Level-3 Trigger Strategy

This page will collect the currently planned running times/intensities for GlueX and the expected event rates. A set of requirements for the Level-3 trigger can be collected based on this information to document the design and implementation strategy.

Phase II and III Planning

After the initial Phase I running period designated for detector commissioning the first "physics" running periods are Phases II and III, which both have a nominal photon flux in the coherent peak (8.4-9 GeV) of $10^{7}$. The expected Level-1 trigger rate for these periods is expected to be at or below 20 kHz, and therefore it is possible to write the entire dataset to tape with an minimum-bias type L1 trigger. Therefore, during these running periods the goal is to commission the Level-3 trigger for future running periods by:

• Run a Level-3 trigger algorithm in pass-through mode on a subset of nodes in the monitoring farm.
• Tag events in the data which satisfy the algorithm requirements to allow studies offline of the:
  • Trigger efficiency in the data with full offline reconstruction
  • Rate reduction factor

Phase IV Planning

This is the first phase of GlueX running where the Level-3 trigger is required to reduce the even rate beyond the reduction provided in hardware by the Level-1 trigger. The nominal photon flux in the coherent peak for this phase is $5x10^{7}$, which is expected to result in a Level-1 trigger rate of around 100 kHz based previous studies. Based on the event size and DAQ bandwidth expectations in Table 2 (below), the event rate to tape is limited to 20 kHz. Therefore, the goal of the Level-3 trigger in Phase IV is to reduce the Level-1 trigger rate by a factor of 5 to 20 kHz.

Assumptions for Level-3 Trigger Planning

Some assumptions are necessary to plan for the requirements of the Level-3 trigger based on the expected running conditions of the experiment. Below are two tables with some assumptions for the data taking conditions for the GlueX experiment.

Table 1: Planned GlueX Running Periods (from PAC 40 Proposal)

	Phase I	Phase II	Phase III	Phase IV	Maximum Intensity
Approved PAC days	30	30	60	200	0
Minimum electron energy (GeV)	10	11	12	12	12
Photon flux in coherent peak (photon/s)	$10^{6}$	$10^{7}$	$10^{7}$	$5x10^{7}$	$10^{8}$
Expected total hadronic event rate (kHz)	??	??	36	180	360
Expected hadronic event rate in coherent peak (kHz)	??	??	1.6	8	16
Level-1 trigger rate (kHz)	2	20	20	100	200

Table 2: Data rate assumptions for GlueX

Event size	15 kB
DAQ bandwidth to write events to tape	300 MB/s