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Particle Detectors for Colliders Calorimeters. Robert S. Orr University of Toronto. Generic Detector. Layers of Detector Systems around Collision Point. R.S. Orr 2009 TRIUMF Summer Institute. Scintillators. charged particle. photons. atom molecule lattice. - PowerPoint PPT Presentation
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R.S. Orr 2009 TRIUMF Summer Institute
Layers of Detector Systems around Collision Point
Generic Detector
Scintillatorscharged particle
photons
• Charged particle passing through matter distorts
• atom• molecule• lattice
• Relaxation of distortion – light emitted
* p A p A* A A
• Emitted photon may – excite another molecule Successive excitation & emission – different λ photons
*
*
*
* *
*
B
p p
B A
C BB
C
A
A
C
C
A
each step ~ 100 ps
whole chain ~ 1 10 ns
• Very fast – good timing resolution
R.S. Orr 2009 TRIUMF Summer Institute
• Can be extremely efficient ~ 2 /dE
MeV cmdx
2 4
collection efficiency
photomultiplier efficiency
1 /10 lost 10 /
eV cm
~ 100 photoelectrons per cm.
• Spatial resolution ~ size of scintillator ~10s cm 10
Scintillating fibres
R.S. Orr 2009 TRIUMF Summer Institute
Why are scintillators transparent to emitted light?
• Stokes shift
R.S. Orr 2009 TRIUMF Summer Institute
Gain = secondary emission factor N
dkV
number of stages
771 electron x
1110
00
1
nsG mA
50 50 mV
• Fast• Low noise• High gain
Photomultiplier
R.S. Orr 2009 TRIUMF Summer Institute
Modern Photodetectors
V
photocathode
focusing electrodes
siliconsensor
electron
• Micro-channel plates• Multi-anode pm• Hybrid pm• Visible light photon counters
R.S. Orr 2009 TRIUMF Summer Institute
Electromagnetic Showers
incident 0
0E
Converts to 2 electrons 0
2e
EE
0~ 2
Each electrons will have emitted a brems photon of energy 0
4 E
E
Now have 4 particles energy 0
4
E
Number of particles after 0t 2 tN
Average energy 0
2 t
EE t
0maxmax
2 t Ct
EE EAt the critical energy
0max
ln
ln 2 cE E
t
assume this is max depth
max 0~ lnt E
0max
c
EN
E
max 0N E
~ ~ E N E
shower grows as ln E
linear energy measurement
resolution improves with energy
R.S. Orr 2009 TRIUMF Summer Institute
Monte Carlo Simulation of an EM Shower
1
0
a btt edEE
b
dt
b
a max
11.0 ln
i
at y C
b
max 0~ lnt E
Cy E E 0.5 , 0.5 iC e
Calc max ln it y C
Put b=0.5
Get a from max
1
at
b
dE
dt
R.S. Orr 2009 TRIUMF Summer Institute
Transverse Shower Profile• Shower Broadens as it develops
• Pair
• Brems
• Compton
• Multiple Coulomb
• Moliére Radius 0S
MC
ER
E
2 421.2S eE m c MeV
• Like radiation length, Moliére radius scales for different materials
• In terms of Moliére radius, shower width is roughly independent of material - 90% of energy in
• Shower Broadens as it develops
• dense central core
• spreading with depth
2 MR
R.S. Orr 2009 TRIUMF Summer Institute
Hadronic Calorimeters
• Strong (nuclear) interaction cascade• Similar to EM shower
2 1 30 35IEM had g cm A
hadronic interaction length
• Shower length
0I
hadronic calorimeternearly always sampling calorimeters
~ 5 ~ 4 @100
~ 13 ~ 10 @1
m GeV
m TeV
• Energy Resolution
• leakage of energy
• shower fluctuations
• invisible energy loss mechanisms
R.S. Orr 2009 TRIUMF Summer Institute
Hadronic Lateral Shower Profile
Fe• Hadronic shower much broader than EM
• Mean hadronic versus MCS
Tp
0
16
1.8I cm
cm
Fe
R.S. Orr 2009 TRIUMF Summer Institute
Lateral Scaling with Material
90% containment does not scale
core scales
R.S. Orr 2009 TRIUMF Summer Institute
Calorimeter Energy Resolution
22 22
20 312 4ln
A A NAA E A
E EE E
0A
Esampling and shower fluctuations
EN
E
number of samplesenergy
energy deposited in a sampling step
E N E N E
E EN
E E
E E
E E
stochastic term 0 ~A E
R.S. Orr 2009 TRIUMF Summer Institute
Calorimeter Energy Resolution
22 22
20 312 4ln
A A NAA E A
E EE E
counting statics in sensor system
this term is usually negligible
1A
E
e.g. # of photo-electrons in PM, ion pairs in liquid argon
mean # of photo-electrons in PM per unit of incident energy
N n E
NE
N n E
n n n
1 1E
E n E
1
1A
n
2A shower leakage fluctuations – make calorimeter as deep as $$ allow
R.S. Orr 2009 TRIUMF Summer Institute
Calorimeter Energy Resolution
22 22
20 312 4ln
A A NAA E A
E EE E
noise - detector or electronics
increases with number of channels summed over
- important for low level signal- liquid argon electronics- detector capacitance
N channels with some intrinsic noise
3A
N E noise (energy)
E EN
E E
deposited energy1
Ebehaviour
3A E N
R.S. Orr 2009 TRIUMF Summer Institute
Calorimeter Energy Resolution
22 22
20 312 4ln
A A NAA E A
E EE E
inter - calibration uncertainty of channels
constant
- constant in E
• spatial in-homogeneity of detector energy response
4A
• fractional channel to channel gain uncertainty
• dead space
• temperature variation
• radiation damage
• all these influence spatial variation of effective energy response
E
k E
kE
R.S. Orr 2009 TRIUMF Summer Institute
Layers of Detector Systems around Collision Point
Generic Detector
R.S. Orr 2009 TRIUMF Summer Institute
Semi-empirical model of hadron shower development
radiation length
hadronic part
11
1E Hx
E
y
INC INCH
dEE E
dS
y eC
Cx e
electromagnetic part
0
0
0
E
H
S Sx
S Sy
interaction length
0.62 0.32ln
0.91 0.02ln
0.22
0.46
H E
H
E
E
E
C
0 0S - significant amount of material in front of calorimeter (magnet coil etc.)
R.S. Orr 2009 TRIUMF Summer Institute
More Rules of Thumb for the Hobbyist
• Shower maximum
max ~ 0.2 ln 0.7t E GeV
• 95% Longitudinal containment
95% max~ 2.5 ATTL t
0.13
ATT E GeV
• 95% Lateral containment
95% ~ 1R
• Mixtures in sampling calorimeters
active + passive material
0
0
0
1 ii
ieff
actact
act pass
crit criteff i
i iieff
crit actvis act
act critinc eff eff
f
mf
m m
f
Ef
E
R.S. Orr 2009 TRIUMF Summer Institute
Typical Calorimeter Resolutions
• Homogeneous EM (crystal, glass)
CLEO, Crystal Ball, Belle, CMS.....
0.5% 3.0%0.5%
E E
• Sampling EM (Pb/Scint, Pb/LAr)8% 15%
1%E E
CDF, ZEUS, ALEPH, ATLAS.....
• Non-compensating HAD (Fe/Scint, Fe/LAr)70% 110%
5%E E
CDF,ATLAS,H1, LEP = everyone
• Compensating HAD (DU/Scint)35%
1%E
ZEUS, HELIOS
R.S. Orr 2009 TRIUMF Summer Institute
Effect of e/h on Energy Resolution
Fe/Scint
DU/Scint
E E constE
Resolution tail
R.S. Orr 2009 TRIUMF Summer Institute
Weighting to Correct for e/h
Energy resolution does not improve
1
E1
e
h
Weight down EM part of shower
1e
h
' 1k k kE E c E
tune
R.S. Orr 2009 TRIUMF Summer Institute
Jet Energy Resolution
Fluctuations between EM and Hadronic component in jets will degrade the energy resolution for jets
Jet-jet Mass Resolution
Effects other than e/h dominate the 2-jet mass resoluton
R.S. Orr 2009 TRIUMF Summer Institute
Layers of Detector Systems around Collision Point
Generic Detector
LAr Calorimetry
SM Higgs Discovery Potential
• Five different detector technologies• Calorimetry coverage to
η 5
EM Calorimeter
WW FusionTag jets in Forward Cal
H
EM Calorimeter4H l
Hadronic & ForwardCalorimeters
&H ZZ H WW
Design Goals Technology
• EM Calorimeters ( ) and Presampler ( )
• Hadronic Endcap ( )
• Forward Calorimeter ( )
2.30 8.10
GeVmm 8
GeVmrad 40
GeV27.0
%7.0GeV%10
EEEEE r
%10
GeV%100
jets%3GeV%50
EEE
%10GeV
%100jets
EE
2.35.1
3 5
LAr Calorimeter Technology Overview
Lead/Copper-Kapton/Liquid Argon Accordion Structure
Copper/Copper-Kapton/Liquid Argon Plate Structure
Tungsten/Copper/Liquid Argon Paraxial Rod Structure
LAr and Tile CalorimetersTile barrel Tile extended barrel
LAr forward calorimeter (FCAL)
LAr hadronic end-cap (HEC)
LAr EM end-cap (EMEC)
LAr EM barrel
R.S. Orr 2009 TRIUMF Summer Institute
Electromagnetic Barrel
0 1.4
Barrel Module Schematicwith presampler
• 64 gaps /module
• 2.1 mm gap
• 2x3100 mm long
Half Barrel Assembly
• 2x16 modules
• I.R/O.R 1470/2000 mm
• 22 - 33
• 3 longitudinal samples
•
• presampler
0X
0.025 0.025 1.8
R.S. Orr 2009 TRIUMF Summer Institute
Electromagnetic Endcap1.4 3.2
• 96 gaps /module outer wheel 32 gaps/module inner wheel
• 2.8 - 0.9 mm gap outer 3.1-1.8 mm inner
• 2x8 modules
• Diam. 4000 mm
• 22 - 37
• 3 longitudinal samples
•
• Front sampling of 6
for , - strips.
0X
0.025 0.025
0X2.5
2.5 0.1 0.1
R.S. Orr 2009 TRIUMF Summer Institute
Accordion Structure
Pb Absorber
• Honeycomb spacer &• Cu/Kapton electrode
Hadronic Endcap Calorimeter (HEC)
Composed of 2 wheels per endFront wheel: 67 t 25 mm Cu platesBack wheel: 90 t 50 mm Cu plates
Rear Wheel
Wheel Assembly
Front Wheel
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