Four Seas Conference Istanbul, 10 September 2004 Claudia-Elisabeth Wulz Institute for High Energy Physics, Vienna Fast Event Selection at CERN’s Large Hadron Collider

4 Seas, Sep C.-E. Wulz2 Large Hadron Collider C.-E. Wulz LHC SPS CMS TOTEM ATLAS

4 Seas, Sep C.-E. Wulz3 LHC Parameters C.-E. Wulz Proton- Proton Circumference: 27 km Nr. of bunches: Protons / bunch: Beam energy: 2 x 7 TeV Luminosity: cm -2 s -1 Bunch crossing interval: 25 ns Collision rate: 10 7 … 10 9 Hz Magnetic flux density: 8.4 T Number of dipole magnets: ~ 1200 Heavy ions (Pb-Pb, S-S, etc.) Beam energy: up to 5.5 TeV per nucleon pair Luminosity: cm -2 s -1 for lead cm -2 s -1 for oxygen Bunch crossing interval: 125 ns Partons Bunches Protons

4 Seas, Sep C.-E. Wulz4 Cross Sections and Rates - Why we need to select Cross sections for different processes vary by many orders of magnitude Inelastic: 10 9 Hz W  l : 100 Hz tt: 10 Hz Higgs (120 GeV): 0.1 Hz Higgs (500 GeV): 0.01 Hz Required selectivity 1 : Trigger - C.-E. Wulz

4 Seas, Sep C.-E. Wulz5 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 5Split, Oct. 2002

4 Seas, Sep C.-E. Wulz6 Comparisons of LHC, medical and astrophysics Image acquisition Image analysis Image distribution (mammogrid)

4 Seas, Sep C.-E. Wulz7 Event type Properties of the measured trigger objects Event accepted? T( ) YES NO Depends on Trigger objects Trigger objects (candidates):e/ , , hadronic jets,  -Jets, missing energy, total energy Trigger conditions: Trigger conditions: according to physics and technical priorities Successive steps Principle of Triggering

4 Seas, Sep C.-E. Wulz8 Conventional Concept with 3 Steps Investment in specialized processors, control

4 Seas, Sep C.-E. Wulz9 Investment in band width and commercial components Advantages: Fewer components, scalable Concept with 2 Steps (CMS)

4 Seas, Sep C.-E. Wulz10 CMS Detector (Compact Muon Solenoid)

4 Seas, Sep C.-E. Wulz11 Trigger Levels in CMS Level-1 Trigger Macrogranular information from calorimeters and muon system (e, , Jets, E T missing ) Threshold and topology conditions possible Latency: 3.2  s 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

4 Seas, Sep C.-E. Wulz12 Level-1 Trigger Only calorimeters and muon system involved Reason: no complex pattern recognition as in tracker required (appr tracks at cm -2 s -1 luminosity), lower data volume Trigger is based on: Cluster search in the calorimeters Track search in muon system

4 Seas, Sep C.-E. Wulz13 Architecture of the Level-1 Trigger GLOBAL TRIGGER Local Calorimeter Trigger Local DT Trigger Local CSC Trigger Regional CSC Trigger RPC Trigger CSC Hits RPC Hits DT Hits Calorimeter cell energies Global Calorimeter Trigger Global Muon Trigger Regional DT Trigger Regional Calorimeter Trigger

4 Seas, Sep C.-E. Wulz14 Strategy of the Level-1 Trigger Local Energy measurement in single calorimeter cells or groups of cells (towers) Regional Determination of hits or track segments in muon detectors Regional Identification of particle signature Measurement of p T /E T (e/ , , hadron jets,  -jets) Determination of location coordinates ( ,  ) and qualityGlobal Sorting of candidates by p T /E T, quality and retaining of the best 4 of each type together with location and quality information Determination of  E T, H T, E T missing, N jets for different thresholds and  ranges Algorithm logic thresholds (p T /E T, N Jets ) geometric correlations - e.g. back-to-back events, forward tagging jets - more detailed topological requirements optional - location information for HLT - diagnostics

4 Seas, Sep C.-E. Wulz15 Level-1 Calorimeter Trigger Goals Identify electron / photon candidates Identify jet /  -jet candidates Measure transverse energies (objects, sums, missing E T ) Measure location Provide MIP/isolation information to muon trigger

4 Seas, Sep C.-E. Wulz16 Local / Regional Electron/Photon Trigger Trigger primitive generator (local) Flag max of 4 combinations (“Fine Grain Bit”) Hit +max of > E T threshold Regional calorimeter trigger E T cut Longitundinal cut hadr./electromagn. E T / < 0.05 Hadronic and electromagnetic isolation < 2 GeV One of < 1 GeV One of < 1 GeV Electron / photon   Jet e/ 

4 Seas, Sep C.-E. Wulz17 Typical e/  Level-1 Rates and Efficiencies Single isolated e/  rate at 25 GeV threshold: 1.9 kHz 95% efficiency at 31 GeV

4 Seas, Sep C.-E. Wulz18 Jet /  Trigger {  Jet E T is obtained from energy sum of 3 x 3 regions - sliding window technique, seamless coverage up to |  | < 5  Up to |  | < 3 (HCAL barrel and endcap) the regions are 4 x 4 trigger towers Narrow jets are tagged as  -jets in tracker acceptance (|  | < 2.5) if E T deposit matches any of these patterns

4 Seas, Sep C.-E. Wulz19 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  -jet rate at 80 GeV threshold: 6.1 kHz C.-E. Wulz16Split, Oct. 2002

4 Seas, Sep C.-E. Wulz20 H T Trigger H T, which is the sum of scalar E T of all high E T objects in the event is more useful than total scalar E T for the discovery or study of heavy particles (SUSY sparticles, top): Total scalar E T integrates too much noise and is not easily calibrated –At Level-1 tower-by-tower E T calibration is not available However, jet calibration is available as f(E T, ,  ) Implemented in Global Calorimeter Trigger Rate with cutoff at 400 GeV: 0.7 kHz, 95% efficiency at 470 GeV

4 Seas, Sep C.-E. Wulz21 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.

4 Seas, Sep C.-E. Wulz22 Cathode Strip Chambers Local Muon Trigger 6 hit strips form track segment Vector of 4 hit cells Correlator combines vectors to track segment Comparators allow resolution of 1/2 strip width Superlayer Station Drift Tube Chambers

4 Seas, Sep C.-E. Wulz23 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 p T 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

4 Seas, Sep C.-E. Wulz24 Regional DT/CSC Muon Trigger (Track Finder) Drift Tube Trigger (CSC Trigger similar) Track Segment and direction of extrapolation Bending plane Longitudinal plane

4 Seas, Sep C.-E. Wulz25 Regional RPC Muon Trigger RPC-Trigger is based on strip hits matched to precalculated patterns according to p T and charge. 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. 4/4 3/4 High p T Low p T 3/4 4/4

4 Seas, Sep C.-E. Wulz26 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

4 Seas, Sep C.-E. Wulz27 |  | < 2.1 Trigger rates in kHz L1 Single & Di-Muon Trigger Rates 20, 5;5  W =82.3 %  Z =99.7 %  Bs  =15.1 % 25, 4;4  W =74.2 %  Z =99.5 %  Bs  =18.4 % 14, -;-  W =89.6 %  Z =99.8 %  Bs  =27.1 % L = cm -2 s - 1 L = 2x10 33 cm -2 s -1 working points compatible with current L1 p T binning 18, 8;8  W =84.9 %  Z =99.7 %  Bs  = 7.2 %

4 Seas, Sep C.-E. Wulz28 Global/Central Trigger within ATLAS and CMS 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. Algorithm bits Algorithm bits

4 Seas, Sep C.-E. Wulz29 Global Trigger trigger decision 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/photonsE T, ,  Best 4 non-isolated electrons/photonsE T, ,  Best 4 jets in forward regionsE T, ,  Best 4 jets in central regionE T, ,  Best 4  -JetsE T, ,  Total E T  E T Total E T of all good jetsH T Missing E T E T missing,  (E T missing ) 12 jet multiplicities N jets (different E T thresholds and  -regions) Best 4 muonsp T, charge, , , quality, MIP, isolation Thresholds (p T, E T, N Jets ) Optional topological and other conditions (geometry, isolation, charge, quality)

4 Seas, Sep C.-E. Wulz30 Algorithm Logic in Global Trigger Logical Combinations Object Conditions 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.

4 Seas, Sep C.-E. Wulz31 B s ->  : Example of Topological Trigger  similar. Can ask for opposite charges in addition.  - distributions

4 Seas, Sep C.-E. Wulz32 B s ->  : Example of Topological Trigger Topological conditions:  < 1.5,  < 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).

4 Seas, Sep C.-E. Wulz33 High Level Trigger Goals Validate Level-1 decisionValidate Level-1 decision Refine E T /p T thresholds Refine E T /p T thresholds Refine measurement of position and other parameters Refine measurement of position and other parameters Reject backgrounds Reject backgrounds Perform first physics selection Perform first physics selection Detailed algorithms: see talks of A. Nikitenko (e/ ,jets), N. Neumeister (  ) and other talks related to CMS physics and wait for DAQ/HLT TDR due Dec

4 Seas, Sep C.-E. Wulz34 High Level Trigger Challenges Rate reduction Design input rate: 100 kHz (50 kHz at startup with luminosity 2x10 33 cm -2 s -1 ), i.e. 1 event every 10  s. 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) -  -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.

4 Seas, Sep C.-E. Wulz35 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.

4 Seas, Sep C.-E. Wulz36 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

4 Seas, Sep C.-E. Wulz37 Acknowledgments - my colleagues in CMS and at HEPHY Vienna, especially P. Chumney, J. Erö, S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, J. Erö, S. Dasu, N. Neumeister, H. Sakulin, W. Smith, G. Wrochna, A. Taurok. A. Taurok. - to the Organizing Committee of LHC Days in Split for the invitation and the enjoyable conference. the enjoyable conference.