Muon detector

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Muon detector

• S.Tanaka (KEK)

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Contents

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

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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

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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

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The ATLAS Muon Spectrometer
ATLAS A Toroidal LHC ApparatuS

• Muon Spectrometer
• toroidal magnetic field ltBgt 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 to minimise the
• multiple scattering
• 3 detector stations
• - cylindrical in barrel
• - wheels in end caps
• coverage ? lt 2.7

• Trackers
• fast trigger chambers TGC, RPC
• high resolution tracking detectors MDT,CSC

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CMS Muon Spectrometers
CMSA Compact Muon Solenoidal detector of LHC
Muon detector coverage ? lt 2.4 Magnetic Field
4 Tesla
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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
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6m
?ATLASTroidal magnetic field (y-z view)
3m
CMS Solenoidal magnetic Field ? (r-fview)
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Momentum measurement
CMS 8 _at_ 100GeV
ATLAS 2.5 _at_100GeV
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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)!
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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

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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
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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
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Interaction of charged particle

• What is the contribution of multiple scattering
  to Momentum resolution?

Independent of Pt
More Precisely ?
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Muon Spectrometer Concept

• For reconstructed mass resolution (ex. H ? 4µ,
  Z ? 2µ) Need good transverse momentum resolution
  2ATLAS , 78CMS 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 lt 25 ns

Standalone muon system Dedicated chambers each
for tracking and triggering ATLASMDTRPC
for Barrel, MDTTGC for End-cap CMSDTRPC
for Barrel, CSCRPC for End-cap Superconducting
magnet
?
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Toroid magnet (ATLAS)

• Current20.5kA
• 25.3 m length
• 4 T on superconductor

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Magnetic field and Pt resolution (ATLAS)
Integrated magnetic field as a function of h
Acceptance as a function of h
Pt Resolution
h
h
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Solenoid magnet (CMS)

• 4 T superconducting solenoid
• 13m length
• Inner diameter 5.9m

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Magnetic field and Pt resolution (CMS)
Acceptance as a function of h
Integrated magnetic field as a function of h
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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 gt Gas chamber!)

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How to read the signal?
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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 II0Z
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Energy loss of charged particle

• We should also consider bremsstrahlung for high
  energy muon (gt100 GeV)

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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)
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Gas Z A d(g/cm3) Ei (eV) I0 (eV) Wi dE/dx dE/dx np (i.p.) /cm) nt (i.p.) /cm)
Gas Z A d(g/cm3) Ei (eV) I0 (eV) Wi (MeV cm2/g) (keV/cm) np (i.p.) /cm) nt (i.p.) /cm)
H2 2 2 8.3810-5 15.9 15 37 4.03 0.34 5.2 9.2
He 2 4 1.6610-4 24.5 25 41 1.94 0.32 5.9 7.8
N2 14 28 1.1710-3 16.7 16 35 1.68 1.96 10 56
O2 16 32 1.3310-3 12.8 12 31 1.69 2.26 22 73
Ne 10 20.2 8.3910-4 21.5 22 36 1.68 1.41 12 39
Ar 18 39.9 1.6610-3 15.7 16 26 1.47 2.44 29.4 94
Kr 36 83.8 3.4910-3 13.9 14 24 1.32 4.6 22 192
Xe 54 131.3 5.4910-3 12.1 12 22 1.23 6.76 44 307
CO2 22 44 1.8610-3 13.7 14 33 1.62 3.01 34 91
CH4 10 16 6.7010-4 15.2 13 28 2.21 1.48 16 53
C4H10 34 58 2.4210-3 10.6 11 23 1.86 4.5 46 195
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
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Ionization

• Total number of electron ntotnprimnsdE/Wi
• Wi eV/cm Effective energy to produce
  ion-electron pair
• Ex Consider Ar(70)Isobutane(30)
• ntot2440/24 0.7 4500/23 0.3 124 pair/cm
• nprim 29.4 0.7 46 0.3 34 pair/cm

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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
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Position measurement with Drift chamber
Measure arrival time of electrons at sense wire
relative to a time t0.
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Gas amplification
Townsend avalanche
a first townsend coefficient E/p gt 104/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
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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
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Operation mode
M lt 104 Ionization mode (using DC mode for
radiation monitor) M gt 104 Proportional
mode (MWPC, DC) M gt 106 Limited Proportional
mode M gt 108 G.M mode or Streamer
mode (survey meter)
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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
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HV dependence of Output charge (ex.RPC)
Streamer
Limited proportional
Proportional
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Monitored Drift Tube (ATLAS)

• 6 / 8 drift tube layers, arranged in
• 2 multilayers glued to a spacer frame
• length 1 6 m, width 1 2 m
• optical system to monitor chamber
• deformations
• gas ArCO2 (937) to prevent aging, 3 bar
• chamber resolution 50 µm
• single tube resolution 100 µm
• required wire position accuracy 20 µm

Barrel
End Cap
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MDT (Layout)
BOL
Number of MDT 1194 Number of Channels
370000 Area 5500 m2
BOS
BML
BMS
BIL
BIS
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Monitored Drift Tube (ATLAS)
a 25 µm b 30mm gas ArCO2 (937)
Position resolution 50 µm ? monitoring of high
mechanical precision during production
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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 so far
average wire positioning accuracy 15 µm
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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

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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

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Drift Tube (CMS)

• Gas Ar(85) CO2(15)
• HV 3.6 kV
• Spatial Resolution 100µm
• (Single cell space resolution
• lt 250µm)

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Drift Tube (Layout CMS)
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Drift Tube (CMS)
HV3600 V
cm
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Drift Tube (Tracking efficiency CMS)
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Cathode Strip Chamber (ATLAS,CMS)

• 50mm wire spaced by 3.2mm
• gas Ar(40)CO2(50)
• CF4(10)
• HV3.6 kV
• 9.5 mm gas gap
• Special resolution lt 100µm

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CSC (ATLAS,CMS)
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CSC (ATLAS,CMS)
S d 2.54 mm W 5.6 mm
32 four-layer chambers 2.0 lt h lt 2.7 Z 7m,
1 lt r lt 2 m 4 gas gaps per chamber 31,000
channels Gas ArCO2CF4 (305020) High voltage
3.2 kV
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• Multiwire proportional chambers determine 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.

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Resistive Plate Chamber (ATLAS,CMS)

• gas C2H2F4isoC4H10 (973)
• 2mm gas gap
• HV9kV

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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 C2H2F4isoC4H10 (973). HV
9kV. Performance -efficiencygt99. -space-time
resolution of 1cm1ns. -rate capability1kHz/cm².
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Thin Gap Chamber (ATLAS)

• Requirements on ATLAS
• Fast signal response (lt25ns)
• High efficiency
• (gt99 )
• Radiation-proof
• (0.6C/cm)
• Rate capability
• (kHz/cm2)

ASD Amp. Shaper Discriminator
Wire potential 3.0 kV
Gas mixture CO2 n-pentane (55) (45)
Wire diameter 50 mm
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TGC performance (ATLAS)
Efficiency map (KOBE Univ.)
Incident angle dependence of drift time
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TGC Production Procedure
Graphite spraying
Checking quality
80 boards/month
4 board /day
Mounting Read-out boards 1 Unit/day 3 persons
FR4 Frame Gluing
Wire winding
2 boards /day 1 person
4 boards/day 3 persons
Making doublet (triplet)
Singlet closing
1 Unit/day 2 persons
2 TGCs /day 3 persons
Paper honeycomb
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TGC Quality Control

• TGC is fabricated by the gluing processes
• (we can no longer reopen it after closing TGC).
• We have to control the surface distortion less
  than 200 mm
• We apply following tests
• Measurement of the surface resistance of cathode
  after the graphite spraying,
• High voltage test before and after closing
  singlet TGC,
• Pulse test after mounting adapter board and
• High voltage test after mounting adapter board.
• Pulse response check by b-ray radioactive source
• Cosmic ray test at KOBE Univ.

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Graphite spraying and FR4 frame Gluing

• Graphite spraying by automatic sprayer
• two-dimensional linear actuator
• spray gun by the pneumatic control

•  AT FR4 Frame gluing
• To control the quality of epoxy adhesive.
• Screen painting method for parts and
• Auto dispenser for button supports
• are adopted.

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Wire winding

• Washing machine
• to remove some dusts on the cathode plane by
  mist.
• Washing away the solder flux with ultrasonic
  cleaning
• (water-soluble flux is used)

• Wire winding machine
• Consists of a linear actuator and
• a rotating table.
• Total 800,000 wires
• Anode Wire Gold plated Tungsten (A.L.M.T. co.
  Ltd.)
• Solder Sn(80)Zn(20)
• Flux Water soluble flux

Mist sprayer
Ultrasonic wave
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TGC closing

• In order to make flat plane, the combination of
  the vacuum-press and the suction plate technique
  have been adapted.

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Physics impact using muon spectrometer
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4 Muon final state

• H?mmmm

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2 Muon final state

• For SUSY
• H/A?mm
• L-R symmetry
• Z boson

Due to bremsstrahlung of muon at calorimeter
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Charge Identification

• Important for
• B physics
• SUSY (same charge tag)
• Extended Gauge model boson
• Z, W
• Higgs (reconstruction)

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Physics Impact of the Initial Detector

• The initial detector configuration for the first
  physics run consists of the following elements
• Magnet system
• A meaningful detector needs the full magnet
  system, 
• Furthermore the construction of the barrel toroid
  is critical for the schedule, as it will
  condition the installation for all the other
  detector components
•  
• Inner Detector
• The following components will be deferred
  (staging/upgrades)
• - Part of the Pixel system (3rd point)
• Part of the RODs
• Potentially some TRT electronics
• TRT end-cap wheels type C

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• Muon instrumentation
• The following components will be deferred
  (staging/upgrades) for the low luminosity phase
• EEL and EES MDT chambers, electronics and
  supports
• Half of the CSC chamber layers (mechanics and
  electronics)
• The following component can appear as partially
  staged item
• Part of the end-wall MDT chambers
• High Level Trigger and DAQ
• The system needs to be designed to cost in a way
  that it can be easily upgraded
• Reduced processors from Common Projects
• Shielding
• A limited part of the high-luminosity shielding
  can be deferred by about one year

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What we should know on analysis
The main impact of the initial detector
configuration is that the discovery potential
for the Higgs signal in several final states will
be degraded by about 10 (meaning that 20 more
integrated luminosity is required to
compensate) Possible penalties on the pattern
recognition performance from the less robust
tracking systems are not included in these results
(The studies are documented in ATLAS RRB-D
2001-118)
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???