ATLAS Muon Spectrometer: System Performance & Physics Goals

1. Muon System and Physics Performance Ludovico Pontecorvo CERN-INFN

2. Outlook • The ATLAS muon spectrometer • Physics Goals • Resolution and Acceptance • Signals & Backgrounds • The Magnet systems • The Trigger and Tracking concepts • Experimental results from Test beam Ludovico Pontecorvo – CERN/INFN

3. ATLAS Layout Ludovico Pontecorvo – CERN/INFN

4. End cap: 1 < |h | < 2.7 Tracking with MDTs & CSCs Triggering with TGCs Barrel: |h | < 1.0 Tracking with MDTs Triggering with RPCs The ATLAS Muon Spectrometer Acceptance : |h | < 2.7 Pt Resolution: ~10% @ 1 TeV/c < 3 % Pt<250 GeV/c Ludovico Pontecorvo – CERN/INFN

5. MH= 130 GeV muon spectrometer standalone Standalone measurement better than Inner Detector for MH>180 GeV S.M. Higgs search Muons relevant for Trigger and ID in the full energy range Ludovico Pontecorvo – CERN/INFN

6. 5 discovery curves MSSM Higgs Bosons search mh < 135 GeV mA mH mH at large mA A, H, H cross-section ~ tg2 Best sensitivity from A/H  , H   A/H  , tg  = 38 m~11 GeV bbA/H   : -- covers good part of region not excluded by LEP -- experimentally easier than A/H   -- crucial detector : Muon Spectrometer (high-pT muons from narrow resonance) Relevant for mass and couplings measurement Ludovico Pontecorvo – CERN/INFN

7. Low Pt trigger High Pt trigger Signals and Backgrounds Expected bkg rate Photons and Neutrons are the main source of uncorrelated background Muon rates CSC MDT+TGC MDT+RPC • Single counting rate: • Barrel < 40 Hz/cm2 • End Cap 20-1000 Hz/cm2 Ludovico Pontecorvo – CERN/INFN

8. Multiple scattering The muon spectrometer resolution dominates for Pt > 100 GeV/c Energy loss fluctuations Chamber resol and align. Inner tracker stand alone Muon spectrom. standalone Resolution • Resolution limited by : • M.S. and Energy Loss Fluct. @ 3% for 10 < Pt < 250 GeV/c • Chamber Resolution and Alignment for Pt > 250 GeV/c Ludovico Pontecorvo – CERN/INFN

9. Trigger concept • Trigger algorithm relies on pointing coincidences in two views of two (low Pt) or three (high Pt) units of trigger detectors • Trigger detectors must have very good timing properties to allow bunch crossing ID • Low Pt trigger Thr @ 6 GeV/c • High Pt trigger Thr @ 20 GeV/c • Trigger Coverage |h | < 2.4 Ludovico Pontecorvo – CERN/INFN

10. Barrel Trigger rate (Hz) 104 103 Luminosity Barrel 104 Trigger rate (Hz) 103 102 Luminosity Trigger efficiency and rates Muon trigger rate @ 1033 cm-2 s-1 : Low Pt (> 6 GeV/c) 10 KHz High Pt (> 20 GeV/c) 200 Hz Pt Gev/c Good safety margin over accidental trigger rate Ludovico Pontecorvo – CERN/INFN

11. The Magnet systems BT Parameters : 25.3 m length 20.1 m outer diameter 8 coils 1.08 GJ stored energy 370 tons cold mass 830 tons weight 4 T on superconductor 56 km Al/NbTi/Cu conductor 20.5 kA nominal current 4.7 K working point 8 separate coils Ludovico Pontecorvo – CERN/INFN

12. Conductor double Pancake: 14 out of 16 ready Cryostat vacuum vessel: 5 out of 8 delivered Barrel toroid status The completion of these components is expected by May 2003 Ludovico Pontecorvo – CERN/INFN

13. Vacuum vessels delivered at CERN Services Turret Magnet Coils (4.5K) Thermal Radiation Shield (80K) Vacuum Vessel (300K) End Cap Toroids Pancake windings: 8 of 16 done Ludovico Pontecorvo – CERN/INFN

14. Field Integral vs h Y (cm) Need to measure accurately the coordinate in the non bending plane Field integral inhomogeneous in the tracking volume RPC and TGC Need to take into account the differences in Lorentz angle for the calibration of the precision chambers More than a single RT relation per wire X (cm) Field Maps Ludovico Pontecorvo – CERN/INFN

15. Read-out electronics 8 chs Ga-AS 3 stage ampli.+discrim Gas Volume + spacers Operating Conditions (Egas~ 5 KV/mm) Gas: C2H2F4 96.7% - C4H10 3% - SF6 0.3% ; bakelite ~ 2x1010 cm ; Gas Gap d = 2 mm ; Graphite coated HV electrodes Cu read out strips 30 mm pitch Time resolution ~1.5 ns Bakelite Plates Read out strips X readout strips Foam Gas HV Grounded planes Y readout strips PET spacers Graphite electrodes Barrel Trigger chambers: RPC Ludovico Pontecorvo – CERN/INFN

16. RPC Cosmic Test Station Test rate: 8 chambers/week • Plateau efficiency • V-I curve • Noise • Muon radiography RPC Muon Radiography: Innefficiency only close to spacer positions Time Tests on Production chambers Ludovico Pontecorvo – CERN/INFN

17. Integrated charge 30 15 mC/10 Days 25 Total charge (mC/cm2) time • Aim to integrate 300 mC/cm2  10 Atlas Years with safety factor > 5 • Measurement still ongoing • Previous tests on RPC prototype showed good efficiency and time resolution after 8 ATLAS years RPC Ageing test 3 production RPCs currently ageing at the CERN Gamma Irradiation Facility Ludovico Pontecorvo – CERN/INFN

18. MWPC with small cathode-cathode distance: Anode pitch: 1.8 mm Anode-Cathode dist: 1.4 mm Cathode-Cathode dist: 2.8 mm Operating conditions Gas : 55 % CO2 , 45 % N-Pentane HV: 3.1 KV Saturated avalanche mode Very short drift time due to the thin gapensures the good time resolution needed for Bunch Crossing ID Wire signal used to provide the trigger, strip signals used for the second coordinate END CAP Trigger Chambers: TGCs Ludovico Pontecorvo – CERN/INFN

19. Efficiency with source off hit time distrib. % hits in window 100 % 25 ns Efficiency at ~ 1 kHz/cm2 20 40 60 20 40 60 Time (ns) Time (ns) Results from high rate test Ludovico Pontecorvo – CERN/INFN

20. ~ 1 kHz/cm2 Trigger Efficiency under irradiation Ludovico Pontecorvo – CERN/INFN

21. 4 planes per chamber Precision chambers: CSC MWPC with symmetric cell where anode-cathode distance is equal to the anode wire pitch Anode pitch: 2.54 mm Cathode read-out pitch: 5.08 mm Very good spatial resolution: 50 mm per plane reading charge on the cathode strips Good time resolution: 7 ns Due to small drift time (30 ns) Ludovico Pontecorvo – CERN/INFN

22. High Rate 2.3 KHz/cm2 69 mm Low Rate 0.1 KHz/cm2 • Distributions of residuals: • Reconstructed CSC track position - Silicon Telescope extrapolation • Tails mainly due to d-electrons at low rate, and to overlapping signals at high rate. 47 mm Results from high rate test The expected background rate at h=2.7 is 2.7 KHz/cm2 (with safety factor 5) The CSC System can provide very good space resolution Resolution vs Rate Inefficiency vs Rate Inefficiency= distance from track > 300 mm Ludovico Pontecorvo – CERN/INFN

23. Reconstructed track Precision Chambers: MDTs Operating Conditions Gas Mixture: 93 % Ar 7% CO2 Absolute pressure: 3 Bar HV: 3080 V Gas Gain: 2x104 Threshold: 25 electrons Drift tubes mechanical parameters: Tube Radius : 15 mm Tube thickness 400 mm Wire diameter. 50 mm Tube length: 1-6 mt Chamber mech. Precision 20 mm Ludovico Pontecorvo – CERN/INFN

24. Space charge effect on the single tube resolution Resolution (mm) Space charge fluctuations at high irradiation worsen the resolution far away from the wire Radius mm Resolution • Single tube resolution • Precise knowledge of space-time calibration (RT-Rel) • Alignment Muon Spectrometer resolution @ High Pt depends crucially on Single station space resolution (6-8 meas.) Low Rate 40-60 mm High Rate 40-90 mm Ludovico Pontecorvo – CERN/INFN

25. RT relation known at the level of 25 mm over almost all the drift distance True RT - calibration (mm) +25 mm -25 mm The RT-relation close to the wire is distorted by Threshold effects Drift time (ns) RT-Relation Ludovico Pontecorvo – CERN/INFN

26. Station 3 Station 2 Axial lines (RASNIK) Projective lines (RASNIK) Station 1 • Projective Lines to monitor relative movements of stations • Axial lines to monitor chambers movement within a station Barrel Alignment • The relative chamber • positions should be known with ~30mmprecision to ensure high Pt resolution • alignment system based on optical elements (RASNIK) to reconstruct and monitor the geometry of the spectrometer with the required accuracy Ludovico Pontecorvo – CERN/INFN

27. Magnet on Virtual IP End Cap Stand BML on rail 2 BML on rails BIL on rail Projective platform Survey platforms Barrel Stand 2002: Barrel & End Cap System Test • Test the barrel and end-cap alignment concepts • Test system and chamber performances with a barrel and end cap sector (6+6 chambers) End Cap Sector Barrel Sector Ludovico Pontecorvo – CERN/INFN

28. Residual difference between chamber position using tracks and alignment system 2.0 Residuals mm 60 RMS = 15 mm 1.5 Displacements from track reconstruction (mm) 40 1.0 20 0 -20 0.5 -40 0.5 1.0 1.5 2.0 -60 0.5 1.0 1.5 2 Displacement from alignment system (mm) Position (mm) • Displace one chamber from middle station, along supporting rail • Check alignment reconstructed position against track reconstructed position The 15 mm RMS of the residuals distribution proves the correctness of the alignment system concept Alignment test result Ludovico Pontecorvo – CERN/INFN

29. The ATLAS Muon Spectrometer will provide powerful muon trigger and identification over the full energy range with a large angular acceptance • The very good momentum resolution will ensure high quality stand alone measurement for most of the physics channels • under study (H->4m, A->mm, Z’->mm) • What’s Next? • System Test with Tracking and Trigger chambers • Trigger System Test Conclusions Construction and Tests: • The Magnet systems are well advanced in the construction • Trigger and Precision chambers are under construction • The chambers performance at high rate is adequate to the LHC environment • The alignment concept is validated by the results from the 2002 System Test of a full sector of barrel and end-cap precision chambers Ludovico Pontecorvo – CERN/INFN