Transcript Lecture_4_Draft_3.ppt

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
• 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
p   A  p   A*
A*  B  A  B*
B C C  B
*
*
C*  C  
each step ~ 100 ps
whole chain ~ 1  10 ns
• Very fast – good timing resolution
• Can be extremely efficient
dE
~ 2 MeV / cm
dx
1 /102 eV lost  104  / cm
 collection efficiency
 photomultiplier efficiency
~ 100 photoelectrons per cm.
• Spatial resolution ~ size of scintillator ~10s cm
10 
Scintillating fibres
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Why are scintillators transparent to emitted light?
• Stokes shift
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Wavelength Shifting
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Photomultiplier
Gain =  secondary emission factor  
N
  kVd
number of stages
G 10
7
1 electron x 107
 1 mA
10ns
50  50mV
• Fast
• Low noise
• High gain
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PM Sensitivity
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Modern Photodetectors
•
•
•
•
Micro-channel plates
Multi-anode pm
Hybrid pm
Visible light photon counters
photocathode
electron
focusing
electrodes
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silicon
sensor
V
Electromagnetic Showers
Number of particles after t   0
Average energy E  t  
At the critical energy
N  2t
E0
2t
Et  max  
E0
2t max
 EC
assume this is max depth
incident 
0
E0
N max 
Converts to 2 electrons Ee 
~ 20
E0
2
Each electrons will have emitted E
a brems photon of energy E  0
4
E
Now have 4 particles energy 0
4
E0
Ec
tmax 
ln  E0 Ec 
ln 2
tmax ~ ln E0
shower grows as ln E
N max  E0
linear energy measurement
E ~ N ~ E
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resolution improves with
energy
Monte Carlo Simulation of an EM Shower
b  bt  e  bt
dE
 E0
dt
 a
tmax ~ ln E0
a 1
tmax 
a 1
 1.0  ln y  Ci 
b
y  E EC
Ci  0.5  e  , 0.5  
Calc tmax   ln y  Ci 
Put b=0.5
Get a from tmax 
dE
dt
a 1
b
“b” is sort of material independent
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Transverse Shower Profile
• Shower Broadens as it develops
• Pair
• Brems
• Compton
• Multiple Coulomb
• Shower Broadens as it develops
• dense central core
• spreading with depth
• Moliére Radius
E
RM   0 S
EC
ES  me c 2
4

 21.2 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 2  RM
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Comparison of Hadronic & Electromagnetic Showers
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Hadronic Calorimeters
• Strong (nuclear) interaction cascade
• Similar to EM shower
0  EM   I  had   35 g cm2 A1 3
hadronic interaction length
I   0
hadronic calorimeter
nearly always sampling calorimeters
• Shower length
~ 5 ~ 4m @100 GeV
~ 13 ~ 10m @1TeV
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• Energy Resolution
• shower fluctuations
• leakage of energy
• invisible energy loss
mechanisms
Sampling Calorimeter
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Hadronic Lateral Shower Profile
• Hadronic shower much broader than EM
Fe
• Mean hadronic pT
versus MCS
Fe
I 16 cm
 0 1.8 cm
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Hadronic Shower Longitudinal Development
ZEUS
Uranium/Scint
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Lateral Scaling with Material
90% containment
does not scale
core scales
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Calorimeter Energy Resolution
 A3 N
2
    A0   A1 

  A2 ln E   
  


E  E   E 
 E
2
2
A0
E
2
2

  A4

sampling and shower fluctuations
number of samples
energy
E
N
E
energy deposited in a sampling step
 E   N  E  N  E
E
E
E
E
 N

E
E
E
E
stochastic term A0 ~ E
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Calorimeter Energy Resolution
 A3 N
2
    A0   A1 

  A2 ln E   
  


E  E   E 
 E
2
2
A1
E
2
counting statics in sensor system
N  nE
E 
E
E

N
n

2

  A4

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

n
n
1
1

n
E
A1 
1
n
this term is usually negligible
A2 shower leakage fluctuations – make calorimeter as deep as $$ allow
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Calorimeter Energy Resolution
 A3 N
2
    A0   A1 

  A2 ln E   
  


E  E   E 
 E
2
2
2
2

  A4

A3 noise - detector or electronics - important for low level signal
- liquid argon electronics
- detector capacitance
N channels with some intrinsic noise   N  E
E
E
N
E
E
noise (energy)
deposited energy
1
behaviour
E
A3
E  N increases with number of channels summed over
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Calorimeter Energy Resolution
 A3 N
2
    A0   A1 

  A2 ln E   
  


E  E   E 
 E
2
2
2
A4 inter - calibration uncertainty of channels
2

  A4

- constant in E
• fractional channel to channel gain uncertainty
• spatial in-homogeneity of detector energy response
• dead space
• temperature variation
• radiation damage
• all these influence spatial variation of effective energy response
  kE
E
E
 k constant
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Calorimeter non-uniformity
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Generic Detector

Layers of Detector Systems around Collision Point
R.S. Orr 2009 TRIUMF Summer Institute
Semi-empirical model of hadron shower development
 Cx E 1 e x 
 y  H 1 e y 
dE
 EINC 
  EINC 1  C  

dS
   E  
   H  
hadronic part
electromagnetic part
S  S0 

x  E
0
S  S0 

y  H

S0  0
radiation length
interaction length
 H   E  0.62  0.32 ln E
 H  0.91  0.02 ln E
 E  0.22
C  0.46
- significant amount of material in front of calorimeter
(magnet coil etc.)
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More Rules of Thumb for the Hobbyist
• Mixtures in sampling calorimeters
• Shower maximum
active + passive material
tmax    ~ 0.2ln E  GeV   0.7
1
 eff
• 95% Longitudinal containment
L95%    ~ tmax  2.5ATT
ATT    E  GeV  
• 95% Lateral containment
R95% ~ 1
f act
0.13

i
fi
 0i
mact

mact  m pass
 effcrit
 icrit
  fi i
 eff
0
i
crit
Evis
 act
 0act
 f act crit
Einc
 eff  eff
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Typical Calorimeter Resolutions
0.5%
3.0%

 0.5%
E
E
• Homogeneous EM (crystal, glass)
CLEO, Crystal Ball, Belle, CMS.....
• 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
35%
 1%
E
• Compensating HAD (DU/Scint)
ZEUS, HELIOS
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Invisible Energy in Hadronic Showers
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Difference in Response to Electrons and Hadrons
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Effect of e/h on Energy Resolution
Resolution tail
Fe/Scint
E
E  const
E
DU/Scint
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Effect of e/h on Linearity
Fe/Scint
DU/Scint
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Weighting to Correct for e/h
Energy resolution does not improve
e
1
1
h
E
e
1
h
Weight down EM part of shower
Ek'  Ek 1  c  Ek 
tune
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Jet Energy Resolution
Jet-jet Mass Resolution
Fluctuations between EM and
Hadronic component in jets will
degrade the energy resolution for jets
Effects other than
e/h dominate the 2jet mass resoluton
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Jet-Jet Mass Resolutions
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Conceptual Readout Schemes
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ZEUS Forward Calorimeter
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Generic Detector

Layers of Detector Systems around Collision Point
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LAr Calorimetry
• Five different detector technologies
• Calorimetry coverage to
η 5
SM Higgs Discovery Potential
H  4l
EM Calorimeter
H  
EM Calorimeter
WW Fusion
Tag jets in Forward Cal
H  ZZ
&
H  WW
Hadronic & Forward
Calorimeters
LAr Calorimeter Technology Overview
Design Goals
Technology
• EM Calorimeters (0    3.2 ) and Presampler ( 0    1.8 )

10%
0.27

 0.7% 
E
E GeV 
E GeV 
 
40 mrad
E GeV 
 r 
8 mm
E GeV 
Lead/Copper-Kapton/Liquid Argon Accordion Structure
• Hadronic Endcap (1.5    3.2 )
50%

100%
 3%   jets  
 10%
E GeV 
E
E GeV 
Copper/Copper-Kapton/Liquid Argon Plate Structure
• Forward Calorimeter (3    5 )

 jets   100%  10%
E
E GeV 
Tungsten/Copper/Liquid Argon Paraxial Rod Structure
LAr and Tile Calorimeters
Tile barrel
Tile extended barrel
LAr hadronic
end-cap (HEC)
LAr EM end-cap (EMEC)
LAr EM barrel
LAr forward calorimeter (FCAL)
Electromagnetic Barrel
0    1.4
Barrel Module Schematic
with 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 X 0
• 3 longitudinal samples
•    0.025  0.025
• presampler   1.8
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Electromagnetic Endcap
1.4    3.2
• 2x8 modules
• Diam. 4000 mm
• 22 - 37
X0
• 3 longitudinal samples
• 96 gaps /module outer wheel
32 gaps/module inner wheel
•
• 2.8 - 0.9 mm gap outer
3.1-1.8 mm
inner
• Front sampling of 6
  
0.025  0.025
  2.5  0.1 0.1
X0
for   2.5,  - strips.
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Accordion Structure
Pb Absorber
• Honeycomb spacer
&
• Cu/Kapton electrode
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Prototype of EM endcap
Detail of Kaptons
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ATLAS FCAL
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Pictures of assembly process
LAr Forward Calorimeters
• FCAL C assembly into tube – Fall 2003
ATLAS HEC Structure
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Hadronic Endcap Calorimeter (HEC)
Front Wheel
Rear Wheel
Wheel Assembly
Composed of 2 wheels per end
Front wheel: 67 t 25 mm Cu plates
Back wheel: 90 t 50 mm Cu plates
Oct 2002
Electromagnetic Endcap
Hadronic Endcap
HEC – FCAL Assembly
Lar Endcap Installed in ATLAS