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The Muon Trigger in ATLAS

The Muon Trigger in ATLAS. Giovanni Siragusa On behalf of the ATLAS Muon Trigger group. Outline. The LHC and Trigger system requirements The ATLAS detector: The Muon Spectrometer The Trigger System Muon Trigger System architecture and performance: Level 1 Level 2 Event Filter

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The Muon Trigger in ATLAS

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  1. The Muon Trigger in ATLAS Giovanni Siragusa On behalf of the ATLAS Muon Trigger group

  2. Outline • The LHC and Trigger system requirements • The ATLAS detector: • The Muon Spectrometer • The Trigger System • Muon Trigger System architecture and performance: • Level 1 • Level 2 • Event Filter • Trigger Commissioning • Conclusions Giovanni Siragusa - ACAT 2007

  3. LHC • Center of Mass Energy: • 14 TeV (p-p) • Design Luminosity: • L = 1034 cm-2s-1 • Integrated Luminosity per year (@ 1034) •  Ldt  100 fb-1 • The cross sections of interesting physics processes are highly suppressed w.r.t. stot • Calibrations and precision physics • Leptonic W decay • New Physics • Higgs boson production Trigger with high selection efficiency 10-6 10-9 • Event rate at LHC (@ design lumi) is ~1 GHz • 40 MHz (BC frequency) x 23 interactions per BC • Maximum allowed acquisition rate is ~200 Hz • Bandwidth ~ 300 MByte/s • Event Size ~ 1.5 MByte Trigger with high rejection capability Giovanni Siragusa - ACAT 2007

  4. The ATLAS detector Design • Inner Detector: • Silicon detectors: pixel, micro-strips • TRT • Thin superconducting magnet with a solenoidal field of 2T • Electro Magnetic Calorimeter • Sampling Pb - Argon (liquid @ 80K) • Hadronic Calorimeter • Scintillation tiles • Muon Spectrometer (MS) • Toroidal magnetic field in air (bending in the z-f plane) • High resolution (e.g. ~50 mm sagitta) • General purpose detector • Capability to observe a wide range of Physics processes • Study of the Physics of the Standard Model and beyond it • SUSY, Extra Dimensions • Any exotic scenario of new Physics at TeV energy scale • First collisions for physics in 2008 • Now commissioning detector and trigger with cosmic rays Physics Giovanni Siragusa - ACAT 2007

  5. Design resolution on the sagitta measurement: 50 mm 10% of relative resolution for muons with pT ~ 1 TeV The ATLAS Muon Spectrometer • High-pT muonsare an important signature for many known (and predicted) processes at TeV energy scale • Low-pT muonsare the major source of Level1 trigger rate • Inhomogeneous toroidal magnetic field in air • Max field 4T • Multiple scattering suppression • Precise measurements of high pT muons • Identification of low pT muons RPC CSC MDT TGC Muons loose in the calorimetric system ~3GeV Muons with pT above 3 GeV arrive at the MS Giovanni Siragusa - ACAT 2007

  6. ~100 kHz 2.5 ms ~2 kHz 10 ms ~200 Hz 2 s The ATLAS Trigger system • Level 1(hardware) • Coarse granularity data from CALO and MUON detectors • Selects Regions Of Interest (ROI) in the detector Reduced bandwidth at Level 2 input • Level 2 (software) • Algorithms optimized for fast rejection • It accesses full granularity data, only inside ROIs Full event access • Event Filter (software) • Uses the Offline algorithms • It can access data from the entire event (after the Event builder) • Seeding strategy Giovanni Siragusa - ACAT 2007

  7. TrigMoore mFast TrigDiMuon mComb mComb mIsol mTile B Physics processor The ATLAS Muon Trigger Level 1 Simulation capability to run on the HLT farms to optimize the hardware selection H i g h L e v e l T r i g g e r Level 2 Selection EF Selection 2 s latency time 10 ms latency time 2.5 ms latency time High-pT physics MOORE MS Low-pT physics RPC CTP mCTPI CALO MuId SA TGC ID MuId COMB Giovanni Siragusa - ACAT 2007

  8. Level 1 selection • The selection is based on the definition of allowed geometrical roads, the Coincidence Windows, whose center is defined by the infinite momentum track • The width of the road defines a pT threshold • Three pT thresholds can be applied for a Level 1 configuration • 6, 8, 10 GeV (Low-pT) • 11, 20, 40 GeV (High-pT) The Coincidence Window is implemented with FPGA Can be reconfiguredtooptimize the algorithm for different running conditions Giovanni Siragusa - ACAT 2007

  9. Barrel Low pT OK, NO High pT  NO Trigger 3-station coincidence trigger efficiency of TGC 6 GeV 20 GeV Endcap  Level 1: Acceptance Level 1 simulation results single muons, pT 100 GeV • Level 1 barrel acceptance: • 83% Low-pT • 79% High-pT ~30% of barrel inefficiencies are due to feet and elevator sectors Giovanni Siragusa - ACAT 2007

  10. High-pT thresholds Low-pT thresholds • 6 GeV • 8 GeV • 10 GeV • 11 GeV • 20 GeV • 40 GeV Endcap 0.8 6 GeV 20 GeV 0.4 Level 1: Efficiency curves Barrel Level 1 simulation • The value at the plateau is due to the acceptance • The sharpness of the ramp-up is a function of the resolution • The efficiency above the threshold is due to fake tracks  impact on the trigger rates pT Giovanni Siragusa - ACAT 2007

  11. Expected single muon trigger rates at a luminosity of 1033 cm-2s-1 Rate [Hz] Barrel only • 6 GeV • 8 GeV • 10 GeV threshold [GeV] The cosmic configuration is showed as an effective threshold of 3 GeV Level 1 efficiency Level 1: Rates Inclusive μcross-section @ LHC (prompt μ and /K decay) Level 1 simulation Giovanni Siragusa - ACAT 2007

  12. Level 2 mFast mComb Confirm the Level-1 trigger with a more precise pT estimation within a “Region of interest (RoI)” Contribute to the global Level-2 decision. “Global Pattern Recognition” involving trigger chambers and positions of MDT tubes (no use of drift time) “Track fit” involving drift time measurements, performed for each MDT chamber Fast “pT estimate” via a Look-up-table (LUT) with no use of time consuming fit methods • Refine the Fast pT using ID data • more sharpness @ 6 GeV threshold • Identify the muon track in ID to ease the search for secondary muon tracks. • High reduction on the /K was obtained thanks to the pT match mIsol uses calorimetric information to select isolated muons from W and Z decays mTileidentifies low pT muons using the measure of the energy loss in the calorimeters Efficiencies Giovanni Siragusa - ACAT 2007

  13. Level 2: Resolution Barrel mFast mComb idScan End Cap 50 GeV 10 GeV 5 GeV Giovanni Siragusa - ACAT 2007

  14. MooAlgs MooMakeRoads MooMakeTracks … MooStatistics MooEvent TrigMoore MooHLTAlg MuonIdentification Moore TriggerAlgorithms Event Filter Offline • The Muon Event Filter (TrigMoore) • uses the same Algorithms as the Offline. • The Feature Extraction Algorithms (FEX) calculate the muon track parameters • Operating configurations: • Seeded from Level 2 (Standard) • Seeded from Level1 (Trigger studies) • Unseeded (Full Event Reconstruction) • The Trigger Decision operates via the insertion (in any point of the trigger chain) of the Hypothesis Algorithms (Hypo) Hypo and FEX define a trigger sequence Events are selected if they satisfy an item in the trigger menu Giovanni Siragusa - ACAT 2007

  15. TrigMoore Seeding Algs • MOORE • Reconstruction of the tracks in the Muon Spectrometer (MS) • Muid Stand Alone • Propagation of the tracks to the Impact Point (using calorimetric measurement) • Good pT resolution (less than 10% at 1 TeV) • Muid Combined • Combines the MS tracks with Inner Detector (ID) tracks • Refines pT resolution • ID improves resolution at low pT (less than 50 GeV) • MS improves resolution at high pT Moore Algs Hypo MuIdStandAlone Algs CALO Hypo MuIdCombined Algs ID Hypo Giovanni Siragusa - ACAT 2007

  16. Single muons pT resolutions |h| < 2.5 5 50 100 TrigMoore: Resolution • The low amount of material in the Muon Spectrometer reduces the multiple scattering • The resolution performances are highly related to the chambers alignment • Single muons pT resolution is under 4% • (for pT < 100 GeV) Giovanni Siragusa - ACAT 2007

  17. 40 GeV muons selection efficiency h 40 GeV muons selection efficiency f TrigMoore: Efficiency Efficiency is defined with respect to the seeding level Here the efficiency is referred to Level 2 (standard configuration) High efficiency (95%) for muons up to 1 TeV transverse momentum Barrel – End Cap transition Inefficiencies in the feet region Giovanni Siragusa - ACAT 2007

  18. Barrel mu(6) 3.0 kHz mu(20) 25 Hz End-Cap mu(6) 3.1 kHz mu(20) 27 Hz Total (@ 1033 cm-2s-1): mu(6) 6.1 kHzmu(20) 52 Hz EF: Rates 1033 cm-2s-1 Barrel only At low pT the single muon rate is dominated by p/K decays in flight Giovanni Siragusa - ACAT 2007

  19. 10-1 Background from neutral and charged 10-2 10-3 Counting rates (kHz/cm2) L=1034cm-2s-1 Fake track prob. on single muon events Fake track prob. on single muon, SF=x5 Inner Station Middle Station x10 Outer Station x5 x2 no Cavern background • The p-p collisions generate a radiation that interacts with the detector’s and accelerator’s materials • As a consequence neutral and charged particles are released • (photons and neutrons) • particles diffuse like a gas in the cavern, giving rise to time uncorrelated hits (fake tracks) • This effect increases linearly with luminosity • Safety Factor (SF) = a factor that multiplies nominal background – it takes care of possible underestimations of the background Geant4 Geant3 No pT threshold applied ! Giovanni Siragusa - ACAT 2007

  20. Trigger on complex events Crack • The muon trigger selection has been performed on complex events (top events are shown) • Realistic simulation of trigger is included in Physics Analysis • Started the Monitoring and Data Quality activity to be ready for real data taking Feet region Muons absorbed in Calorimeters Giovanni Siragusa - ACAT 2007

  21. Misaligned Geometry misal-misal nominal-nominal • Blue = MOORE • Red = MuidSA • Magenta= MuidCB • Comparison of the resolutions of the EF algorithms for nominal and “real” geometry (material distortions, inhomogeneous magnetic field) • The Computing System Commissioning will be based on simulated data that will reproduce in the maximum detail real data h h misal-nominal h Giovanni Siragusa - ACAT 2007

  22. UX15 Sector 13 Level 2 – RPC only y Reconstructed Muon Eta Reconstructed Muon Phi x First Cosmic Run Trigger Commissioning: Run in February 2007 with cosmics data • Trigger (Level 1 + HLT) run Online Unfortunately MDT chambers off. Tested HLT workflow and architecture • RPC Chambers of Sector 13 provided cosmic-ray trigger signal • Full hardware Central Trigger Processing chain in place • Full hardware and software for Level 2 handling (processors, readout links, HLT sw suite) • Version of the Level 2 algorithm optimized for cosmic rays identification has been successfully running and triggering • Level 1 cosmic setting: • opening the concidence windows as much as possible • minimum Level1 threshold value is limited by RPC cabling Level 1 simulation Giovanni Siragusa - ACAT 2007

  23. Conclusions • Next year we will have first collisions at LHC • First test on cosmic data have been performed and all the systems are extensively checked and tested • All the studies on the muon trigger indicate that the major requirements are satisfied • Optimization of the trigger chain will be possible in the first stages of LHC operation (low luminosity) • The ATLAS trigger system will be ready for Physics and data taking Giovanni Siragusa - ACAT 2007

  24. Backup Giovanni Siragusa - ACAT 2007

  25. LVL1 barrel: Cosmic setting Cosmic setting is obtained by opening the concidence windows as much as possible, minimum lvl1 threshold value is limited by RPC connectivity. It have been used for Sector 13 data taking and for the future trigger commissioning Level 1 simulation pT [GeV] Giovanni Siragusa - ACAT 2007

  26. LVL1 barrel : Low-pT Trigger rates Using the Level-1 Efficiency curves we may estimate the rates with different threshold. Level 1 simulation Giovanni Siragusa - ACAT 2007

  27. Level 1 barrel :High-pT Trigger rates Preliminary Level 1 simulation Giovanni Siragusa - ACAT 2007

  28. Level 1 endcap: Rates Level 1 simulation Giovanni Siragusa - ACAT 2007

  29. Level 2: Efficiency Low - pT High - pT The Efficiency is shown for FEX algorithm and after the HYPOTHESIS algorithm cut Hypo off Hypo on Giovanni Siragusa - ACAT 2007

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