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Muon detector

Muon detector. S.Tanaka (KEK). Contents. Introduction About Muon Spectrometer ATLAS CMS Fundamentals of wire chambers Performance of Muon Spectrometer Summary. References. ATLAS Muon TDR http://atlas.web.cern.ch/Atlas/GROUPS/MUON/TDR/Web/TDR_chapters.html CMS Muon TDR

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Muon detector

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  1. Muon detector S.Tanaka (KEK)

  2. Contents • Introduction • About Muon Spectrometer • ATLAS • CMS • Fundamentals of wire chambers • Performance of Muon Spectrometer • Summary

  3. References • ATLAS Muon TDR • http://atlas.web.cern.ch/Atlas/GROUPS/MUON/TDR/Web/TDR_chapters.html • CMS Muon TDR • http://cmsdoc.cern.ch/cms/TDR/MUON/muon.html

  4. Introduction • How to select the interest muon tracks • Muon spectrometer • Magnets • Trackers • How to optimize the parameters of muon spectrometer • Efficiency • Radiation hardness • Long term stability • Costs

  5. The ATLAS Muon Spectrometer ATLAS:A Toroidal LHC ApparatuS • Muon Spectrometer: • toroidal magnetic field: <B> = 4 Tm •  high pt-resolution independent • of the polar angle • size defined by large lever arm to • allow high stand-alone precision • air-core coils tominimise the • multiple scattering • 3 detector stations • - cylindrical in barrel • -wheels in end caps • coverage:|| < 2.7 • Trackers: • fast trigger chambers: TGC,RPC • high resolution tracking detectors: MDT,CSC

  6. CMS Muon Spectrometers CMS:A Compact Muon Solenoidal detector of LHC Muon detector coverage:|| < 2.4 Magnetic Field =4 Tesla

  7. Difference of 2 type magnetic fields *Large size area with high magnetic field *Non-uniform field *Field always perpendicular to momentum *Large Homogenous field inside coil *Weak opposite field in return yoke *Size limited

  8. 6m ←ATLAS：Troidal magnetic field 　　（y-z view) 3m CMS: Solenoidal magnetic Field → (r-φview)

  9. Momentum measurement CMS 8 % @ 100GeV ATLAS 2.5 %@100GeV

  10. How to measure Pt? Measure the transverse component to B field Position resolution s(x) for each Pt resolution depends on B, L and s(x)(not R)!

  11. Important parameters for Pt • Position resolution of Precision chamber • Alignment calibration of chambers • Magnetic field calibration • Distance between chambers • Energy loss by inside materials • Multiple scattering effects • Uniformity of the B field and precision chamber acceptance • Performance stability on high flux irradiation

  12. Interaction of charged particle Rutherford scattering An incoming particle with charge z interacts elastically with a target of nuclear charge Z. The cross-section for this e.m. process is z: Charge of incident particle Z: Atomic number of material Approximation - Non-relativistic - No spins • Scattering does not lead to significant energy loss

  13. Interaction of charged particle • Multiple scattering (Moliere formula) • Approximates the projected scattering angle of multiple scattering by a Gaussian, with a width • Approximation X0 : Radiation length (Mean distance over which a high energy electron loses all but 1/e of its energy by bremsstrahlung, and 7/9 of the mean free path for pair production by a high-energy photon.) X: charge Rutherford scattering

  14. Interaction of charged particle • What is the contribution of multiple scattering to Momentum resolution? Independent of Pt More Precisely →

  15. Muon Spectrometer Concept • For reconstructed mass resolution (ex. H → 4μ, Z → 2μ) Need good transverse momentum resolution ~2%:ATLAS , 7~8%:CMS for 5-100 GeV • For charge identification (ex. Z’→mm) • Need Good position resolution • For CP-violation and B and Top physics Trigger selectivity : High Pt (~20 GeV) and Low Pt (~ 6 GeV) • For bunch-crossing identification (Trigger) Time resolution: < 25 ns ・Standalone muon system ・Dedicated chambers each for tracking and triggering ATLAS:MDT+RPC for Barrel, MDT+TGC for End-cap CMS:DT+RPC for Barrel, CSC+RPC for End-cap ・Superconducting magnet ⇒

  16. Toroid magnet (ATLAS) • Current=20.5kA • 25.3 m length • 4 T on superconductor

  17. Magnetic field and Pt resolution (ATLAS) Integrated magnetic field as a function of h Acceptance as a function of h Pt Resolution h h

  18. Solenoid magnet (CMS) • 4 T superconducting solenoid • 13m length • Inner diameter : 5.9m

  19. Magnetic field and Pt resolution (CMS) Acceptance as a function of h Integrated magnetic field as a function of h

  20. Muon Chambers • ATLAS • Monitored Drift Tube (Barrel, End-cap Precision) • Resistive Plate Chamber (Barrel Trigger) • Thin Gap Chamber (End-cap Trigger) • Cathode Strip Chamber (Forward Precision) • CMS • Drift Tube (Barrel Precision) • Resistive Plate Chamber (Barrel + End-cap Trigger) • Cathode Strip Chamber (End-cap Precision) (Tracking chamber => Gas chamber!)

  21. How to read the signal?

  22. Energy loss of charged particle Bethe-Bloch formula (ionizing particle): (Max kinetic energy, which can transferred to electron) A: mass number [g/mol] of the material z: Charge of incident particle Z: Atomic number of material d: Density correction I : Mean excitation energy of material I=I0Z

  23. Energy loss of charged particle • We should also consider bremsstrahlung for high energy muon (>100 GeV)

  24. Ionization Incident particle interact with gas molecule, then producing electron and ion pairs (nprim). nprim has relationship with average Z of gas molecule This primary electrons are energetic enough to ionize other molecule (secondary : ns ~3)

  25. Properties of several gases used in proportional counters (from different sources, see the References section). Energy loss and ion pairs (i.p.) per unit length are given at atmospheric pressure for minimum ionizing particles

  26. Ionization • Total number of electron :ntot=nprim+ns=dE/Wi • Wi [eV/cm]: Effective energy to produce ion-electron pair Ex: Consider Ar(70)+Isobutane(30) ntot=2440/24 *0.7 + 4500/23 * 0.3 =124 pair/cm nprim= 29.4 * 0.7 + 46 * 0.3 =34 pair/cm

  27. Electron Drift In the absence of electric fields electron –ion pairs recombine and the net liberated charges disappear. In a uniform electric field the motion of electrons and ions alternate between acceleration and collision with the gas molecules. The resulting motion, in both cases, is a uniform velocity which depends on the intensity of the electric field and the properties of the gases. MWPC Cylindrical

  28. Position measurement with Drift chamber Measure arrival time of electrons at sense wire relative to a time t0.

  29. Gas amplification Townsend avalanche: a: first townsend coefficient E/p > 10^4/cm If we neglect the space-charge effect and photoelectriceffect by de-excitation of molecule, total charge (Q) = n0eM M (gas amplification factor) is written as a function of a (a: radius of wire) Induced signal is written as

  30. Choice of gas • In the avalanche process molecules of the gas can be brought to excited states. Solution: addition of polyatomic gas as a quencher Absorption of photons in a large energy Range. Energy dissipation by collisions or dissociation into smaller molecules. ⇔penning effect

  31. Operation mode M < 104: Ionization mode (using DC mode for radiation monitor) M > 104 :Proportional mode (MWPC, DC) M > 106 : Limited Proportional mode M > 108 :G.M mode or Streamer mode (survey meter)

  32. Difference between G.M and Streamer G.M mode Large output signal Long dead time Long term stability Streamer mode Large output signal Short dead time Large discharge sometime occur Limited mean free path of photon

  33. HV dependence of Output charge (ex.RPC) Streamer Limited proportional Proportional

  34. Monitored Drift Tube (ATLAS) • 6 / 8 drift tube layers,arranged in • 2 multilayersglued to a spacer frame • length: 1 – 6 m, width: 1 – 2 m • optical system to monitor chamber • deformations • gas: Ar:CO2 (93:7) to prevent aging, 3 bar • chamber resolution: 50 µm • single tube resolution: 100 µm • required wire position accuracy: 20 µm Barrel End Cap

  35. MDT (Layout) BOL Number of MDT : 1194 Number of Channels: 370000 Area: 5500 m2 BOS BML BMS BIL BIS

  36. tube wall: 0.4 mm Al 30 mm diameter endplug wire: 50 µm W-Re Monitored Drift Tube (ATLAS) a= 25 μm b= 30mm gas: Ar:CO2 (93:7) Position resolution: 50 µm  monitoring of high mechanical precisionduring production

  37. MDT (Wire Positions with a X-Ray Method) measurement of the intensity as function of the motor position X-tomograph at CERN accuracy of wire position measurement: 3 µm mechanical precision measured with X-ray method selected chambers tested: 74 of 650 chambers produced at 13 sites scanned sofar average wire positioning accuracy: 15 µm

  38. MDT (Cosmic ray test) • goals: • check functionality of all • tubes and electronics channels • measurement of wire positions e.g. Test Facility at the University of Munich y z • deviations from nominal positions compared • to X-ray results: rmsy = 25 µm, rmsz = 9 µm

  39. MDT (Tracking efficiency) track-reconstruction efficiency • total track-reconstruction efficiency: • ( 99.97 )% without irradiation • ( 99.77 )% at highest ATLAS rate • (for 4m long tubes) +0.03 - 0.9 +0.23 - 0.8 • even at highest expected irradiation no deterioration of track-reconstruction efficiency

  40. Drift Tube (CMS) • Gas : Ar(85) + CO2(15) • HV = 3.6 kV • Spatial Resolution: 100μm • (Single cell space resolution : < 250μm)

  41. Drift Tube (Layout: CMS)

  42. Drift Tube (CMS) HV=3600 V cm

  43. Drift Tube (Tracking efficiency:CMS)

  44. Cathode Strip Chamber (ATLAS,CMS) • 50mm wire spaced by 3.2mm • gas :Ar(40%)+CO2(50%) +CF4(10%) • HV~3.6 kV • 9.5 mm gas gap • Special resolution < 100μm

  45. CSC (ATLAS,CMS)

  46. CSC (ATLAS,CMS) S = d = 2.54 mm W = 5.6 mm 32 four-layer chambers 2.0 < |h| < 2.7 |Z| ~ 7m, 1 < r < 2 m 4 gas gaps per chamber 31,000 channels Gas Ar:CO2:CF4 (30:50:20) High voltage :3.2 kV

  47. Multiwire proportional chambersdetermine muon position by interpolating the charge on 3 to 5 adjacent strips • Precision (x-) strip pitch ~ 5mm • Spatial resolution s ~ 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.

  48. Resistive Plate Chamber (ATLAS,CMS) • gas: C2H2F4:isoC4H10 (97:3) • 2mm gas gap • HV=9kV

  49. RPC (ATLAS,CMS) • Resistive Plate Chambers are gaseous, self-quenching parallel-plate detectors. • They are built from a pair of electrically transparent bakelite plates separated by small spacers. Signal are induced capacitively on external readout strips. - 420.000 channels in 596 double gap chambers. Gas: C2H2F4:isoC4H10 (97:3). HV : 9kV. Performance: -efficiency:>99%. -space-time resolution of 1cm1ns. -rate capability:~1kHz/cm².

  50. 1.3m 1.4m Thin Gap Chamber (ATLAS) Requirements on ATLAS: • Fast signal response (<25ns) • High efficiency (>99 %) • Radiation-proof (~0.6C/cm) • Rate capability (~kHz/cm2) ASD: Amp. Shaper Discriminator

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