24 September 2002Paul Dauncey1 Trigger issues for the CALICE beam test Paul Dauncey Imperial College London, UK

24 September 2002Paul Dauncey2 Obvious: no trigger if previous particle within ~1  s 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  S ~ 180ns 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 Trigger requirements

24 September 2002Paul Dauncey3 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 Trigger issues

24 September 2002Paul Dauncey4 Assume for now a simple scintillator trigger Concept works fine for scintillating fibre hodoscope also Define two levels of scintillator logic condition “Activity” and “Trigger” “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 2002Paul Dauncey5 Use Activity to veto Trigger if too close in time If Trigger within ~1  s 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 “Activity” and “Trigger” (cont)

24 September 2002Paul Dauncey6 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  s sensitive time? If low, then can be neglected Cosmic pollution?

24 September 2002Paul Dauncey7 BaBar ECAL beam test trigger logic Example of trigger including some of the elements suggested here

24 September 2002Paul Dauncey8 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??? Different Triggers

24 September 2002Paul Dauncey9 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? Logic implementation

24 September 2002Paul Dauncey10 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 UK trigger board

24 September 2002Paul Dauncey11 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 Main questions