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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