1. Trigger issues for the CALICE beam test
Paul Dauncey
Imperial College, University of London, UK
24 September 2002
Paul Dauncey

2. Trigger requirements
Need clean data to compare carefully with simulation
No double particle events, beam halo, cosmics, etc.
Must veto any events with more than one particle
Obvious: no trigger if previous particle within ~1ms
Less obvious: no trigger if following particle with ~150ns, i.e. before VFE sample-and-hold time
CR-RC shaping in units of shaping time tS ~ 180ns
24 September 2002
Paul Dauncey

3. Trigger issues Want to discuss the issues for triggering here
No commitment for providing trigger yet (certainly not from the UK!)
I hope this starts a discussion of what will be needed
UK interest here as we are building readout electronics and DAQ which uses the output of the trigger logic
Soon need to decide what logic goes where
I will describe a possible system
“Straw man” proposal to get people thinking
How much we actually use is still to be decided
24 September 2002
Paul Dauncey

4. “Activity” and “Trigger”
Assume for now a simple scintillator trigger
Concept works fine for scintillating fibre hodoscope also
Define two levels of scintillator logic condition
“Activity”; OR of hits in the scintillators, i.e. any activity
“Trigger”; AND of hits in the scintillators, i.e. good central beam particle
24 September 2002
Paul Dauncey

5. “Activity” and “Trigger” (cont)
Use Activity to veto Trigger if too close in time
If Trigger within ~1ms of last Activity, then prevent Trigger from being issued
If Activity within ~150ns of Trigger, then abort Trigger
Cannot hold Trigger during the ~150ns as it must reach the VFE chip in time to produce sample-and-hold (~180ns)
Electronics must allow Trigger without subsequent readout
Only other possibility is to read out state of Activity and not use events with it set when reading offline
Need to be aware of “race condition”!
Trigger clearly also produces Activity so must be sure it does not kill itself
Requires careful signal shaping/timing
24 September 2002
Paul Dauncey

6. Cosmic pollution?
Do we need to include “cosmics” top-bottom scintillators in the Activity logic OR so as to veto events with a cosmic as well?
Will scintillator fit under support table for calorimeters?
Risk of bias by vetoing events with large showers leaking out of sides?
What is the cosmics probability to be in time with our few ms sensitive time? If low, then can be neglected
24 September 2002
Paul Dauncey

7. BaBar ECAL beam test trigger logic
24 September 2002
Paul Dauncey

8. Different Triggers Do we want other trigger conditions besides beam?
Cosmics? (Now selecting them!)
Anti-beam (i.e. noise events)?
Clock trigger?
Any others?
Should these be parasitic between beam bunch trains?
Exactly equivalent conditions as data taking
Makes control more complex
Need VME control of trigger type
From where? UK electronics???
24 September 2002
Paul Dauncey

9. Logic implementation Where will the vetos and aborts be done?
Activity preventing Trigger needs
Logic to generate veto
Trigger aborted by Activity needs
Logic to generate abort or
VME interface to read out Activity status
What are the signal levels to be used?
NIM? LVDS? TTL?
We need to be able to plug the cables into the UK crate
How much of this logic should be in the UK electronics?
24 September 2002
Paul Dauncey

10. UK trigger board
Single board which handles trigger input to UK electronics
Distribution to readout boards within crate (and elsewhere?)
Holds off further triggers until readout complete
Hold off is reset via VME at end of event read
Minimum functionality needed
Inputs: Trigger, Abort; from trigger logic. All other timing, veto, abort etc. done in NIM
Output: Hold; to trigger NIM logic to prevent further triggers
Maximum extra functionality we might add
Input: Trigger, Activity; all veto, abort, etc. done in logic on trigger board
Also need to decide how to select different types of trigger
More VME-controlled output levels? How many?
Hard to build a general trigger board to cover both extremes…
…and even harder to cover all possibilities between them
24 September 2002
Paul Dauncey

11. Main questions What are the requirements for the trigger?
Different types?
Different veto conditions?
Who will supply the hardware?
Scintillators, PMT’s, HV power supplies, NIM (or similar) trigger logic units, etc?
How much will be common to the beam position system?
Do we want post-trigger abort in hardware or software?
Timescale to decide must be soon!
UK should be building trigger board (one off) in ~7 months
Needed to test prototype readout boards
Must know functionality of trigger board with ~2 months
24 September 2002
Paul Dauncey