Understanding GLAST Large Area Telescope Trigger Primitive Signals

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope Trigger Primitive Signals: One-shot || Fast-Or..? Dave Lauben dave.lauben@stanford.edu

2. Tracker Trigger Primitives: Outline 1. Charge deposition, threshold walk, & pulse width • We all know about it, how are we handling it? • Some unexamined results from the Beamtest 2. Single One-shots …In the foot, or in the head? • How one-shots are helpful • How one-shots are insidious 3. Comparing Strip Hits with Fast-Or Capture… • Difference for Positrons vs. Photons 4. (One-shots || Raw-Fast-Or) …what gain, what cost? • Maintains layer livetime even if noisy strips • Occasional multi-triggers from heavy ions

3. Charge Dep., Thresh., TOT & One-shots 1. One-shot triggers on rising edge (1 us width) 3. One-shot can not Re-trigger until TOT first drops low again 4. The difficulty is that any random noise which activates the one-shot w/in ~Mip TOT-width-time just before a real event causes that layer to behave as if DEAD. This is a form of trigger inefficiency not explicitly measured by the DAQ. Layer rate counters give at best only an approximate measure of this inefficiency. 2. One-shot clearly helps for fractional Mips signal

4. Btem/Bfem Trigger and Fast-Or Capture 5. One-shots (1 us, edge triggered) Bfem Trigger was designed to capture the Fast-Or’s causing the first occurrence of 3xy, at the possible cost of missing late Fast-Or’s arriving >50ns after the first 3xy goes true…

5. mask mask mask mask mask mask Time Fast-Or, Hit Latch, Readout (Flight~Bfem) -64- -64- -64-

6. Captured Low Captured High Bfem Fast-Or Capture: No Mercy for Late Treq’s! But, tracks at normal incidence suffer only threshold walk!

7. Beamtest: Fast-Or vs. Strip Hit Efficiencies 20 GeV Positrons, Normal Incidence 20 GeV Photons, Normal Incidence Y7: Extra Hits with Reduced Fast-Or for positrons Layer-Any-Hit Counts photon convert layer effect? Y7: Extra Hits with Enhanced Fast-Or for photons Fast-Or Capture Counts

8. Raw Fast-Or Signal (straight from Tracker) Quiet: true livetime is 99.95%. If livetime estimated from 7 rising edges at ~10 us ea. over 80ms span gives 99.91% est. livetime, Rate counter is 0.04% pessimistic. Quiet Layer (just cosmics) Noisy: true livetime is 74.48%. If livetime estimated from 940 rising edges at ~10 us ea. over 80ms span, gives 88.25% est. livetime, Rate counter is +13.5% optimistic. Noisy Layer (minimal mask) Nominal MIP TOT Expanded View Excessive high TOT precludes rising edge when event occurs (one-shot will truncate but can’t add an edge!) This layer is out to lunch for this event! (in fact, it’s 25% dead) Scope captured data acquired at conclusion of Beamtest ’99 One-shot output

9. Layer Livetime Fraction = 1 – Rate x Width Inter-arrival Times Noisy Layer (74.8% live) 100ms 10ms Quiet Layer (99.95% live) TOT Width 1ms 100ms

10. … 12 Gtfe Stages Typical … Fast Or mask 1. Restores observability of raw layer livetime 2. Drastically improves true event throughput in presence of gross noise 3. Minor extra-triggers from e.g. heavy ions One- Shot *Proposed Solution: One-Shot || Fast-Or *Add 2nd signal path to exported Fast-Or One-Shot{ Fast-Or } || (mask & Fast-Or)

11. Trigger Timing Monte Carlo #1 (Simple) 5 kHz event rate, moderate layer noise 4. Coincidence of one-shots gives occasional miss 3. Coincidence of raw Fast-Or does just fine 2. Layer behavior Red: 1-shot output Blue: Raw Fast-Or 1. Photon Events

12. Trigger Timing Monte Carlo #2 (Simple) 5 kHz event rate, extreme layer noise Coincidence of one-shots alone goes blind! Nearly all events lost! Coincidence of raw Fast-Or has minor false rate Noise with Long Tot’s

13. One-Shot || Fast-Or (proposed option) One-Shots Alone Summary: One-Shot vs. Raw Fast-Or While this analysis is very simple, it’s the difference in slope at the zero noise point that’s so bothersome

14. Conclusions 1. Embedding One-shots in Flight Gtrc’s • Better for clean fractional Mip charge deposition • Seriously hinders observability of layer livetime, unless augmented by second signal export path 2. Export (One-shot || Raw-Fast-Or) Benefits • Drastically improves Gamma throughput during long-TOT noise episodes (prior to mask upload) • Preserves ability to measure true layer efficiency 3. Any reason NOT to export || Raw-Fast-Or (see page 10)?

15. Cyberdocs Related to Tracker Fast-Or Lat-Td-019 Haller Trigger and Dataflow Subsystem Specification Lat-Ss-152 R.Johnson Tracker Subsystem Level-IV Readout Elex Spec Lat-Td-153 R.Johnson Tracker Front-end Electronics Lat-Ss-168 R.Johnson Conceptual Design of the Tracker Elex Sys Lat-Ss-169 R.Johnson Tracker Front-end Readout Asic Specification Lat-Ss-170 R.Johnson Conceptual Design of the Tracker Gtrc Lat-Ss-171 D.Nelson Spec. of the Tkr Front-end Multi-chip Module Lat-Td-232 R.Johnson Noise Analysis of the LAT Tracker Amplifier Lat-Td-244 Sadrozinski TOT Requirements for the Tracker Electronics Lat-Td-246 R.Johnson Prototype Testing of the Tkr Front-End Asic Lat-Ss-284 Haller Trigger Level-IV Specification Lat-Ss-285 Haller Dataflow Level-IV Specification Lat-Ss-286 Haller Conceptual Design of the Global Trigger Lat-Ss-287 Haller Conceptual Design of the Elex/Trig/Data Sys Lat-Mr-351 Davis Report for Elex Internal Peer Design Review Lat-Ss-386 R.Johnson Glast LAT Tracker Asics Lat-Td-458 Haller LAT Elex, Daq, Fsw Prelim. Design Report Lat-Pr-513 Davis LAT Elex Pre-PDR Peer Design Rev. Presentation Lat-Td-545 R.Johnson Test Results, Gtfe64D Tkr Front-end Prototype Lat-Ss-560 Russell Global Trigger and Acd Hit Maps Lat-Td-364 Ohyama Single Channel Noise Occupancy in the Btem Lat-Td-603 Sodrozinski Temp. Dependence of EOM Noise in Glast SSD’s Note: List not guaranteed complete. Some documents may have been superceded. Non-Cyberdocs not admissible.