Triggering at High Luminosity at CDF
Tom WrightUniversity of Michigan
Fermilab All-Experimenters’ MeetingAugust 3, 2009
The CDF Trigger System• Three-level system
• Synchronous Level 1– 100% hardware– Guaranteed latency
• Asynchronous Level 2– Hardware/software hybrid– Limited buffer space– Can incur deadtime
• Input from L1 too high• Output too high for DAQ
• Level 3– Fast offline reconstruction– No problem with capacity so far
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Trigger Objects• Level 1 & 2 can use almost all
subsystems of CDF– Tracking (fast lookup table)– Calorimetry (electrons, photons,
jets, missing ET)
– Muon stubs / scintillators– Silicon tracking (Level 2 only)
• Level 1 has simple matching (muons, electrons) and can do coincidences
• Level 2 allows more complex matching and correlations on the same inputs (plus silicon tracks)– All data delivered to a PC, can
implemented any desired algorithm in software
3JDL 11/15/07PJW 9/23/98
CDF Trigger Menus• Goal is to keep ‘signal’ triggers unprescaled
– High-pT inclusive leptons, photons, missing ET, high-ET jet, multijet, etc
• At lower luminosity, start enabling more triggers– Medium-pT leptons, b-physics leptons, etc
– Looser versions of signal triggers
• At lowest luminosity, switch on hadronic b-physics triggers
• Variety of backup triggers on fixed prescales (jets, tracks, etc)– Low-bias samples for measuring ID fake rates / efficiencies
• Monitor and control Level 1 and Level 2 rates to manage deadtime– Target is 5%– Trade-off between high efficiency and high utilization (events on tape)
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Dynamic Prescaling (DPS)
• Main tool for managing rates
• DPS triggers start at a specified maximum prescale to keep rate low
• As luminosity falls, prescales are reduced as bandwidth becomes available
• Prescale adjustments based on feedback from total L1/L2 rates
• Prioritization based on maximum prescale and individual rates– Lowest-rate trigger prescales are
adjusted first
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Trigger Rates
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low-pT dimuons
hadronic b-physics
bit over our target rate
Store 6832Feb 2009L = 335E30
changing DPSto maintain rate
Total Deadtime
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Stick pretty close to our goal up to ~310E30Somewhat higher above that (from high Level 2 output rate)
Data-Taking Efficiency
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Amount of luminosity we see above 310E30 small (so far)Initial deadtime doesn’t have large impact on our efficiency
average of store efficienciesversus store initial luminosity
Trigger Menu Evolution
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• A sample of menus from the past year• Tighten / prescale at high luminosity to
keep up with the Tevatron• Haven’t had to sacrifice a lot so far,
trimmed backups or added new requirements with high efficiency
• Continue this process if/when Tevatron performance improves further
Conclusion
• The CDF trigger/DAQ system has worked well as luminosity increases
• High-priority signal triggers have remained unprescaled• Triggers on dynamic prescale seeing 50-90% of available integrated luminosity• Continue to collect sufficient backup triggers
• Gradual improvements to trigger menu have allowed us to keep up• Headroom exists to continue this process if necessary, without large impact on our
core high-pT physics program
• Increasing luminosity also impacts b-physics program, particularly hadronic triggers• Spending much less time at low luminosities where those triggers are active
– Yields have dropped by ~25% for B , ~80% for Bhh over past few years• Focus of most of the recent work on the trigger menu
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Backup
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High-Rate Triggers• Most difficult is ‘CMX’ muons
– 0.6 < |h| < 1.0– Have had this on DPS in the past
• Next is missing ET plus dijet
– Higgs/diboson trigger• Should be able to keep these and
other signal triggers live if luminosity increases further
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Sample Store Profile
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