Trigger issues for the CALICE beam test

1
Trigger issues for the CALICE beam test

• Paul Dauncey
• Imperial College London, UK

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

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

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

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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

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 lower 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

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BaBar ECAL beam test trigger logic
Example of trigger including some of the elements
suggested here
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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???

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?

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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 Reset to trigger NIM latch to allow
  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

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Main questions

• What are the requirements for the trigger?
• Different types?
• Different veto conditions?
• Who will supply the hardware?
• Scintillators, PMTs, 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