keep the rate less than 10 Hz.
   

5. Two-track triggers: These triggers take two or more tracks in CDC $r$-$\phi$ and at least one in CDC $z$-triggers. In order to reduce the rate, these require CDC opening angle, TSC/TOF hits, and ECL energy or clusters.
   

6. Muon triggers: These require two or more CDC $r$-$\phi$ tracks and KLM trigger. The track trigger conditions are loose.
   

7. Monitor triggers: These include a random trigger and prescaled triggers with loose conditions for monitoring purpose.

Triggers 1$\sim$3 are intended to catch multi-hadronic events, which provide a redundancy.

In a typical running condition, the average trigger rate is about 200 Hz. According to increase of the beam current and luminosity during several months of runs, we adjusted the trigger condition and prescale values keeping the average trigger rate less or around 200 Hz. The trigger rate is dominated by the beam background. Fig.  shows the trigger rate as a function of beam current of each electron and positron beam. The contribution of the electron beam dominates over that of positron. The trigger rate due to the collision of the beams is $\sim$40 Hz/10cm$^{-2}$s$^{-1}$ under the present conditions.

The trigger efficiency is monitored from the data using the redundant triggers. Each of the multi-track, total energy, and isolated cluster counting triggers provides more than 96% efficiency for multi-hadronic data samples. The combined efficiency is more than 99.5%.

Figure: Trigger rate as a function of beam current for electron or positron single beam runs (top), and total beam current in a collision run (bottom). Contributions of electron and positron single beams are also plotted for a typical beam current ratio of =1.5.