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The ATLAS RPC Level-1 Muon Trigger: Design and Simulation

The ATLAS RPC Level-1 Muon Trigger: Design and Simulation. Francesco Conventi University of Naples and INFN Naples on behalf of Naples and ROMA1 Level-1 Trigger group. VII th Workshop on Resistive Plate Chambers and Related Detectors. LHC machine and ATLAS detector Physics @ LHC

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The ATLAS RPC Level-1 Muon Trigger: Design and Simulation

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  1. The ATLAS RPC Level-1 Muon Trigger: Design and Simulation Francesco Conventi University of Naples and INFN Naples on behalf of Naples and ROMA1 Level-1 Trigger group VIIth Workshop on Resistive Plate Chambers and Related Detectors

  2. LHC machine and ATLAS detector • Physics @ LHC • Muon Spectrometer • Trigger/DAQ in ATLAS • Trigger chambers: RPC • Level -1 RPC Trigger Logic and segmentation Overview • LHC and ATLAS detector • Level-1 Muon Trigger • Level-1 Simulation • Detector description • Coincidence Windows • Physics performances

  3. Muon Spectrometer Hadronic calorimeter EM calorimeter Inner Detector ATLAS experiment @ LHC ATLAS detector

  4. The ATLAS physics program • The high energy and luminosity of the LHC offers a large range of physics opportunities: • Higgs boson searches (113.5 GeV/c < mH < 1 TeV/c) • SUSY • Precision measurements (W and t quark) • B physics For mH > 130 GeV/c the best experimental signature come from the H  4 μdecay mode SM Higgs branching fractions

  5. The ATLAS Muon Spectrometer view Barrel: | η | < 1.1 Tracking with MDTs Triggering with RPCs End cap: 1 < | η | < 2.7 Tracking with MDTs & CSCs Triggering with TGCs view Acceptance : |h | < 2.7 pT Resolution: ~10% pT1 TeV/c < 3 % pT < 250 GeV/c 3 stations of RPCs!

  6. Y (cm) X (cm) MDT RPC The ATLAS Muon Spectrometer The Magnet systems 8 separate coils Huge dimension: 20 m in diameter, 25 m in length Toroidal configuration in the Barrel region: Tracks deflelcting mainly in the  side. Moore H4 μ(MH= 130 GeV/c) Muon Spectrometer standalone Deflection depends on the pT value! view MH(reconstructed)=129.5 GeV/c σ= 3.1 GeV/c

  7. Bakelite Plates Grounded planes  readout strips PET spacers Foam Layer2 Graphite electrodes Layer1 The triggering chambers: RPC readout strips Each ATLAS Units is composed by two independent RPC layer!! HV Gas More than 1000 RPCs will be installed in the BARREL region for a total of coverage of 3650 m2 2  readout strips The ATLAS RPCs Units: • ATLAS RPC Requirements: • High efficiency and time resolution (1 ns) • High rate capability (100 Hz/cm2) • Resolution of 5-10 mm in the  projection (2nd coordinate measurements) • Gas mixture: • C2H2F4 94.7% - C4H10 5% - SF6 0.3% • Working in Avalanche Mode • Readout strips: • 2 orthogonal readout strips allowing the measurements of  and  coordinate 2  readout strips

  8. RPC Efficiency ATLAS RPC: Production and Test status* 98% of tested units have Efficiency > 97% • 2% of Efficiency is lost because of the PET spacers and border effects Naples Cosmic rays Test Station Preliminary Test Results on 250 RPCs Plateau @ 10 kV (Naples conditions) *for details see P. Iengo’s presentation @ RPC 2003

  9. The ATLAS Trigger/DAQ scheme Interaction rate (1 GHz) The Level 1 Logic Level-1 Trigger • output: 100 KHz • All data • Region Of Interest • Rejection factor ~102 • Latency ~10 ms Level-2 Trigger • output: 1 KHz • Events reconstruction • Rejection factor ~10 • Latency ~1 s Level-3 Trigger (EF) DAQ (100 Hz) • Data from Calorimeter ⊕ μ Spectrometer • Bunch Crossing Identification • Region of Interest determination • Rejection factor 104 • Latency ~ 2.5 μs

  10. Basic principle (Physics): Selection of events with muons having a large trasverse momentum (pT) (Trigger): Identification of candidate muon tracks coming from the interaction vertex within a pT range. (Algorithm): Demand a coincidence of hits in different RPCs chamber within geometrical road. Level1 Trigger Logic in the Spectrometer Barrel • Level-1 algorithm performed in both  and  projections • 2 pT regimes: • Low-pt ( μ< 10 GeV/c) with RPC1 and RPC2 • High-pt ( μ 20 GeV/c) with RPC2 and RPC3 ⊕ Low-pT

  11. strips strips A trigger sector in the ηprojection A trigger sector 32 Trigger Sectors RPC RPCs located in the MIDDLE and OUTER sectors

  12. Level-1μTrigger segmentation • All the relevant functions needed for the barrel trigger algorithm are performed by the COINCIDENCE MATRIX ASIC (CMA) • About 4000 CMA in the whole barrel Off detector High PtCMA (x4) RPC n.3 High PtPAD (x6/7) Sector Logic MUCTPI RPC n.1 RPC n.2 Low PtPAD (x6/7) Low PtCMA (x4) On detector • The CM A board • Timing and shaping the signals from RPCs • Trigger algorithm (3 pT threshold) • Majority logic • Readout ROI

  13. Projection of a PAD onto the pivot plane A PAD corresponds to 2 eta-CMs and 2 phi-CMs The position of a ROI is given by overlap of an eta-CM with a phi-CM

  14. The Coincidence Matrix Asic (CMA) scheme

  15. Level-1 μ Trigger: Simulation A code with very detailed simulation of the logic of the basic hardware components and of the related readout format run in the ATLAS offline simulation framework (ATHENA). • RPC positions and structure are derived from an ASCII database (AMDB) which includes also detailed informations on inactive volumes (PET spacers, border) • Detector response has been modelled according to the behavior of RPCs measured in laboratory test using GEANT3 package

  16. OK pT>(pT)thr KO pT>(pT)thr pT<(pT)thr pT<(pT)thr OK KO Level-1 simulation: The algorithm • The width of the COINCIDENCE WINDOW depends on: • The pT threshold • η coordinate • Muon Spectrometer layout Associate to each pivot strip a COINCIDENCE WINDOW in the Low-pT and in the High pT system RPC3 High-pT RPC2 RPC2 Pivot RPC1 Low-pT Coincidence window

  17. 6GeV 8GeV 10GeV Level-1 simulation: The coincidence windows |h|=1.05 Coincidence Windows width 1 0 η An automatic procedure is able to determine the ~ 20000 foreseen Coincidence Windows in the Spectrometer

  18. Level-1 simulation: Acceptance ATLAS Support structures Low-pT acceptance: μ hit (at least) 3 out of 4 readout planes (in both η and  projections) High-pTacceptance: Low-pT⊕ (at least) ½ planes in the outer station.

  19. Level-1 simulation: Trigger performances A large sample of single muon events with a wide pT range has been tracked in the simulated detector, processed using the simulation code and applying the predefined Coincidence windows Single muons Trigger Efficiency curves for 90% (nominal) efficiency at threshold

  20. Level-1 Efficiency • Major source in the Low-pT • Great uncertainty on σ Level-1 simulation: Trigger rates Using the Level-1 Efficiency curves we may estimate the rates with different threshold. Low-pT Trigger rates ~ 10 kHz High-pT Trigger rates ~ 1.5 kHz Inclusive μcross-section @ LHC (prompt μand /K decay)

  21. Conclusions • The ATLAS Barrel Level-1 muon trigger is a big and complex system: • Extremely high initial interactions rate (1 GHz) • Large RPCs system (~1000 Units, 3650 m2) • Trigger electronics reduces informations from 350k readout channels to 400 32-bit words • Flexible pT selection system (Low/High pT ) • Events rejection factor 104 • Big efforts from both hardware and software community: • Production, QC and Tests of the RPCs • Developments of very detailed simulation code • Simulation results confirm the design performances of the Level-1 RPC system • Selection efficiency for all the High/Low pT thresholds and trigger rates

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