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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
– http://cmsdoc.cern.ch/cms/TDR/MUON/muon.html
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
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 to minimise the
multiple scattering
• 3 detector stations
Trackers:
- cylindrical in barrel
• fast trigger chambers: TGC, RPC
- wheels in end caps
• high resolution tracking detectors:
MDT,CSC
• coverage: || < 2.7
CMS Muon Spectrometers
CMS:A Compact Muon Solenoidal detector of LHC
Muon detector coverage: || < 2.4
Magnetic Field =4 Tesla
Difference of 2 type magnetic fields
*Large Homogenous field inside coil
*Weak opposite field in return yoke
*Size limited
*Large size area with high magnetic field
*Non-uniform field
*Field always perpendicular to momentum
6m
←ATLAS：Troidal magnetic field
（y-z view)
3m
CMS: Solenoidal magnetic
Field →
(r-φview)
Momentum measurement
ATLAS
2.5 %@100GeV
CMS
8 % @ 100GeV
How to measure Pt?
Measure the transverse component to B field
L
Pt  qBR  Pt[GeV ]  0.3BR[Tm]
L
 
0.3LB
 sin( )    
2R
2
2
Pt

 2 L2 B
s  R(1  cos( )  R
2
8 Pt
B
S
L ayer
1
L ayer
2

R
L ayer
3
Position resolution (x) for each
s  x2 
 ( Pt )
Pt

x1  x3
2
 ( s)
s

3
 ( x)
2

s
3
 ( x)  8Pt
 ( x)  Pt
2

0.3  BL2
BL2
Pt resolution depends on B, L and (x) (not R)!
Important parameters for Pt
 ( Pt )
Pt

 ( x)  Pt
2
BL
• 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
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
2
m c
d
1
 4 zZre2  e 
4
d

p
sin
 /2


z: Charge of incident particle
Z: Atomic number of material
z
Approximation
- Non-relativistic
- No spins
• Scattering does not lead to significant energy loss
Z
Interaction of charged particle
•
•
Multiple scattering (Moliere formula)
– Approximates the projected
scattering angle of multiple
scattering by a Gaussian, with a
width
2 2


0
.
015
x L

 2  
[1  0.12 log 10 ( x / X 0 )]2
 P  X 0
Approximation

1
p
X: charge
L
X0
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.)
4N A Z ( Z  1)re2 log( 183Z 1/ 3 )
1

Rutherford scattering
X0
A
L
plane
Rplane
Interaction of charged particle
•
What is the contribution of
multiple scattering to
Momentum resolution?
 ( p)
Pt
 ( x)

  ( x)  Pt
MS
1
 0 
P
 ( p)
Pt
MS
 const .!
Independent of Pt
More Precisely →
 ( p)
Pt
MS
1
 0.045
B LX 0
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
Toroid magnet (ATLAS)
• Current=20.5kA
• 25.3 m length
• 4 T on superconductor
Magnetic field and Pt resolution (ATLAS)
Integrated magnetic field as a function of 
Acceptance as a function of 
Pt Resolution
 Bdl


Solenoid magnet (CMS)
• 4 T superconducting
solenoid
• 13m length
• Inner diameter : 5.9m
Magnetic field and Pt resolution (CMS)
Integrated magnetic field as a function of 
Acceptance as a function of 
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!)
How to read the signal?
Incident charged
particle
Energy
deposit
Create Cluster
Drift Electrons
Gas
amplification
Re ac h t o
An o de
Self quanch
G.M
Streamer
Energy loss of charged particle
Bethe-Bloch formula (ionizing particle):
dE
1 2me c 2  2 2Tmax

2 z 1
2
  KZ
[
ln



]
dx
A 2 2
I2
2
K  4N A re2 me c 2  0.3[ MeV　 g 1cm 2 ]
Tmax  2mc2  2 2
(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
dE
1
 2
dx

: Density correction
I : Mean excitation energy of material
I=I0Z
  3  4
dE
 ln  2 2
dx
Energy loss of charged particle
• We should also consider
bremsstrahlung for high energy
muon (>100 GeV)
Ionization
Incident particle interact with gas
molecule, then producing electron and
ion pairs (nprim).
nprim has relationship with average Z
of gas molecule
n prim  1.5Z
This primary electrons are energetic
enough to ionize other molecule
(secondary : ns ~3)
dE/dx
I0
(eV)
Wi
(MeV
cm2/g)
(keV/cm)
np
(i.p.)
/cm)
nt
(i.p.)
/cm)
Gas
Z
A
δ(g/cm3)
Ei
(eV)
H2
2
2
8.38×10−5
15.9
15
37
4.03
0.34
5.2
9.2
He
2
4
1.66×10−4
24.5
25
41
1.94
0.32
5.9
7.8
N2
14
28
1.17×10−3
16.7
16
35
1.68
1.96
10
56
O2
16
32
1.33×10−3
12.8
12
31
1.69
2.26
22
73
Ne
10
20.2
8.39×10−4
21.5
22
36
1.68
1.41
12
39
Ar
18
39.9
1.66×10−3
15.7
16
26
1.47
2.44
29.4
94
Kr
36
83.8
3.49×10−3
13.9
14
24
1.32
4.6
22
192
Xe
54
131.
3
5.49×10−3
12.1
12
22
1.23
6.76
44
307
CO2
22
44
1.86×10−3
13.7
14
33
1.62
3.01
34
91
CH4
10
16
6.70×10−4
15.2
13
28
2.21
1.48
16
53
C4H10
34
58
2.42×10−3
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
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
Electron Drift
In the absence of electric fields
electron –ion pairs recombine and the
net liberated charges disappear.
MWPC
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.
Cylindrical
Position measurement with Drift
chamber
DELAY
Stop
TDC
Start
scintillator
Measure arrival time of
electrons at sense wire
relative to a time t0.
drift
low field region
drift
anode x   vD (t )dt
high field region
gas amplification
Gas amplification
dn
   dx
Townsend avalanche:
n
: first townsend coefficient
E/p > 10^4/cm
 n( x)  n(0)ex
If we neglect the space-charge effect and photoelectric
effect by de-excitation of molecule, total charge (Q) = n0eM
M (gas amplification factor) is written as a function of 
(a: radiusrof wire) E ( r )
ln M    (r )dr 
a

 (E)
E (a)
dr
dE
dE
V
 ( E ) dE
V


(
E

: cylindrica l )

ln( b / a) E ( a ) E E
r ln( b / a)
E (r )
Induced signal is written as
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
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)
+
++
+ +

E
+
++
+ +
-
- ---
G.M mode
Large output signal
Long dead time
Long term stability
-
E
Difference between G.M and
Streamer
- ---
Streamer mode
Large output signal
Short dead time
Large discharge sometime occur
Limited mean free path of photon
HV dependence of Output charge
(ex.RPC)
Streamer
Limited proportional
Proportional
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: 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
MDT (Layout)
BOL
BOS
BML
BIL
BIS
BMS
Number of MDT : 1194
Number of Channels: 370000
Area: 5500 m2
Monitored Drift Tube (ATLAS)
Position resolution: 50 µm
 monitoring of high mechanical
precision during production
a= 25 μm
b= 30mm
gas: Ar:CO2 (93:7)
tube wall: 0.4 mm Al
30 mm diameter
endplug
MDT (Wire Positions with a X-Ray Method)
X-tomograph
at CERN
measurement of the intensity as
function of the motor position
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
MDT (Cosmic ray test)
goals:
e.g. Test Facility at the University of Munich
• check functionality of all
tubes and electronics channels
• measurement of wire positions
y
z
• deviations from nominal positions compared
to X-ray results: rmsy = 25 µm, rmsz = 9 µm
MDT (Tracking efficiency)
track-reconstruction efficiency
total track-reconstruction efficiency:
• ( 99.97 +0.03
- 0.9 )% without irradiation
• ( 99.77 +0.23
- 0.8 )% at highest ATLAS rate
(for 4m long tubes)
 even at highest expected irradiation
no deterioration of track-reconstruction efficiency
Drift Tube (CMS)
• Gas : Ar(85) + CO2(15)
• HV = 3.6 kV
• Spatial Resolution: 100μm
– (Single cell space resolution :
< 250μm)
Drift Tube (Layout: CMS)
Drift Tube (CMS)
HV=3600 V
cm
Drift Tube
(Tracking efficiency :CMS)
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
CSC (ATLAS,CMS)
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
•
•
•
•
•
•
Multiwire proportional chambers determine muon position by
interpolating the charge on 3 to 5 adjacent strips
Precision (x-) strip pitch ~ 5mm
Spatial resolution  ~ 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.
Resistive Plate Chamber
(ATLAS,CMS)
• gas: C2H2F4:isoC4H10
(97:3)
• 2mm gas gap
• HV=9kV
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.
Thin Gap Chamber (ATLAS)
Requirements on
ATLAS:
ASD: Amp. Shaper Discriminator
Wire potential
3.0 kV
Gas mixture
CO2 + n-pentane
(55%) (45%)
Wire diameter
50 mm
– Fast signal response
(<25ns)
– High efficiency
(>99 %)
– Radiation-proof
(~0.6C/cm)
– Rate capability
(~kHz/cm2)
1.3m
1.4m
TGC performance (ATLAS)
Efficiency map (KOBE Univ.)
Incident angle dependence
of drift time
TGC Production Procedure
Checking quality
Graphite spraying
80 boards/month
4 board /day
FR4 Frame Gluing
4 boards/day
3 persons
Mounting
Read-out boards
1 Unit/day
3 persons
Wire winding
2 boards /day
1 person
Making doublet (triplet)
Singlet closing
2 TGCs /day
3 persons
1 Unit/day
2 persons
Paper honeycomb
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 -ray
radioactive source
 Cosmic ray test at KOBE Univ.
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.
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.
Mist sprayer
 Total ~ 800,000 wires
Anode Wire: Gold plated Tungsten
(A.L.M.T. co. Ltd.)
Solder: Sn(80)+Zn(20)
•
Flux: Water soluble flux
Ultrasonic wave
TGC closing
Number of measured
points
•
100000
In order to make flat plane,
the combination of the
vacuum-press and the
suction plate technique have
been adapted.
26112
10000
822
1000
100
10
1
2
0
1
2
0
3
0
4
0
5
Distortion [0.1mm]
0
6
Physics impact using muon
spectrometer
4 Muon final state
• H→mmmm
2 Muon final state
• For SUSY
– H/A→mm
• L-R symmetry
– Z’ boson
Due to bremsstrahlung of
muon at calorimeter
Charge Identification
• Important for
– B physics
– SUSY (same charge tag)
– Extended Gauge model boson
• Z’, W’
– Higgs (reconstruction)
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
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
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
Staged items
One pixel layer
Main impact
expected on
ttH  ttbb
Loss in significance
~ 8%
Outermost TRT
wheels + MDT
H  4m
~ 7%
Cryostat Gap
scintillators
MDT
H  4e
~ 8%
A/H  2m
(The studies are documented in ATLAS RRB-D 2001-118)
~ 10%
for m ~ 300 GeV
おわり