Sez. di Lecce Universita` degli Studi del Salento The Muon Trigger in ATLAS Giovanni Siragusa On behalf of the ATLAS Muon Trigger group

2007 April 24Giovanni Siragusa - ACAT 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

2007 April 24Giovanni Siragusa - ACAT LHC Center of Mass Energy: –14 TeV (p-p) Design Luminosity: –L = cm -2 s -1 Integrated Luminosity per year ) –  Ldt  100 fb -1 The cross sections of interesting physics processes are highly suppressed w.r.t.  tot –Calibrations and precision physics Leptonic W decay –New Physics Higgs boson production 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 Trigger with high selection efficiency

2007 April 24Giovanni Siragusa - ACAT The ATLAS detector 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 Inner Detector: –Silicon detectors: pixel, micro- strips –TRT –Thin superconducting magnet with a solenoidal field of 2T Electro Magnetic Calorimeter –Sampling Pb - Argon 80K) Hadronic Calorimeter –Scintillation tiles Muon Spectrometer (MS) –Toroidal magnetic field in air (bending in the z-  plane  –High resolution (e.g. ~50  m sagitta) Physics Design

2007 April 24Giovanni Siragusa - ACAT The ATLAS Muon Spectrometer CSC RPC TGC MDT Design resolution on the sagitta measurement: 50  m 10% of relative resolution for muons with p T ~ 1 TeV High-p T muons are an important signature for many known (and predicted) processes at TeV energy scale Low-p T muons are the major source of Level1 trigger rate Muons loose in the calorimetric system ~3GeV Muons with p T above 3 GeV arrive at the MS 1.Precise measurements of high pT muons 2.Identification of low pT muons Inhomogeneous toroidal magnetic field in air 1.Max field 4T 2.Multiple scattering suppression

2007 April 24Giovanni Siragusa - ACAT ~100 kHz ~2 kHz ~200 Hz 2.5  s 10 ms 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 Level 2 (software) Algorithms optimized for fast rejection It accesses full granularity data, only inside ROIs Event Filter (software) Uses the Offline algorithms It can access data from the entire event (after the Event builder) Seeding strategy Reduced bandwidth at Level 2 input Full event access

2007 April 24Giovanni Siragusa - ACAT The ATLAS Muon Trigger  Fast B Physics processor  Tile  Comb TrigDiMuon  Isol  Comb 10 ms latency time TrigMoore MOORE 2 s latency time Level 1 Simulation capability to run on the HLT farms to optimize the hardware selection Level 2 Selection EF Selection RPC TGC  CTPI CTP 2.5  s latency time MuId SA MuId COMB MS CALO ID H i g h L e v e l T r i g g e r High-p T physics Low-p T physics

2007 April 24Giovanni Siragusa - ACAT 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 p T threshold Three p T thresholds can be applied for a Level 1 configuration 6, 8, 10 GeV (Low-p T ) 11, 20, 40 GeV (High-p T ) The Coincidence Window is implemented with FPGA Can be reconfigured to optimize the algorithm for different running conditions

2007 April 24Giovanni Siragusa - ACAT Level 1: Acceptance ~ 30% of barrel inefficiencies are due to feet and elevator sectors 3-station coincidence trigger efficiency of TGC Endcap 6 GeV 20 GeV Level 1 barrel acceptance: 83% Low-p T83% Low-p T 79% High-p T79% High-p T Level 1 simulation results   Barrel Low p T OK, NO High p T NO Trigger single muons, p T 100 GeV

2007 April 24Giovanni Siragusa - ACAT pTpT Level 1: Efficiency curves 1.The value at the plateau is due to the acceptance 2.The sharpness of the ramp-up is a function of the resolution 3.The efficiency above the threshold is due to fake tracks  impact on the trigger rates 6 GeV 8 GeV 10 GeV Low-p T thresholds 11 GeV 20 GeV 40 GeV High-p T thresholds Level 1 simulation 6 GeV 20 GeV Endcap Barrel

2007 April 24Giovanni Siragusa - ACAT Level 1: Rates Inclusive μ cross- LHC (prompt μ and  /K decay) 6 GeV 8 GeV 10 GeV Level 1 efficiency Level 1 simulation threshold [GeV] Rate [Hz] Expected single muon trigger rates at a luminosity of cm -2 s -1 The cosmic configuration is showed as an effective threshold of 3 GeV Barrel only

2007 April 24Giovanni Siragusa - ACAT  Fast Confirm the Level-1 trigger with a more precise p T 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 “p T estimate” via a Look-up-table (LUT) with no use of time consuming fit methods Refine the  Fast p T using ID data –more 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 p T match  Comb Level 2  Isol uses calorimetric information to select isolated muons from W and Z decays  Tile identifies low p T muons using the measure of the energy loss in the calorimeters Threshold  Fast - Hypo  Comb - Hypo Low-p T (6 GeV) 99.5 – 98.5 (10 GeV single  ) 96.3 – 96.1 (10 GeV single  ) High-p T (20 GeV) 99.6 – 96.7 (50 GeV single  ) 95.0 – 94.8 (50 GeV single  ) Efficiencies

2007 April 24Giovanni Siragusa - ACAT Level 2: Resolution Barrel End Cap  Fast  Comb idScan 50 GeV 10 GeV5 GeV

2007 April 24Giovanni Siragusa - ACAT Event Filter 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) MooAlgs MooMakeRoads MooMakeTracks … MooStatistics MooEvent TrigMoore MooHLTAlg MuonIdentification Hypo and FEX define a trigger sequence Events are selected if they satisfy an item in the trigger menu Offline

2007 April 24Giovanni Siragusa - ACAT TrigMoore 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 p T resolution (less than 10% at 1 TeV) Muid Combined –Combines the MS tracks with Inner Detector (ID) tracks –Refines p T resolution ID improves resolution at low p T (less than 50 GeV) MS improves resolution at high p T Moore Algs MuIdStandAloneAlgs Seeding Algs MuIdCombinedAlgs Hypo Hypo Hypo CALO ID

2007 April 24Giovanni Siragusa - ACAT  < 2.5 p T resolutions Single muons 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 p T resolution is under 4% (for p T < 100 GeV)

2007 April 24Giovanni Siragusa - ACAT Inefficiencies in the feet region 40 GeV muons selection efficiency   Barrel – End Cap transition 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

2007 April 24Giovanni Siragusa - ACAT EF: Rates cm -2 s -1 At low p T the single muon rate is dominated by  /K decays in flight Muon sources 6 GeV/c threshold kHz  /K 1.9 B0.67 C0.34 W0.003 Tnegligible Total 3.0 kHz Barrel mu(6) 3.0 kHz mu(20) 25 Hz End-Cap mu(6) 3.1 kHz mu(20) 27 Hz Total cm -2 s -1 ): mu(6) 6.1 kHz mu(20) 52 Hz Barrel only

2007 April 24Giovanni Siragusa - ACAT 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 Counting rates (kHz/cm 2 ) Background from neutral and charged L =10 34 cm -2 s -1 Outer Station Inner Station Middle Station Fake track prob. on single muon, SF=x5 Fake track prob. on single muon events x10 x5 x2 no No p T threshold applied ! Geant3 Geant4

2007 April 24Giovanni Siragusa - ACAT Trigger on complex events 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 Muons absorbed in Calorimeters Feet region Crack

2007 April 24Giovanni Siragusa - ACAT Misaligned Geometry 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 nominal-nominal misal-misal Blue = MOORE Red = MuidSA Magenta= MuidCB    misal-nominal

2007 April 24Giovanni Siragusa - ACAT 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 First Cosmic Run Efficiency (plateau) p 90% 83.3%3.5 GeV x y Sector 13 UX15 Reconstructed Muon Eta Reconstructed Muon Phi Level 2 – RPC only Level 1 cosmic setting: opening the concidence windows as much as possible minimum Level1 threshold value is limited by RPC cabling Level 1 simulation

2007 April 24Giovanni Siragusa - ACAT 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

2007 April 24Giovanni Siragusa - ACAT Backup

2007 April 24Giovanni Siragusa - ACAT LVL1 barrel: Cosmic setting p T [GeV] 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

2007 April 24Giovanni Siragusa - ACAT LVL1 barrel : Low-pT Trigger rates Using the Level-1 Efficiency curves we may estimate the rates with different threshold. Muon sources 10 GeV 10 GeV threshold Lumi= GeV 8 GeV threshold Lumi= GeV 6 GeV threshold Lumi= GeV 5 GeV threshold Lumi=10 33 "Cosmic" "Cosmic" threshold Lumi=10 33  /K 5400 Hz8830 Hz10470 Hz21800 Hz62500 Hz b 920 Hz1160 Hz1650 Hz2220 Hz3360 Hz c 510 Hz660 Hz970 Hz1400 Hz2400 Hz W 3 Hz t Negligible Sum 6.8 kHz11 kHz13 kHz25.5 kHz68.3 kHz Level 1 simulation

2007 April 24Giovanni Siragusa - ACAT Level 1 barrel : High-pT Trigger rates Muon sources 11 GeV 11 GeV threshold Lumi= GeV 20 GeV threshold Lumi=10 34  /K 7420 Hz3540 Hz b 2330 Hz760 Hz c 1100 Hz340 Hz W 28 Hz26 Hz t Negligible Sum 12 kHz4.7 kHz Preliminary Level 1 simulation

2007 April 24Giovanni Siragusa - ACAT Level 1 endcap: Rates Muon Sources 6 GeV threshold Lumi=10 33  /K 5.9 b 1.8 c 1.0 W negligible t Sum 8.7 KHz 20 GeV 20 GeV threshold Lumi= GeV 40 GeV threshold Lumi= negligible 8.9 KHz4.4 KHz Level 1 simulation

2007 April 24Giovanni Siragusa - ACAT Level 2: Efficiency GeV  Fast eff. 6 GeV  Comb eff. 6 GeV  Fast eff. 20 GeV  Comb eff. 20 GeV 598.2%20.5%18.7%0.2% %98.5%96.3%96.1%99.5%3.3%3.2%< 0.1% %98.8%97% 99.6%96.7%95.0%94.8% %98.5%96.7% 99.6%96.5%94.9% %98.1%94.9% 98.8%94.2%92.6% Low - p T High - p T Hypo off Hypo on The Efficiency is shown for FEX algorithm and after the HYPOTHESIS algorithm cut