The CMS Trigger

Cross Sections and Rates Cross sections for different processes vary by many orders of magnitude inelastic: 109 Hz W -> ln: 100 Hz tt: 10 Hz Higgs (100 GeV): 0.1 Hz Higgs (600 GeV): 0.01 Hz Required selectivity 1 : 10 10 - 11 Trigger - C.-E. Wulz C.-E. Wulz

Principle of Triggering Event accepted? YES NO Successive steps Depends on Event type Properties of the measured trigger objects Trigger objects (candidates): e/g, m, hadronic jets,t-Jets, missing energy, total energy Trigger conditions: according to physics and technical priorities C.-E. Wulz

CMS Detector (Compact Muon Solenoid) C.-E. Wulz

Trigger Levels in CMS Level-1 Trigger Macrogranular information from calorimters and muon system (e, m, Jets, ETmissing) Threshold and topology conditions possible Latency: 3.2 ms Input rate: 40 MHz Output rate: up to 100 kHz Custom designed electronics system High Level Trigger (several steps) More precise information from calorimeters, muon system, pixel detector and tracker Threshold, topology, mass, … criteria possible as well as matching with other detectors Latency: between 10 ms and 1 s Input rate: up to 100 kHz Ouput (data acquisition) rate: approx. 100 Hz Industral processors and switching network C.-E. Wulz

Conventional Concept with 3 Steps Investment in specialized processors, control C.-E. Wulz

CMS Concept with 2 Steps Advantages: Fewer components, scalable Investment in band width and commercial components Advantages: Fewer components, scalable C.-E. Wulz

Evolution of Trigger Requirements ATLAS/CMS: Rather high rates and large event sizes Interaction rates: ~ Factor 1000 larger than at LEP, ~ Factor 10 larger than at Tevatron C.-E. Wulz 8 Split, Oct. 2002

Level-1 Trigger Only calorimeters and muon system involved Reason: no complex pattern recognition as in tracker required (appr. 1000 tracks at 1034 cm-2s-1 luminosity), lower data volume Trigger is based on: Cluster search in the calorimeters Track search in muon system C.-E. Wulz

Architecture of the Level-1 Trigger GLOBAL TRIGGER Global Calorimeter Trigger Global Muon Trigger Regional Calorimeter Trigger Regional DT Trigger Regional CSC Trigger RPC Trigger Local Calorimeter Trigger Local DT Trigger Local CSC Trigger RPC Hits Calorimeter cell energies DT Hits CSC Hits C.-E. Wulz

Strategy of the Level-1 Trigger Local Energy measurement in single calorimeter cells or groups of cells (towers) Determination of hits or track segments in muon detectors Regional Identification of particle signature Measurement of pT/ET (e/g, m, hadron jets, t-jets) Determination of location coordinates (h,f) and quality Global Sorting of candidates by pT/ET, quality and retaining of the best 4 of each type together with location and quality information Determination of SET, HT, ETmissing, Njets for different thresholds and h ranges Algorithm logic thresholds (pT/ET, NJets) geometric correlations - e.g. back-to-back events, forward tagging jets - more detailed topological requirements optional - location information for HLT - diagnostics C.-E. Wulz

Level-1 Calorimeter Trigger Goals Identify electron / photon candidates Identify jet / t-jet candidates Measure transverse energies (objects, sums, missing ET) Measure location Provide MIP/isolation information to muon trigger C.-E. Wulz

Local / Regional Electron/Photon Trigger Trigger primitive generator (local) Flag max of 4 combinations (“Fine Grain Bit”) Regional calorimeter trigger ET cut Hit +max of > ET threshold Longitundinal cut hadr./electromagn. ET / < 0.05 Hadronic and electromagnetic isolation < 2 GeV One of < 1 GeV h f Jet e/g Electron / photon C.-E. Wulz

Typical e/g Level-1 Rates and Efficiencies Single isolated e/g rate at 25 GeV threshold: 1.9 kHz 95% efficiency at 31 GeV C.-E. Wulz

Jet / t Trigger Jet ET is obtained from energy sum of 3 x 3 regions - sliding window technique, seamless coverage up to |h| < 5 Up to |h| < 3 (HCAL barrel and endcap) the regions are 4 x 4 trigger towers Narrow jets are tagged as t-jets in tracker acceptance (|h| < 2.5) if ET deposit matches any of these patterns { C.-E. Wulz

Typical Level-1 Jet Rates and Efficiencies Single jet rate at 120 GeV threshold: 2.2 kHz, 95% efficiency at 143 GeV Dijet rate at 90 GeV: 2.1 kHz 95% efficiency at 113 GeV Single t-jet rate at 80 GeV threshold: 6.1 kHz C.-E. Wulz C.-E. Wulz 16 Split, Oct. 2002

HT Trigger HT, which is the sum of scalar ET of all high ET objects in the event is more useful than total scalar ET for the discovery or study of heavy particles (SUSY sparticles, top): Total scalar ET integrates too much noise and is not easily calibrated At Level-1 tower-by-tower ET calibration is not available However, jet calibration is available as f(ET, h, f) Implemented in Global Calorimeter Trigger Rate with cutoff at 400 GeV: 0.7 kHz, 95% efficiency at 470 GeV C.-E. Wulz

Muon Trigger Detectors Drift Tube Chambers and Cathode Strip Chambers are used for precision measurements and for triggering. Resistive Plate Chambers (RPC’s) are dedicated trigger chambers. C.-E. Wulz

Local Muon Trigger Drift Tube Chambers Cathode Strip Chambers Superlayer Vector of 4 hit cells Comparators allow resolution of 1/2 strip width Station Correlator combines vectors to track segment 6 hit strips form track segment C.-E. Wulz

Regional DT/CSC Muon Trigger (Track Finder) Trigger relies on track segments pointing to the vertex and correlation of several detector planes Tracks with small pT often do not point to the vertex (multiple scattering, magnetic deflection) Tracks from decays and punchthrough do not point to vertex in general Punchthrough and sailthrough particles seldom transverse all muon detector planes C.-E. Wulz

Regional DT/CSC Muon Trigger (Track Finder) Longitudinal plane Track Segment and direction of extrapolation Bending plane Drift Tube Trigger (CSC Trigger similar) C.-E. Wulz

Regional RPC Muon Trigger RPC-Trigger is based on strip hits matched to precalculated patterns according to pT and charge. 4/4 3/4 High pT Low For improved noise reduction algorithm requiring conincidence of at least 4/6 hit planes has been designed. Number of patterns is high. FPGA solution (previously ASICs) seems feasible, but currently expensive. Solutions to reduce number of patterns under study. C.-E. Wulz

Global Muon Trigger DR/CSC/RPC: combined in Global Muon Trigger Optimized algorithm (no simple AND/OR) with respect to efficiency rates ghost suppression -> Make use of geometry + quality C.-E. Wulz

L1 Single & Di-Muon Trigger Rates Trigger rates in kHz |h| < 2.1 18, 8;8 eW =84.9 % eZ =99.7 % eBsmm = 7.2 % 20, 5;5 eW =82.3 % eZ =99.7 % eBsmm =15.1 % 14, -;- eW =89.6 % eZ =99.8 % eBsmm =27.1 % 25, 4;4 eW =74.2 % eZ =99.5 % eBsmm =18.4 % working points compatible with current L1 pT binning L = 2x1033cm-2s-1 L = 1034cm-2s-1 C.-E. Wulz

Global/Central Trigger within ATLAS and CMS Algorithm bits Algorithm bits Thresholds already set in calorimeters and muon system. The Central Trigger Processor receives object multiplicities. It does not receive location information, therefore topological conditions are impossible. Separate RoI electronics for the Level-2 Trigger is necessary. Thresolds set in Global Trigger. The processor receives objects with location information, therefore topological conditions are possible. Special HLT algorithms or lower thresholds can be used for selected event categories. Sorting needs some time, however. C.-E. Wulz

Global Trigger The trigger decision is taken according to similar criteria as in data analysis: Logic combinations of trigger objects sent by the Global Calorimeter Trigger and the Global Muon Trigger Best 4 isolated electrons/photons ET, h, f Best 4 non-isolated electrons/photons ET, h, f Best 4 jets in forward regions ET, h, f Best 4 jets in central region ET, h, f Best 4 t-Jets ET, h, f Total ET SET Total ET of all good jets HT Missing ET ETmissing, f(ETmissing) 12 jet multiplicities Njets (different ET thresholds and h-regions) Best 4 muons pT, charge, f, h, quality, MIP, isolation Thresholds (pT, ET, NJets) Optional topological and other conditions (geometry, isolation, charge, quality) C.-E. Wulz

Algorithm Logic in Global Trigger Object Conditions Logical Combinations 128 flexible parallel running algorithms implemented in FPGA’s. Trigger decision (Level-1-Accept) is a function of the 128 trigger algorithm bits (for physics). 64 more technical algorithms possible. C.-E. Wulz

Bs -> mm: Example of Topological Trigger D- distributions Dh similar. Can ask for opposite charges in addition. C.-E. Wulz

Bs -> mm: Example of Topological Trigger Topological conditions: Dh < 1.5, D < 2 rad, opposite muon charges Gain by topological conditions and requiring no threshold on second muon with respect to working point 20; 5,5: 1 kHz rate, 7.8%efficiency (15.1% without, 22.9% with cuts). C.-E. Wulz

High Level Trigger Goals Validate Level-1 decision Refine ET/pT thresholds Refine measurement of position and other parameters Reject backgrounds Perform first physics selection Detailed algorithms: see talks of A. Nikitenko (e/g,jets), N. Neumeister (m) and other talks related to CMS physics and wait for DAQ/HLT TDR due Dec. 2002. C.-E. Wulz

High Level Trigger Challenges Rate reduction Design input rate: 100 kHz (50 kHz at startup with luminosity 2x1033 cm-2s-1), i.e. 1 event every 10 ms. Safety factor of 3: 33 kHz (16.5 kHz). Output rate to tape: order of 100 Hz Reduction factor: 1:1000 Example of allocation of input bandwidth to four categories of physics objects plus service triggers (1 or 0.5 kHz): electrons/photons (8 or 4 kHz) muons (8 or 4 kHz) t-jets (8 or 4 kHz) jets + combined channels (8 or 4 kHz) Algorithms The entire HLT is implemented in a processor farm. Algorithms can almost be as sophisticated as in the off-line analysis. In principle continuum of steps possible. Current practice: level-2 (calo + muons), level-2.5 (pixels), level-3 (tracker), full reconstruction. C.-E. Wulz

High Level Trigger and DAQ Challenges Processing time Estimated processing time: up to 1 s for certain events, average 50 ms About 1000 processors needed. Interconnection of processors and frontend Frontend has O(1000) modules -> necessity for large switching network. Bandwidth Average event size 1 MB -> For maximum L1 rate need 100 GByte/s capacity. C.-E. Wulz

Conclusions CMS has designed a Trigger capable of fulfilling physics and technical requirements at LHC. The Trigger consists of 2 distinct levels. Level-1 is custom designed, the HLT is implemented with industrial components. Prototypes of many Level-1 electronics boards exist. Integration and synchronization tests are scheduled for 2003/2004. The HLT/DAQ Technical Design Report is finalized and due to be ready at the end of 2002. C.-E. Wulz 33

Acknowledgments my colleagues in CMS and at HEPHY Vienna, especially P. Chumney, J. Erö, S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, A. Taurok. to the Organizing Committee of LHC Days in Split for the invitation and the enjoyable conference. C.-E. Wulz