The CMS Level-1 Trigger System Dave Newbold, University of Bristol On behalf of the CMS collaboration

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Triggering at the LHC Tiny signals, huge background p-p inelastic rate: ~ GHz e.g. H(150) ->  : < mHz …but bb ~MHz – background! Complex events & detector Typical CMS event is >1MB Max storage rate : 100MB/s Huge selectivity needed Trigger reduction factor: 10 7 [L1 o/p rate < 100kHz] LHC 40MHz Mean of 23 evts per BX at full luminosity Detector response & time of flight are > 1BX

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Level-1 trigger strategy Driven by LHC physics conditions Decays of rare and heavy particles against large “soft” QCD b/g Many decays involve intermediate W / Z; H ->  also important -> Identify high-p t leptons* and photons (*including  ) Low p t thresholds motivated by efficiency for W / Z / light Higgs Trigger combinations >20GeV limit on single-lepton thresholds due to quark decay +  0 b/g Most interesting states decay to two or more trigger objects – can use lower thresholds for objects in combination -> Find trigger objects locally, combine and cut only at last stage Large uncertainties in background (and perhaps signal) Flexibility and control of rate are both vital -> All trigger thresholds and conditions must be programmable Trigger architecture is fixed, but this is a function of detector geometry Must have high and well-understood efficiency -> Need to include overlapping and minbias triggers to measure 

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Trigger / DAQ architecture Level-1 uses muon & calo data only Tracking data too large / complex Local pattern recognition is possible Fully pipelined digital electronic system Physically impossible to make decision in 25ns (speed of light) All data stored on detector during fixed L1 latency, read out upon L1A Memory constraints give max latency 3.2  s (of which 2  s is cable delay) Output of Level-1 Single bit: accept / reject Triggers may be ‘throttled’ for technical reasons – but otherwise, zero deadtime On L1A, data proceed via event builder switch to High Level Trigger (see talk of G. Bagliesi)

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Level-1 overview

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Trigger system location

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 ECAL, HCAL cover to  =  3, forward calorimeter to  =  5 Trig prims group crystals / scintillators into (2 x) 32 x 72 trigger towers Calorimeter trigger detectors

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Calorimeter trigger algorithms

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Calorimeter trigger performance Full GEANT study Includes minbias background L=10 34 cm -2 s -1 Efficiencies For objects within fiducial acceptance Rates e/  dominated by jet (  0 ) background Steep curves allow good control of rate

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Muon trigger detectors Dedicated RPC detectors Excellent time resolution for effective BX-ID Main DT and CSC detectors Excellent position resolution for accurate p t reconstruction

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Muon trigger algorithms

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Muon trigger performance Efficiency for any muon >3 GeV p t

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Global trigger Global trigger implements a wide range of triggers (incl. topological) Example low lumi (L= cm -2 s -1 ) trigger selection shown above Total rate balanced between e/g, jets, muons for initial HLT input 50kHz Rate safety factor ~3, to account for uncertainties in background Trigger typeThrsh (0.95 eff)Rate (kHz)Cum. Rate (kHz) Incl. iso e/  29 GeV3.3 Di- e/  17 GeV Incl. iso  14 GeV/c Di-  3 GeV/c Single  86 GeV Di-  59 GeV j, 3j, 4j177, 86, 70 GeV j && E t miss 88 ; 46 GeV e/ , j 21 ; 45 GeV Minbias, calib, efficiency estimation

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Physics efficiencies Typical efficiencies for preceding trigger L= cm -2 s -1 ChannelEfficiency %Efficiency % from each trigger type – (each) cumulative W - > e 70 e: (70) 70 t -> eX91 e: (82) 82 e.  (62) 86  : (55) 89 jjj: (24) 90e.j: (54) 91 Z -> ee94 e: (93) 93e.e: (76) 94 H(115) -> gg99 e: (99) 99e.e (82) 99 H(150) -> WW87 e: (78) 78 e.  (43) 81  : (34) 83 e.j: (39) 85j: (28) 87 H(135) ->  -> ej 84 e: (70) 70 e.  (62) 86 e.j: (54) 91  : (38) 84 j: (34) 84 Charged H(200)98  : (85) 85 jj: (77) 96j. E tm : (60) 98 H(200) ->  -> jj 81  : (75) 75  : (50) 79 j: (24) 81jj: (9) 81 H(500) ->  -> jj 99  : (94) 94  : (64) 94 j: (94) 99jj: (73) 99 t -> jets53 H t : (39) 39jjjj: (26) 43jjj: (26) 46jj: (21) 47j: (35) 53 mSUGRA99 j: (99) 99 H(120) -> bb41 jjj: (12) 12j: (27) 30  : (26) 41 jj: (16) 41 Invisible H(120)44 j. E tm : (39) 39j: (22) 41  : (13) 44

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Practical challenges Technology Pushing (today’s) digital processing and comms technologies to the limit Cannot afford huge outlay on custom components (-> FPGAs) System must last for 10+ years: obsolescence. Synchronisation Time-of-flight and detector response take many BX Subdetector timing and bunch-crossing ID will be challenging Reliability Level-1 trigger performs online selection: cannot correct mistakes System must be highly reliable, all data taking depends on it But some parts will fail or degrade at some time Some components on detector -> radiation, magnetic field considerations Simulation / configuration control / real-time trigger optimisation Trigger integration for CMS begins the real work starts now

Dave Newbold, University of BristolHEP2003 Conference - 19/7/2003 Summary Triggering at the LHC will be hard Leptons / photons are the key CMS Level-1 trigger system currently under construction Reduces 40MHz BX rate to < 50KHz L1A Very large digital logic system Uses calorimeter and muon information only Simulated performance shows good efficiency for the interesting channels