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

3. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 2 Outlook The ATLAS muon spectrometer  The ATLAS muon spectrometer  Physics Goals  Resolution and Acceptance  Signals & Backgrounds  The Magnet systems  The Trigger and Tracking concepts  Experimental results from Test beam

4. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 3 ATLAS Layout

5. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 4 The ATLAS Muon Spectrometer Acceptance : |  | < 2.7 Pt Resolution: ~ 10% @ 1 TeV/c < 3 % P t <250 GeV/c End cap: 1 < |  | < 2.7 Tracking with MDTs & CSCs Triggering with TGCs Barrel: |  | < 1.0 Tracking with MDTs Triggering with RPCs

6. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 5 S.M. Higgs search Muons relevant for Trigger and ID in the full energy range M H = 130 GeV muon spectrometer standalone Standalone measurement better than Inner Detector for M H >180 GeV

7. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 6 MSSM Higgs Bosons search m h < 135 GeV m A  m H  m H  at large m A A, H, H  cross-section ~ tg 2  Best sensitivity from A/H  , H    bbA/H   : -- covers good part of region not excluded by LEP -- experimentally easier than A/H   -- crucial detector : Muon Spectrometer (high-p T muons from narrow resonance) Relevant for mass and couplings measurement 5  discovery curves  m ~11 GeV A/H  , tg  = 38

8. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 7 CSC MDT+RPC MDT+TGC Signals and Backgrounds Expected bkg rate Single counting rate: Barrel < 40 Hz/cm 2 End Cap 20-1000 Hz/cm 2 Low Pt trigger High Pt trigger Photons and Neutrons are the main source of uncorrelated background Muon rates

9. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 8 Resolution Resolution limited by :  M.S. and Energy Loss Fluct. @ 3% for 10 < Pt < 250 GeV/c for 10 < Pt < 250 GeV/c  Chamber Resolution and Alignment for Pt > 250 GeV/c for Pt > 250 GeV/c Energy loss fluctuations Multiple scattering Chamber resol and align. Muon spectrom. standalone Inner tracker stand alone The muon spectrometer resolution dominates for Pt > 100 GeV/c

10. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 9 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

11. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 10 Barrel toroid status The completion of these components is expected by May 2003 Conductor double Pancake: 14 out of 16 ready Cryostat vacuum vessel: 5 out of 8 delivered

12. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 11 End Cap Toroids Services Turret Magnet Coils (4.5K) Thermal Radiation Shield (80K) Vacuum Vessel (300K) Pancakewindings: 8 of 16 done Vacuum vessels delivered at CERN

13. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 12 Field Maps Field Integral vs  X (cm) Y (cm) Need to measure accurately the coordinate in the non bending plane the non bending plane RPC and TGC Field integral inhomogeneous in the tracking volume More than a single RT relation per wire Need to take into account the differences in Need to take into account the differences in Lorentz angle for the calibration of the Lorentz angle for the calibration of the precision chambers precision chambers

14. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 13 Trigger concept  Trigger algorithm relies on pointing coincidences in on pointing coincidences in two views of two (low Pt) two views of two (low Pt) or three (high Pt) units of or three (high Pt) units of trigger detectors trigger detectors  Trigger detectors must have very good timing have very good timing properties to allow bunch properties to allow bunch crossing ID crossing ID  Low Pt trigger Thr @ 6 GeV/c  High Pt trigger Thr @ 20 GeV/c  Trigger Coverage |  | < 2.4

15. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 14 Trigger efficiency and rates Muon trigger rate @ 10 33 cm -2 s -1 : Low Pt (> 6 GeV/c) 10 KHz Low Pt (> 6 GeV/c) 10 KHz High Pt (> 20 GeV/c) 200 Hz High Pt (> 20 GeV/c) 200 Hz Pt Gev/c Luminosity Barrel Trigger rate (Hz) 10 2 10 3 10 4 Luminosity Barrel 10 4 10 3 Trigger rate (Hz) Good safety margin over accidental trigger rate

16. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 15 Barrel Trigger chambers: RPC Operating Conditions (E gas ~ 5 KV/mm) Gas: C 2 H 2 F 4 96.7% - C 4 H 10 3% - SF 6 0.3% ;  bakelite ~ 2x10 10  cm ; Gas Gap d = 2 mm ; Graphite coated HV electrodes Cu read out strips 30 mm pitch Time resolution ~1.5 ns Bakelite Plates Foam PET spacers Graphite electrodes X readout strips HV Y readout strips Grounded planes Gas Gas Volume + spacers Read out strips Read-out electronics 8 chs Ga-AS 3 stage ampli.+discrim

17. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 16 Test rate: 8 chambers/week Time Plateau efficiency V-I curve Noise Muon radiography Tests on Production chambers RPC Cosmic Test Station RPC Muon Radiography: Innefficiency only close to spacer positions

18. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 17 RPC Ageing test 3 production RPCs currently ageing at the CERN Gamma Irradiation Facility  Aim to integrate 300 mC/cm 2  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 25 30 Total charge (mC/cm 2 ) 15 mC/10 Days time Integrated charge

19. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 18 END CAP Trigger Chambers: TGCs 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 % CO 2, 45 % N-Pentane HV: 3.1 KV Saturated avalanche mode Very short drift time due to the thin gap ensures the good time resolution needed for Bunch Crossing ID Wire signal used to provide the trigger, strip signals used for the second coordinate

20. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 19 Results from high rate test Efficiency at ~ 1 kHz/cm 2 Efficiency with source off 25 ns 100 % hit time distrib. % hits in window 20 40 60 Time (ns) 20 40 60 Time (ns)

21. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 20 Trigger Efficiency under irradiation ~ 1 kHz/cm 2

22. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 21 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  m per plane reading charge on the cathode strips Good time resolution: 7 ns Due to small drift time (30 ns) 4 planes per chamber

23. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 22 Results from high rate test Inefficiency vs Rate Inefficiency vs Rate Inefficiency= distance from track > 300  m Resolution vs Rate Resolution vs Rate The expected background rate at  =2.7 is 2.7 KHz/cm 2 (with safety factor 5) The CSC System can provide very good space resolution Distributions of residuals: Reconstructed CSC track position - Silicon Telescope extrapolation  Tails mainly due to  -electrons at low rate, and to overlapping at low rate, and to overlapping signals at high rate. signals at high rate. 47  m Low Rate 0.1 KHz/cm 2 Low Rate 0.1 KHz/cm 2 69  m High Rate 2.3 KHz/cm 2 High Rate 2.3 KHz/cm 2

24. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 23 Precision Chambers: MDTs Drift tubes mechanical parameters: Tube Radius : 15 mm Tube thickness 400  m Wire diameter. 50  m Tube length: 1-6 mt Chamber mech. Precision 20  m Operating Conditions Gas Mixture: 93 % Ar 7% CO 2 Absolute pressure: 3 Bar HV: 3080 V Gas Gain: 2x10 4 Threshold: 25 electrons Reconstructedtrack

25. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 24Resolution Muon Spectrometer resolution @ High Pt depends crucially on Single station space resolution (6-8 meas.) Low Rate 40-60  m High Rate 40-90  m Radius mm Space charge effect on the single tube resolution Resolution (mm)  Single tube resolution  Precise knowledge of space-time calibration (RT-Rel) space-time calibration (RT-Rel)  Alignment Space charge fluctuations at high irradiation worsen the resolution far away from the wire

26. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 25 RT-Relation Drift time (ns) True RT - calibration (  m) The RT-relation close to the wire is distorted by Threshold effects -25  m +25  m RT relation known at the level of 25  m over almost all the drift distance

27. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 26 Barrel Alignment The relative chamber positions should be known with ~30  m precision to ensure high Pt resolution  alignment system based on optical elements on optical elements (RASNIK) to reconstruct (RASNIK) to reconstruct and monitor the geometry and monitor the geometry of the spectrometer with of the spectrometer with the required accuracy the required accuracy  Projective Lines to monitor relative movements of stations  Axial lines to monitor chambers movement within a station Projective lines (RASNIK) Axial lines (RASNIK) Station 1 Station 2 Station 3

28. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 27 Survey platforms 2 BML on rails Projective platform BML on rail BIL on rail 2002: Barrel & End Cap System Test Test the barrel and end-cap alignment concepts  Test the barrel and end-cap alignment concepts  Test system and chamber performances with a barrel and end cap sector (6+6 chambers) Barrel Sector End Cap Sector End Cap Stand Barrel Stand Magnet on Virtual IP

29. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 28 Alignment test result  Displace one chamber from middle station, along supporting rail  Check alignment reconstructed position against track reconstructed position track reconstructed position 2.0 1.5 1.0 0.5 21.51.00.5 Displacements from track reconstruction (mm) Displacements from track reconstruction (mm) Displacement from alignment system (mm) The 15  m RMS of the residuals distribution proves the correctness of the alignment system concept Residual difference between chamber position using tracks and alignment system 20 40 60 0 -20 -40 -60 0.51.51.02.0 Position (mm) Residuals  m RMS = 15  m

30. Fermilab 1/5/03Ludovico Pontecorvo – CERN/INFNATLAS MUON 29 Conclusions Construction and Tests: What’s Next?  System Test with Tracking and Trigger chambers  Trigger System Test The ATLAS Muon Spectrometer will provide powerful  The ATLAS Muon Spectrometer will provide powerful muon trigger and identification over the full energy range muon trigger and identification over the full energy range with a large angular acceptance with a large angular acceptance   The very good momentum resolution will ensure high quality stand alone measurement for most of the physics channels stand alone measurement for most of the physics channels under study (H->4 , A-> , Z’->  under study (H->4 , A-> , Z’->   The Magnet systems are well advanced in the construction Trigger and Precision chambers are under construction  Trigger and Precision chambers are under construction The chambers performance at high rate  The chambers performance at high rate is adequate to the LHC environment is adequate to the LHC environment The alignment concept is validated by the results from  The alignment concept is validated by the results from the 2002 System Test of a full sector of barrel and the 2002 System Test of a full sector of barrel and end-cap precision chambers end-cap precision chambers