Maria Laach Summer School
Maria Laach Abbey
9-18 September, 2015
Principles of Detection for
Particle Physics
Part 3: High-Energy
Calorimetry
Bruce A. Schumm
Santa Cruz Institute for Particle Physics
and the
University of California, Santa Cruz
High-Energy Calorimetry Introduction
Two basic types of calorimetry
• Electromagnetic
• Make use of compact, collimated showers induced by pair-production
and brehmstrahlung
• Relatively well-understood (EGS shower MC) and precise
• For incident electrons, positrons, and photons (but remember: 0 )
• Hadronic
• For hadronic particles, of course
• I longer that LRAD, so much less compact (and less precise)
• More and more, integrated into “energy flow” approach to measure jet,
rather than individual particle, properties.
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Electromagnetic Shower Development
Incoming photon pair-converts; daughter e+e- pair radiate (brehm),
leading to more pair-production
 Shower generated almost solely by pairs production and brehm
~ LRAD
Power-law
growth stops as
particle energies
degrade to
critical energy Ec
PDG
Incoming electron starts process with brehm, but same overall
shower characteristics.
 “Electromagnetic Shower”
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Transverse Shower Development (Moliere Radius)
Substance
LRAD (cm)
RM (cm)
Iron
1.76
1.76
Copper
1.43
1.44
Lead
0.56
1.6
Tungsten
0.35
0.93
Crystal Scintillators
1-2.5
2-4
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Shower Monte Carlos
Electromagnetic
• EGS (electron gamma shower) Monte Carlo
• Developed at SLAC
• Maintained at KEK and/or (?) Canada’s National Research Council
• http://rcwww.kek.jp/research/egs/
• http://www.nrc-cnrc.gc.ca/eng/solutions/advisory/egsnrc_index.html
Hadronic
•
•
•
•
GEANT (Geometry And Tracking) MC
Developed at CERN
Maintained by international GEANT collaboration
http://www.geant4.org/geant4/
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Electromagnetic Calorimetry: Types
• Total absorption, for which the entire shower is absorbed within
the active medium
• Doped “glasses” (transparent materials with significant fractions of
heavy elements
• Lead glass, CsI, lead tungstate (PbWO4), …
• Sampling, for which the shower is largely absorbed in passive
radiator material, but the shower is periodically “sampled” with
thin layers of active medium
N.B.: All hadronic calorimeters
are sampling calorimeters
(I >> LRAD)
• Lead/Liquid Argon, Iron/Scintillator, Si/W, …
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Total Absorption Calorimetry
Figure of merit: light output
Material
Deposited Energy per
Photon
Plastic Scintillator
~100 eV
Crystal Scintillator (NaI, PbWO4)
~25 eV
Crystalline Silicon
3.5 eV
2.2x2.2x23 cm
CMS Lead Tungstate crystal
with readout (avalanche
photodiode detectors)
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Electromagnetic Calorimetry: Stochastic Term
Bruce Schumm
Calorimeter Type
b (GeV) for EM Resolution
NaI
.027
PbWO4
.035
Pb Glass
.05
Pb/Liquid Argon
.075
Pb/Scintillator
.09
Iron/Gas MWPC
.23
Maria Laach 2015, Part 3: High Energy
Calorimetry
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EM Calorimetry: Energy Resolution Full Picture
Generally, energy resolution of calorimeters parametrized as
a: Electronic noise. Fixed size; relative contribution falls linearly with calorimeter
signal (i.e., with energy)
b: Stochastic term. See last slide…
c: Systematic effects, such as light collection uniformity, shower leakage, crystal
uniformity (resolution won’t go to 0 as E).
D.V. Alexsandrov et al., A High Resolution Electromagnetic Calorimeter Based on Lead-Tungstate Crystals,
Nucl. Inst. And Meth. 550, 169 (2005).
a = 0.013 GeV
b = 0.036 GeV
c = 1.1%
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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The CMS Detector (Slice)
Last component to discuss: hadronic calorimetry…
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Hadronic Calorimetry: Shower Fluctuations
Question: How accurately can we measure the energy of, say, a +? Consider two
scenarios for the first scatter, each resulting in a dominant “leading particle”:
+
+
N
Upper scenario:
• Energy remains hadronic
• Response is lower (“h”) due to
energy lost in breaking up nuclei
…
K0
p
+

0
N
…
K+
p

Lower scenario:
• Energy becomes primarily
electromagnetic
• Response is higher (“e”)
Thus, the single-particle resolution of the hadronic calorimeter is tied to the
intrinsic fluctuations of the hadronic shower
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Hadronic Calorimetry: Compensation
R. Wigmans, High Resolution Hadron
Calorimetry, Nucl. Instr. & Meth. A265, 273 (1988)
Idea: Compensation
• Heavy elements that produce neutrons upon fragmentation
• Active materials with large response to neutron absorption
• Need not be exotic – just need to pay attention (iron/scintillator in right
proportion, for example)
• ZEUS lead/scintillating-fiber “SPACAL” achieved 30%/E, approaching the
performance of some EM calorimeters.
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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The New(ish) Development: Energy Flow
What do you really want to do with your calorimeter? For example…
m = 91 GeV/c2
Z0
m = 80 GeV/c2
W
For W/Z separation (International Linear Collier Physics), need to
optimize jet energy resolution, not individual particle resolution.
What’s in a jet?
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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What’s in a Jet?
Average content of hadronic shower (according to GEANT)
Shower
Component
Particle
Species
Charged particles ,K,p,e,…
Fraction
of Energy
Ideal Detector
System
Energy
Resolution
64%
Tracking System
O(10-3)
Photons
0  
25%
EM Calorimeter
(5-10)%/E
Neutral hadrons
K0, n, …
11%
Hadronic Calorimeter
~50%/E
Goal: measure each object with subsystem best tailored to it (pions
not measured in hadronic calorimeter!)
“Energy Flow Calorimetry”
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Energy Flow Calorimetry
1. Identify EMCal deposits associated with photons; measure in
EM calorimeter and remove deposits from collection
2. Reconstruct charge tracks and measure energy of each track.
Identify associated calorimeter deposits (both EM and
Hadronic) and remove
3. Remaining deposits are from neutral hadrons. Assemble
deposits into objects (particle candidates) and measure energy
In principle, resulting jet is well measured. For example, consider
measuring the dijet mass for the following ILC reaction:
e+e-  q qbar at Ecm = 200 GeV
Bruce Schumm
Approach
Resolution (Mjj)
Ideal Compensation
9.2 GeV/c2
Ideal Energy Flow
2.6 GeV/c2
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Calorimeter Design Basic
Compensation
• Match absorber and active layers so that
• Nuclear fragments from absorber must excite active layers to an
extent that brings hadronic response up to that of EM Cal.
Energy Flow
• Hadronic Calorimeter resolution does not play critical role
• Instead, must minimize “confusion terms” that mix objects and
lead to missing or redundant energy measurements
• Highly pixelated hadronic calorimetry
“digital” calorimeter of 1 cm2 pixels, each of which reports out
simple “hit/no-hit”?
Subject of substantial R&D, especially in context of proposed ILC
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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Wrap-up
We’ve just scratched the surface and laid out general principles.
Each of the three topics could be the subject of a week’s lecture
A significant amount of R&D is underway
• Active/monolithic pixel sensors
• Precise (high resolution, low-mass) silicon strip tracking
• Digital calorimetry
• Advanced compensating calorimeters
• Novel sensor designs (edgeless, HV CMOS, …)
• Application-optimized electronic readout
• Radiation hardness
• Applications
• Gaseous tracking and TPCs…
A rewarding area of inquiry!
Bruce Schumm
Maria Laach 2015, Part 3: High Energy
Calorimetry
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