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The Challenge of Detecting and Measuring Muons at the LHC

The Challenge of Detecting and Measuring Muons at the LHC. V. Polychronakos Physics Department Brookhaven National Laboratory. Overview. The Importance of Muons for the LHC Physics The Requirements of a Muon System Technology Choices

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The Challenge of Detecting and Measuring Muons at the LHC

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  1. The Challenge of Detecting and Measuring Muons at the LHC V. Polychronakos Physics Department Brookhaven National Laboratory EESFYE - HEP2006

  2. Overview • The Importance of Muons for the LHC Physics • The Requirements of a Muon System • Technology Choices • Principles of Operation of “Old Technologies” adapted for the demanding performance at the LHC • The Monitored Drift Tube Chambers • Cathode Strip Chambers • Constraints of the Magnetic Field in the choice of Detectors • Alignment • Some current photographs from the ATLAS Installation • Concluding Comment EESFYE - HEP2006

  3. Experiments at the LHC • Four Experiments being constructed: • “General Purpose” ATLAS and CMS • 4-pi Geometry • Electroweak Symmetry Breaking (Higgs Boson) • Supersymmetry • Compositness • New Vector Bosons? • Extra Dimensions? • …… • ALICE – Heavy Ion Experiement (akin to PHENIX) • LHCb – Dedicated “b-physics” Experiement (CP violation in the b sector ) EESFYE - HEP2006

  4. LHC Footprint ` LEP Tunnel reused 27 km circumference CMS LHCb ALICE ATLAS EESFYE - HEP2006

  5. Importance of Muons, an Example Higgs Discovery Potential (ATLAS example but CMS is similar) High mass: MH > 180GeV H->ZZ->4lepton Has a narrow peak on top of a low background (pp->ZZ) Intermediate mass: 115 < MH < 180GeV Challenging for MH < 130GeV EESFYE - HEP2006

  6. SM Higgs with mH ~ 150 GeV • Events observed with 4e, 4m and 2e2m final states • Clear mass peak with S/B >> 1 EESFYE - HEP2006

  7. The ATLAS Muon System EESFYE - HEP2006

  8. The CMS Experiment EESFYE - HEP2006

  9. Requirements for an LHC Muon System • Trigger: • Detectors with fast timing resolution ~2 ns, • ~ 1 cm spatial resolution in momentum plane • ~few cm spatial resolution in transverse coordinate (if precision chambers can not provide it) • Be able to handle high rates (~20(h=0)-1000(h=2.7) Hz/cm2) • Cover large Areas and be affordable • Momentum measurement chambers (Precision Chambers): • ~80 micron spatial resolution • ~few cm spatial resolution in transverse coordinate • Be able to handle high rates (~20-1000 Hz/cm2 • Cover large Areas and be affordable • Alignment to ~30 mm needed EESFYE - HEP2006

  10. Requirements for an LHC Muon System • Trigger: • Detectors with fast timing resolution ~2 ns, • ~ 1 cm spatial resolution in momentum plane • ~few cm spatial resolution in transverse coordinate (if precision chambers can not provide it) • Be able to handle high rates (~20(h=0)-1000(h=2.7) Hz/cm2) • Cover large Areas and be affordable • Momentum measurement chambers (Precision Chambers): • ~80 micron spatial resolution • ~few cm spatial resolution in transverse coordinate • Be able to handle high rates (~20-1000 Hz/cm2 • Cover large Areas and be affordable • Alignment to ~30 mm needed EESFYE - HEP2006

  11. Triggering on Muons ATLAS Example) EESFYE - HEP2006

  12. Requirements for an LHC Muon System • Trigger: • Detectors with fast timing resolution ~2 ns, • ~ 1 cm spatial resolution in momentum plane • ~few cm spatial resolution in transverse coordinate (if precision chambers can not provide it) • Be able to handle high rates (~20(h=0)-1000(h=2.7) Hz/cm2) • Cover large Areas and be affordable • Momentum measurement chambers (Precision Chambers): • ~80 micron spatial resolution • ~few cm spatial resolution in transverse coordinate • Be able to handle high rates (~20-1000 Hz/cm2 • Cover large Areas and be affordable • Alignment to ~30 mm needed EESFYE - HEP2006

  13. Importance of Large |h| coverage EESFYE - HEP2006

  14. Requirements for an LHC Muon System • Trigger: • Detectors with fast timing resolution ~2 ns, • ~ 1 cm spatial resolution in momentum plane • ~few cm spatial resolution in transverse coordinate (if precision chambers can not provide it) • Be able to handle high rates (~20(h=0)-1000(h=2.7) Hz/cm2) • Cover large Areas and be affordable • Momentum measurement chambers (Precision Chambers): • ~80 micron spatial resolution • ~few cm spatial resolution in transverse coordinate • Be able to handle high rates (~20-1000 Hz/cm2 • Cover large Areas and be affordable • Alignment to ~30 mm needed EESFYE - HEP2006

  15. What dictates Size and Precision • Sagitta for 1 TeV/c muon in a typical • Spectrometer ( B = 1 Tesla • L = 6 m) • S = 1.4 mm • If we want to measure p to 5% • ds = 70 microns • Large area, high precision detectors EESFYE - HEP2006

  16. The stand-alone momentum resolution of the CMS muon spectrometer is typical for an iron-core system DpT/pT~ 710% for pT = 10100 GeV Due to the air-core configuration, ATLAS achieves a very good stand-alone resolution DpT/pT~ 2% for pT = 10100 GeV pT (GeV) Resolution on Muon Momentum CMS ATLAS EESFYE - HEP2006

  17. Muon Momentum Resolution(cont.) ATLAS Air core Toroidal Magnet System results in excellent stand-alone performance Fundamental difference from CMS where Inner Tracking System is required for good resolution in the range of 10-100 GeV/c. Stand-alone resolution limited to ~10% due to multiple scattering CMS EESFYE - HEP2006

  18. Detector Choices • Proportional and Drift Chambers the Detector of choice for Muon Spectrometers both for trigger (proportional) and for momentum measurement (both) for the last ~40 years! • Assuming a MWPC with d=3 mm wire spacing the spatial resolution is limited to ~1mm (d/sqrt(12)) and the timing to an rms of ~7 ns; neither appropriate for, e.g., ATLAS • Conventional Drift Chambers can provide a factor of 3-5 better resolution but still not good enough • Trigger is even tougher • Resistive Plate Chambers, RPC, is (just about) the only detector considered in spite of the problems they’ve had in experiments using them • ATLAS uses Thin Gap Chambers, TGC, in its Endcaps. They are modified MWC with very small gap, running in saturated mode, with resistive cathodes achieving 2-3 ns rms timing resolution EESFYE - HEP2006

  19. The ATLAS Muon System • Trigger Chambers • Resistive Plate Chambers (RPC) in Barrel • Thin Gap Chambers (TGC) in the Endcaps • Momentum measurement chambers • Monitored Drift tubes (MDT) in most of the solid angle • Cathode Strip Chambers (CSC) in the most forward (high rate) Endcap region EESFYE - HEP2006

  20. The Monitored Drift Tube Chamber EESFYE - HEP2006

  21. Assembly of MDT Chambers (Frascati, IT) EESFYE - HEP2006

  22. An Orthogonal (Barrel) Chamber (EMS, U. Michigan) EESFYE - HEP2006

  23. Barrel Chamber (MPI, Munich) EESFYE - HEP2006

  24. Cosmic muon test/commissioning EESFYE - HEP2006

  25. Cathode Strip Chambers, CSCPrinciple of operation Proportional Chambers with segmented cathodes. The wires are not read (could be read to provide transverse coordinate, CMS) Determine muon position by interpolating the charge on 3 to 5 adjacent strips Precision (x-) strip pitch ~ 5.6 mm Measure Q1, Q2, Q3… with 150:1 SNR to get sx ~ 60 mm. Second set of y-strips measure transverse coordinate to ~ 1 cm. Position accuracy unaffected by gas gain or drift time variations. Accurate intercalibration of adjacent channels essential. S = d = 2.54 mm W = 5.6 mm EESFYE - HEP2006

  26. CSC Fabrication @ BNL Cathode Parts Measurement of Planarity Cathode Panel Lamination Storage of completed panels Wire Winding EESFYE - HEP2006

  27. CSC Features • Excellent resolution up to 50 microns • Fairly Good timing resolution – adequate for LHC if several layers used and first arrival chosen • Can provide Trigger Primitives • Cathodes can be segmented almost arbitrarily to accommodate varying requirements of resolution, occupancy • Immune to variations of gain, pressure, temperature (relative measurement) EESFYE - HEP2006

  28. So, why not use them everywhere? • Need fairly fine segmentation for good resolution (large number of channels) • The issue of inclined tracks Presicion along the anode wire Normal tracks deposit charge on one point Inclined tracks deposit charge on a finite length of wire Landau Fluctuations shift C.G. of Charge spoiling the resolution EESFYE - HEP2006

  29. The Problem of Inclined Tracks Resolution proportional to tan(q) s<100 microns, limits the incident angle to ~2x0.15 rad At a distance of, say, 5 m from the interaction point implies max width of the chamber to 1.5m 1.5 m is also close tothe maximum length of unsupported 30 m tungsten wire EESFYE - HEP2006

  30. The Case of Magnetic Field Solenoid chambers inclined by Lorentz angle qL Toroid Inclination of chambers to mitigate The inclined track problem would Result in a Spherical Detector Geometry! EESFYE - HEP2006

  31. EESFYE - HEP2006

  32. Alignment System In order to be able to use precision of ~50 m, one needs to know the relative position of the chambers to better than ~30m EO Layer ATLAS Concept (Endcaps) Set of radial precision bars connected by projective instrumented lazer beams and proximity sensors to the chambers EM Layer Alignment Bar Sensor Alignment Line EI Layer EESFYE - HEP2006

  33. November 2005 EESFYE - HEP2006

  34. The Electromagnetic Calorimeter Cryostat EESFYE - HEP2006

  35. The Muon Spectrometer (installation) We are installing the most difficult chambers ~25 % done EESFYE - HEP2006

  36. The Muon Spectrometer (wheels) Big wheels sectors integration at CERN EESFYE - HEP2006

  37. Concluding Remarks • High momentum, size, required precision, timing make muon measuremnet at the LHC quite Challenging • Variations of Drift Chambers as well as Cathode Strip Chambers used for the precision momentum measurement • All four Experiments use some variant of the CSC • CMS, with a Solenoid field, akes the most extensive use in their Endcaps (also provide the trigger) • ATLAS uses tem in the very forward region of the first meaurement extending the coverage to |h|=2.7 • ALICE uses them, in a pixel form, also in their muon spectrometer to handle the large charged particle densities • Extensive use of Large, precision Drift Chambers are extensively being used EESFYE - HEP2006

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