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 SpectrometerATLAS: 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- cylindrical in barrel- wheels in end caps

• coverage: || < 2.7

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

CMS Muon SpectrometersCMS:A Compact Muon Solenoidal detector of LHC

Muon detector coverage: || < 2.4Magnetic 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

←ATLAS ： Troidal magnetic field

　　（ y-z view)

CMS: Solenoidal magnetic Field →

(r-φview)

6m

3m

Momentum measurement

ATLAS2.5 %@100GeV

CMS8 % @ 100GeV

How to measure Pt?

S

L

Layer1

Layer2

Layer3

B

R

Pt

BLRRs

Pt

LB

R

L

TmBRGeVPtqBRPt

22

8)

2cos(1(

3.0

2)

2sin(

2

][3.0][

Measure the transverse component to B field

22

)(

3.0

8)(23

)(23

)()(

2

312

BL

Ptx

BL

Ptx

s

x

s

s

Pt

Pt

xxxs

Position resolution(x) for each

Pt resolution depends on B, L and (x) (not R)!

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

2

)()(

BL

Ptx

Pt

Pt

Interaction of charged particle

2/sin

14

4

2

2

p

cmzZr

d

d ee

z: Charge of incident particleZ: Atomic number of material

Rutherford scattering

Z

z

An incoming particle with charge z interacts elasticallywith a target of nuclear charge Z.The cross-section for this e.m. process is

Approximation- Non-relativistic- No spins• Scattering does not lead to significant energy loss

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.)

L

Rplaneplane

0

1

X

L

p

Rutherford scattering A

ZrZZN

XeA )183log()1(41 3/12

0

2010

0

22

2 )]/(log12.01[015.0

XxX

Lx

P

X: charge

Interaction of charged particle• What is the contribution of

multiple scattering to Momentum resolution?

.!)(

1)(

)()(

0

constPt

p

Px

PtxPt

p

MS

MS

Independent of Pt

0

1045.0

)(

LXBPt

p MS

More Precisely →

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’→– Need Good position resolution

• For CP-violation and B and Top physicsTrigger 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)

Bdl

Pt

Res

olu

tio

n

Acceptance as a function of

Integrated magnetic field as a function of

Solenoid magnet (CMS)• 4 T superconducting

solenoid• 13m length• Inner diameter : 5.9m

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

Energydeposit

Create Cluster

Drift Electrons

Gasamplification

Self quanch

Reach toAnode

G.MStreamer

Energy loss of charged particle

]2

2ln

2

1[

1 22

max222

22

I

Tcm

A

zKZ

dx

dE e

][3.04 2122 cmgMeVcmrNK eeA 　

222max 2 mcT

Bethe-Bloch formula (ionizing particle):

A: mass number [g/mol] of the materialz: Charge of incident particleZ: Atomic number of material

: Density correctionI : Mean excitation energy of material I=I0Z

(Max kinetic energy, which can transferred to electron)

2

1

dx

dE

22ln dx

dE

43

Energy loss of charged particle• We should also consider

bremsstrahlung for high energy muon (>100 GeV)

Ionization

Znprim 5.1

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)

Gas Z A δ(g/cm3)Ei

(eV)

I0 (eV

)Wi

dE/dxnp

(i.p.)

/cm)

nt

(i.p.)

/cm)

(MeV cm2/g)

(keV/cm)

H2 2 28.38×10−

5 15.9 15 37 4.03 0.34 5.2 9.2

He 2 41.66×10−

4 24.5 25 41 1.94 0.32 5.9 7.8

N2 14 281.17×10−

3 16.7 16 35 1.68 1.96 10 56

O2 16 321.33×10−

3 12.8 12 31 1.69 2.26 22 73

Ne 1020.2

8.39×10−

4 21.5 22 36 1.68 1.41 12 39

Ar 1839.9

1.66×10−

3 15.7 16 26 1.47 2.4429.4

94

Kr 3683.8

3.49×10−

3 13.9 14 24 1.32 4.6 22 192

Xe 54131.3

5.49×10−

3 12.1 12 22 1.23 6.76 44 307

CO2 22 441.86×10−

3 13.7 14 33 1.62 3.01 34 91

CH4 10 166.70×10−

4 15.2 13 28 2.21 1.48 16 53

C4H1

0

34 582.42×10−

3 10.6 11 23 1.86 4.5 46 195

Properties of several gases used in proportional counters (from differentsources, see the References section). Energy loss and ion pairs (i.p.) per unitlength 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 DriftIn 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 betweenacceleration 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

Position measurement with Drift chamber

Measure arrival time of electrons at sense wire relative to a time t0.

anode

TDCStartStop

DELAYscintillator

drift

low field region drift

high field region gas amplification

dttvx D )(

Gas amplificationdx

n

dnTownsend avalanche:

: first townsend coefficientE/p > 10^4/cm

xenxn )0()(

If we neglect the space-charge effect and photoelectriceffect by de-excitation of molecule, total charge (Q) = n0eM

):)/ln(

()(

)/ln(

)()(ln

)(

)(

)(

)(

lcylindricaabr

VE

E

dE

E

E

ab

V

dEdE

drEdrrM

rE

aE

rE

aE

r

a

M (gas amplification factor) is written as a function of a: radius of wire)

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 aquencherAbsorption of photons in a large energyRange. Energy dissipation by collisions or dissociation into smaller molecules.

⇔ penning effect

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

Difference between G.M and Streamer

+++

+ +

- -- -- -

-

E

+++

+ +

- -- -- -

-

E

G.M mode Large output signalLong dead time Long term stability

Streamer modeLarge output signalShort dead timeLarge discharge sometime occurLimited mean free path of photon

HV dependence of Output charge (ex.RPC)

Limited proportional

Proportional

Streamer

Monitored Drift Tube (ATLAS)

End Cap

Barrel• 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

MDT (Layout)

Number of MDT : 1194Number of Channels: 370000Area: 5500 m2

BIS

BMS

BOS

BIL

BML

BOL

Monitored Drift Tube (ATLAS)

a= 25 μmb= 30mmgas: Ar:CO2 (93:7)

tube wall: 0.4 mm Al

30 mm diameter

wire: 50 µm W-Re endplug

Position resolution: 50 µm monitoring of high mechanical precision during production

MDT (Wire Positions with a X-Ray Method)

accuracy of wire position measurement: 3 µm

measurement of the intensity as function of the motor position

average wire positioning accuracy:15 µm

selected chambers tested: 74 of 650 chambers produced at 13 sites scanned so far

X-tomograph at CERN

mechanical precision measuredwith X-ray method

goals:

• check functionality of all tubes and electronics channels

• measurement of wire positions

e.g. Test Facility at the University of Munich

• deviations from nominal positions compared to X-ray results: rmsy = 25 µm, rmsz = 9 µm

z

y

MDT (Cosmic ray test)

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

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)

• 50m 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)

32 four-layer chambers2.0 < |h| < 2.7|Z| ~ 7m, 1 < r < 2 m4 gas gaps per chamber31,000 channelsGas Ar:CO2:CF4 (30:50:20)High voltage :3.2 kV

S = d = 2.54 mmW = 5.6 mm

• Multiwire proportional chambers determine muon position by interpolating the charge on 3 to 5 adjacent strips

• Precision (x-) strip pitch ~ 5mm• Spatial resolution ~ 60 m.• 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.

- 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:– Fast signal response

(<25ns)– High efficiency

(>99 %)– Radiation-proof

(~0.6C/cm)– Rate capability

(~kHz/cm2)Wire potential 3.0 kV

Gas mixture CO2 + n-pentane

(55%) (45%)

Wire diameter 50 m

ASD: Amp. Shaper Discriminator

1.4m

1.3m

TGC performance (ATLAS)

Incident angle dependenceof drift time

Efficiency map (KOBE Univ.)

Graphite spraying

FR4 Frame Gluing Wire winding

Singlet closingMaking doublet (triplet)

Paper honeycomb

4 board /day 80 boards/month

4 boards/day3 persons

2 boards /day1 person

2 TGCs /day3 persons

1 Unit/day2 persons

Mounting Read-out boards1 Unit/day3 persons

Checking quality

TGC Production Procedure

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 m

• 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 andAuto dispenser for button supportsare adopted.

Wire winding

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

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)

Mist sprayer

Ultrasonic wave

TGC closing

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

822

20 0 0 0

26112

1

10

100

1000

10000

100000

Distortion [0.1mm]

Num

ber

of

meas

ure

dpo

ints

0 1 2 3 4 5 6

Physics impact using muon spectrometer

4 Muon final state• H→

2 Muon final state• For SUSY

– H/A→

• 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 systemA 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 DetectorThe 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

Staged items Main impact expected on

Loss in significance

One pixel layer ttH ttbb ~ 8%

Outermost TRT wheels + MDT

H 4 ~ 7%

Cryostat Gap scintillators

H 4e ~ 8%

MDT A/H 2 ~ 10% for m ~ 300 GeV

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 trackingsystems are not included in these results

(The studies are documented in ATLAS RRB-D 2001-118)

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