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The CMS Level-1 Trigger: System and Operation

The CMS Level-1 Trigger: System and Operation. Christian Hartl (CERN) on behalf of CMS. SPG-ÖPG, Lausanne, 15 June 2011. In this talk. 1. Basics 2. Triggering at CMS 3. Level-1 Trigger System 4. Operational Experience.

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The CMS Level-1 Trigger: System and Operation

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  1. The CMS Level-1 Trigger:System and Operation Christian Hartl (CERN) on behalf of CMS SPG-ÖPG, Lausanne, 15 June 2011

  2. In this talk • 1. Basics • 2. Triggering at CMS • 3. Level-1 Trigger System • 4. Operational Experience

  3. Early experiments in particle physics observed phenomena of interest directly. counting experiments no trigger Later experiments to spot rare events by eye e.g. bubble chamber pre-trigger to take snapshot in right moment (no events rejected online) trained analysts scanned up to 250k photos/month! Rutherford's Gold Foil Experiment 1909 omega-minus 1967 @ BNL Before triggering The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  4. Triggering for physics at LHC LHC design energy and luminosity: • looking for extremely rare signals • standard model physics = background • e.g. 1013 inelastic p-p collisions compared to one HSM 4µ • can't record everything • must reject background • must remain efficient for signal • need to decide fast • to avoid dead-time • How? The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  5. electrical signals from detectors are combined to define trigger signal "traditional approach" trigger signal causes digitization and recording of data no further trigger possible until data on tape (dead time penalty) NIM logic modules O(10) operations per module AND OR NOT threshold delay electronic chips (FPGA, ASIC) O(104) logic operations per chip dead-time fraction =trigger rate x readout time Simple concepts back then today The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  6. intermediate readout buffer(s) fast local readout, reduced dead-time after trigger bunch crossing clock as pre-trigger in hadron colliders time between bunch collisions used to calculate trigger decision several trigger levels fast (low-latency) early level(s), advanced later level(s) Pipelined trigger and readout process several events simultaneously in a pipeline (triggering & readout) prevents long dead-time after accept in early trigger stage more channels  less occupancy deal with pile-up at LHC luminosities several proton-proton interactions may pile up in a bunch crossing Aleph @ LEP Multi-level triggering – from LEP to LHC needed if: time between bunch crossings << calculation and distribution of trigger decision new in LHC already in LEP The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  7. In this talk • 1. Basics • 2. Triggering at CMS • 3. Level-1 Trigger System • 4. Operational Experience

  8. CMS at LHC The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  9. LHC design collisions p-p (Pb-Pb) √s=14 TeV (Pb-Pb: 5.52 TeV) 40 MHz bunch collision rate 25 ns spacing (LEP: 22 µs) 2835/3564 slots filled luminosity 10 Hz/nb 1011 p/bunch average pile-up =18 events/bunch crossing Level-1: 40 MHz  100 kHz custom electronics based on FPGAs and ASICs massive parallel pipeline,fixed latency (~3.2 µs) decision based on coarse calorimetric and muon data High Level Trigger:100 kHz  300 Hz CPU farm running algorithms processing time depends on event complexity (~40 ms) decision based on full detector data,seeding on Level-1 info 40 MHz 100 kHz 300 Hz to tape CMS uses two trigger levels data acquisition scheme L1-HLT throughput: 100 GB/s The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  10. In this talk • 1. Basics • 2. Triggering at CMS • 3. Level-1 Trigger System • 4. Operational Experience

  11. channels used: calorimeter systems muon detectors beam monitoring systems tracker channels NOT used construction of trigger objects: "local"  "regional"  "global" applying cuts only at global trigger level Level-1 Global Trigger: receives four best objects of each kind checks 128 programmable conditions: object multiplicity, transverse momentum & energy, position, quality, topology checks 64 technical trigger conditions: signals provided by sub-detectors combines conditions in final OR with mask and prescales Level-1 accept distributed by Trigger Control System according to detector readiness and trigger rules Level-1 trigger approach The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  12. Level-1 trigger architecture Calorimeter Trigger Muon Trigger DAQ ||<3 0.9<||<2.4 ||<1.2 ||<3 0<||<5 • RPC = resistive plate chambers • CSC = cathode strip chambers • DT = drift tubes • ECAL = lead-tungstate e/m calorimeter • HCAL = brass-scintillator hardronic calorimeter • TTC = Timing, Trigger & Control system • TTS = Trigger Throtting system • DAQ = data acquisition system RPC hits CSC hits DT hits ECAL Trigger Primitives HCAL/HF Trigger Primitives Link system Segment finder Segment finder RegionalCalorimeterTrigger Pattern Comparator Track finder Track finder 40 MHz pipeline 4+4 µ 4 µ 4 µ GlobalCalorimeterTrigger Global Muon Trigger MIP + ISO bits 4 µ e, J, ET, HT, ETmiss, HTmiss Global Trigger Level-1 Accept Status TTC system TTS system 32 partitions Detector Frontend The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  13. Custom-built Level-1 trigger hardware Wisconsin Warsaw Florida Bologna Madrid Vienna Resistive Plate Chambers Pattern Comparator Regional Calorimeter Trigger Cathode Strip Chambers Track Finder Drift Tube Track Finder muon objects calorimeter objects: e, J, ET, HT, ETmiss, HTmiss Imperial College Vienna detector status (trigger throttling) Global Calorimeter Trigger Global Trigger Global Muon Trigger Timing Trigger & Control System Fast Merging Modules Level-1 Accept,control signals The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  14. Level-1 trigger objects muon track algorithm(DT Track Finder) electron/photon algorithm (RCT) • match & merge • barrel:DT-RPC • endcap:CSC-RPC • cancel duplicates • overlap region:DT-CSC • sort by momentum and quality Global Muon Trigger algorithm: jet algorithm (GCT) The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  15. Global Trigger, Trigger Control System 40 MHz pipeline FINAL DECISION LOGIC • Every bunch crossing, for which a potential Level-1 accept is inhibited, is counted as dead. • needed to calculate recorded integrated luminosity GLOBAL TRIGGER LOGIC 1. Logic OR 2. Prescale 3. Rate Counters 128xalgos calo & muonobjects CMS regionaltrigger GCTGMT 64xtechnical technical trigger signals(beam monitoring systems etc.) TRIGGER CONTROL SYSTEM rand calib physics random calib deadtime counters L1A candidate backpressure, trigger rules GLOBAL TRIGGER Level-1 Accept (via TTC system to detector) The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  16. Trigger Supervisor (TS) framework based on XDAQ middleware distributed control & monitoring system hardware access basic unit = TS cell main executive,>=1 per subsystem deployed as linux service on machine connected to hardware Services provided by each TS cell hardware configuration interconnection testing monitoring alarming logging database access inter-TS-cell communication AJAX-based web interfaces Level-1 page monitor and start/stop processes central monitoring of important subsystem items speed-dial for important applications current configuration status and identifieres (keys) … Trigger Function Manager interface adapter: Run Control – Level-1 online software Level-1 trigger software system example: configuration service (component diagram) courtesy of Marc Magrans

  17. Level-1 triggerData Quality Monitoring (CMS Data Analysis Software – CMSSW) Level-1 triggerweb applications Level-1 Page RCT TS Cell Trigger Supervisor applications (examples) Central TS Cell GMT TS Cell GT TS Cell The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  18. In this talk • 1. Basics • 2. Triggering at CMS • 3. Level-1 Trigger System • 4. Operational Experience

  19. Optimized synchronization of Level-1 trigger systems  efficiency increase Trigger performance good in first 2010 run Level-1 and HLT trigger menus continuously adapted to LHC conditions Below ~ 0.4 Hz/µb minimum-bias trigger simple threshold cuts no (little) pre-scaling Up to 200 Hz/µb (end of 2010) triggers based on physics objects controlling rates with prescales effects from pile-up, detector etc. Good start in 2010 example: RPC trigger w.r.t. mininum-bias trigger nominal trigger cut:5 GeV example: DT trigger performance (from J/Psi) 348 bunches colliding 150 ns bunch spacing 43 pb-1 collected in 2010 (p-p)

  20. 2011 – Level-1 trigger improvements for example: • better muon algorithms • DT ghost busting • RPC pattern recognition • better energy resolution in calorimeter trigger • electron energy corrections • jet energy corrections • improved online software stability • avoid operational downtime (many bottlenecks) • veto triggers that pre-fire (25 ns early, 5% of time) • pre-firing kills collision events (trigger rules disallow two consecutivee triggers) • avoid this: veto on signal from BPTX (electrostatic beam-pickup), advanced by 25 ns The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  21. 2011 – experience and outlook • Very good performance of Level-1 & HLT • smooth & efficient operations • > 850 pb-1 (p-p @ 7 TeV) recorded • continous improvements • excellent work in hardware, software, analysis, trigger menu development • Steep increase in luminosity • peak lumi > 1.25 Hz/nb (1042 bunches colliding) • current menu is for 1.4 Hz/nb • possibly reach 5 Hz/nb in 2011 • best wishes to the LHC! physics priorities luminosity Level-1 and HLT trigger menus are steadily evolving. physics results control rates The CMS Level-1 Trigger @ SPG-ÖPG 2011, Lausanne

  22. Thank you

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