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 . 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 , 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.
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) | |||||
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 |