Level-3 Trigger Strategy
Contents
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 will 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 . 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 a minimum-bias type L1 trigger. Therefore, during these running periods the goal is to commission the Level-3 trigger for future running periods by:
- Running a Level-3 trigger algorithm in pass-through mode on a subset of nodes in the monitoring farm.
- Tagging events in the data stream which satisfy the algorithm requirements to allow studies offline of the:
- Trigger efficiency in the data with full offline reconstruction
- Rate reduction factor to verify it meets the requirements for future running
Phase IV Planning
This is the first phase of GlueX running where the Level-3 trigger is required to reduce the event rate beyond the reduction provided in hardware by the Level-1 trigger. The nominal photon flux in the coherent peak for this phase is , which is expected to result in a Level-1 trigger rate of around 100 kHz based on previous studies. Given the event size and DAQ bandwidth expectations in Table 2 (below), the event rate written 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, while accepting all exotic-meson candidates produced in the coherent peak.
Full Intensity Planning
The intensity from the GlueX design goal was for a photon flux in the coherent peak of , but the optimal photon flux may depend on many factors including beam conditions, pileup, etc. An additional complication of the full intensity running is that it may not be possible to record all the hadronic events in the coherent peak in the allowed 20 kHz of DAQ to tape bandwidth. Therefore, a more selective sample of hadronic events would need to be chosen, such as identifying strangeness candidates via displaced vertices or an upgraded forward PID detector. This will require further studies in the future, but is not currently a high priority for the Trigger Working Group.
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.
Phase I | Phase II | Phase III | Phase IV | Full 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) | |||||
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 |
Event size | 15 kB |
DAQ bandwidth to write events to tape | 300 MB/s |