D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 1
Introduction to Calorimetry David Cockerill RAL, UK & CMS
Marie Curie, GSI 21 March 2012
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 2
Overview
• Introduction
• Electromagnetic Calorimetry
* particle interactions
* energy resolution
• Hadronic Calorimetry
* particle interactions
* energy resolution
• Jets and Particle Flow
• Homogeneous and Sampling calorimeters
• Future directions in calorimetry
• Calorimeters at work
• Summary
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Introduction to Calorimetry 21.3.2012 3
Calorimetry - one of the most important and powerful detector techniques in
experimental particle physics
* Measurement of particle energy by total absorption in the calorimeter
* Measurement of the spatial location of the energy deposit, the angle (sometimes),
and timing: important for triggers and collision tagging
* Convert energy E of the incident particle into a detector response S
Basic mechanism: formation of electromagnetic or hadronic cascades/showers
* Compact detectors, cascade length increases only as log(E)
* Energy resolution improves with increasing E, unlike spectrometers
* Can provide fast response, to avoid pileup, for triggering
Introduction
Particle,
energy E
Signal, S
Particle cascade/shower
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Introduction to Calorimetry 21.3.2012 4
Introduction
Calorimetry
The detectors fall into two main categories:
Electromagnetic calorimeters for the detection of
e and neutral particles (o)
Hadron calorimeters for the detection of
, p, K and neutral particles n, K0L
usually traverse the calorimeters, only losing small amounts of energy by ionisation
* These 13 particles completely dominate the types of particles from high energy collisions
likely to reach and interact with the calorimeters
* All other particles decay ~instantly, or in flight, usually within a few hundred microns from the
collision, into one or more of the particles above
* Neutrinos, υ, and neutralinos, χo ,undetected, but with hermetic calorimetry can be inferred
from measurements of missing transverse energy in collider experiments
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Introduction to Calorimetry 21.3.2012 5
Introduction
Look at a wedge of CMS, at the LHC, to show the typical layout of
the Tracker, the Calorimeters and Muon detectors
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Introduction to Calorimetry 21.3.2012 6
Introduction
Sign of particle charge from the tracker
Tracker - minimum material to avoid losing
particle energy before the calorimeters
em had
Tracker calorim calorim
e
p, ,K
n, K0
Neutral
Neutral
Magnetic
field, 4T
μ
CMS: Particle identification from:
* Deposited energy location - in ECAL or HCAL
* Presence or absence of corresponding tracks in the Tracker
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Introduction to Calorimetry 21.3.2012 7
Electromagnetic Calorimetry
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Introduction to Calorimetry 21.3.2012 8
Energy losses by electrons and photons
In matter, electrons and photons loose energy interacting with nuclei and atomic electrons
• electrons/ bremsstrahlung (nucleus)
positrons ionisation (atomic electrons)
• photons pair production (nucleus),
(above 1 GeV)
compton scattering (atomic electrons)
photoelectric effect (atomic electrons)
Above 1 GeV, radiative processes dominate energy loss by e/
The processes lead to an e.m. cascade or shower of particles
eventually dissipating its energy in the calorimeter by ionisation and absorption
In the following, use the crystal PbWO4, and/or Pb, to illustrate cascade properties.
Electromagnetic cascades (showers)
Z,A
Z
e+
e-
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Introduction to Calorimetry 21.3.2012 9
Favours the use of high Z materials
for a compact e.m. calorimeter
31
31
183ln4
183ln4
220
0
22
ZrZN
AX
X
E
dx
dE
ZEr
A
ZN
dx
dE
eA
eA
Electrons
Z,A
Bremsstrahlung, main loss for electrons/positrons above O(10 MeV)
Characterised by a ‘radiation length’, Xo, in the absorbing medium
over which an electron loses, on average, 63.2% of its energy
by bremsstrahlung.
2
2
m
EZ
dx
dE
0/
0
XxeEE
X0 ~ 180 A/Z2 [g cm-2] In Pb, Z = 82, A = 207 X0 ~ 5.6 mm
Electrons continuously loose energy by ionising the medium.
Eventually, as they drop below O(10 MeV), this becomes the main loss. This transition
is at a critical energy, Ec. Finally, the electrons range out and stop.
where
e
1/me2 dependence
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Introduction to Calorimetry 21.3.2012 10
Muons
Z,A
Why don’t muons also loose all their energy in the calorimeters ??
2
2
m
EZ
dx
dE
0/
0
XxeEE
mµ = 210 me
Muons emit significant bremsstrahlung
only above ~1 TeV
Muons loose only (O) GeV in the
calorimeters by ionisation, so high energy
muons pass through the calorimeters.
where
µ
Bremstrahlung: 1/m2 dependence
µ
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Introduction to Calorimetry 21.3.2012 11
Below ~ 5 MeV in PbWO4, Compton scattering dominates (blue line), with an
electron ejected at each scattering site.
Below ~ 0.5 MeV in PbWO4, the photo-electric effect dominates (green dashed)
and the photon path finishes with the production of an electron.
Photons
Z
e+
e-
Pair production, main loss for photons above 1 GeV
Characteristic mean free path before pair production, λpair = 9/7 Xo
Intensity of a photon beam entering calorimeter reduced to 1/e of
the original intensity, I = Io exp(-7/9 x/Xo). λpair = 7.2 mm in Pb
22 cmE e
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05m
ass a
tte
nu
atio
n c
oe
ffic
ien
t (g
/sq
cm
)
photon energy (MeV)
PbWO4
Total
Compton scattering
Photoelectric effect
Pair production
10-1 10-0 101 102 103 104 105
photon energy (MeV)
101
100
10-1
10-2
10-3
10-4
mas
s at
ten
uat
ion
co
effi
cien
t (g
-1cm
2 )
PbWO4 Flat
with
energy
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Introduction to Calorimetry 21.3.2012 12
Brem and pair production dominate the processes that degrade the
incoming particle energy
50 GeV electron
Loses 32 GeV over 1 X0 by bremsstrahlung
50 GeV photon
Pair production to e+ e- , 25 GeV to each particle
Energy regime degraded by 25 GeV
Minimum ionising particle (m.i.p)
In Pb, over 1 X0, ionization loss ~O(10s) of MeV
Factor of ~1000 less than the radiative losses.
Electromagnetic Cascades
Z,A
Z
e+
e-
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Introduction to Calorimetry 21.3.2012 13
Below a certain energy, defined as Ec,
e± energy losses, via ionisation, greater
than energy losses via bremsstrahlung
Slow decrease in number of particles in the shower
Photons progressivley lose energy by
* compton scattering
* converting to electrons via the photo-electric
effect, and absorption
Electrons/positrons range out/stop through
* ionization of the medium
* annihilation (positrons)
The multiplication process runs out
Electromagnetic Cascades
Ec
24.1
610
Z
MeVEc
For Pb, Z=82, Ec = 7.3 MeV
Liquids and solids
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Introduction to Calorimetry 21.3.2012 14
2ln
ln 0max
cEEt
tt EparticletEtN 2/)(2)( 0
c
tt
t
tttotal
E
EN 0
0
)1(222122 max
max
max
For a 50 GeV electron on Pb Ntotal ~ 14000 particles
tmax at ~13 Xo (an overestimate)
Process continues until E(t)/particle < Ec
This layer contains the maximum number of
particles:
EM Cascades: a simple model
Consider only Bremstrahlung and pair production Assume lpair and X0 are equal and that, after each X0, the number of particles increases by factor 2 After ‘t’ layers of X0, number of particles:
Electron shower in a cloud
chamber with lead absorbers
Ec
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Introduction to Calorimetry 21.3.2012 15
Longitudinal Shower Development
Shower grows only logarithmically with Eo
Shower maximum, where most energy deposited,
tmax ~ ln(Eo/Ec) – 0.5 for e
tmax ~ ln(Eo/Ec) + 0.5 for
tmax ~ 5Xo, 4.6 cm, for 10 GeV electrons in PbWO4
Shower profile for electrons of energy: 10, 100, 200, 300…GeV PbWO4
X0
EM Cascade Profiles
No
rmalised
en
erg
y l
oss
How many X0 to adequately contain an em shower?
Rule of thumb:
RMS spread in energy leakage at the back of the calorimeter
= 0.5 * average energy leakage at the back
CMS - want < 0.3% rms energy leakage
Require < 0.65% average energy leakage => PbWO4 25X0, 23 cm long
25 0
Simulation
20 10 tmax ~ 5Xo
Eo= 10GeV CMS barrel crystals
25X0 = 23cm
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Introduction to Calorimetry 21.3.2012 16
EM Cascade Profiles
Transverse Shower Development
Mainly multiple Coulomb scattering by e in shower
95% of shower cone located in cylinder of radius
2 RM where RM = Moliere Radius
]/[MeV21 2
0 cmgXE
Rc
M
Radius
(RM)
% o
f In
teg
rate
d e
ne
rgy
50 GeV e- in PbWO4
RM = 2.19cm in PbWO4, Xo = 0.89cm, Ec ~ 8.5MeV
Simulation
2 RM
2.19cm in
PbWO4
How many RM to adequately contain an em shower?
Lateral leakage degrades the energy resolution
An additional contribution to the stochastic term (see later)
In CMS, keep contribution to < 2%/sqrt(E)
Achieved by summing energy over 3x3 (or 5x5) arrays of PbWO4 crystals
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Introduction to Calorimetry 21.3.2012 17
EM Cascade Profiles
EM shower development in Krypton (Z=36, A=84)
GEANT simulation of a 100 GeV electron shower in the NA48 liquid Krypton calorimeter
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Introduction to Calorimetry 21.3.2012 18
Electromagnetic Energy Resolution
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Introduction to Calorimetry 21.3.2012 19
Electromagnetic Energy Resolution
Assume energy released in the detector material (mainly ionisation, excitation) is
proportional to the energy of incident particle
Mean energy required to produce a ‘visible’ photon
in a crystal or an electron-ion pair in a noble liquid Q
Mean number of quanta produced <n> = E / Q
Energy resolution is given by the fluctuations on ‘n’
σE / E = n / n = (Q / E ) also applies for hadron calorimeters
Generally :
‘Stochastic term’
given above ‘Noise term’
Electronics
Pile up
‘Constant term’ Imperfections in calorimeter construction
(dimension variations)
Non-uniform detector response
Channel to channel intercalibration errors
Fluctuations in longitudinal energy containment
Energy lost in dead material, before in detector
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Introduction to Calorimetry 21.3.2012 20
Electromagnetic Energy Resolution
Energy resolution at high energy usually dominated by the constant term, c
Relative resolution improves with Energy
Goal of calorimeter design - find best compromise between the three contributions to the
resolution
a , stochastic term = 2.83%
b , noise term = 124 MeV
c , constant term = 0.26%
An example of the (very good) energy
resolution for electrons measured using
PbWO4 crystals, CMS ECAL, test beam
Electron energy
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Introduction to Calorimetry 21.3.2012 21
However, in certain cases:
Energy of the incident particle is only transferred to making quanta,
and to no other energy dissipating processes, for example in Ge.
Stochastic fluctuations much reduced
Now σE / E = (FQ / E ) where F is the ‘Fano’ factor .
F ~ 0.1 in Germanium
Detector resolution in AGATA 0.06% for 1332keV photons
Conversely, photo-detectors can introduce more fluctuations:
For CMS PbWO4 crystals, scintillation emission small fraction of energy loss and F ~ 1
However - fluctuations in the avalanche process in the Avalanche Photodiodes used for the
photo-detection gives rise to an excess noise factor in the gain of the device
This leads to F ~ 2 for the PbWO4 + APD combination
Npe ~ 4500 photo-electrons released by APD, per GeV of deposited energy
Coefficient of stochastic term ape = F / Npe = (2 / 4500) = 2.1%
Including lateral leakage fluctuations (2%) Total estimated stochastic term 2.9%
2.8% measured
Electromagnetic Energy Resolution
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Introduction to Calorimetry 21.3.2012 22
Electromagnetic Energy Resolution
Energy [keV]
Energy [keV]
Co
unts
Co
unts
Doppler corrected using:
psa result
centre of segment
centre of detector
Doppler corrected using:
psa result
centre of segment
centre of detector
Experiment with excited nucleii from a target
An example of the ‘Fano’ factor in
action: the AGATA Ge detector
1382 keV line, width 4.8 keV (fwhm)
Resolution 0.15%
(0.06% with source)
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Introduction to Calorimetry 21.3.2012 23
Hadron Calorimeters
Hadron calorimeters
* essential to detect jets, which are fragments of
fundamental constituents such as quarks and gluons.
*Jets often comprise many (and o) and other
hadrons.
* Sometimes they may contain just a single pion.
Each of the hadrons will generate its own hadronic
cascade, which will often span both the ECAL and HCAL,
and overlap with other cascades from the jet.
The story is far more complex than for em cascades.
HCAL
ECAL
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Introduction to Calorimetry 21.3.2012 24
Hadronic Cascades
Degradation of the hadron energy into a cascade proceeds through an increasing number of
(mostly) strong complex interactions with the calorimeter material.
Two classes of effects:
* Energetic secondary hadrons are produced with a mean free path, λI ~ 35 A1/3 g/cm2
between interactions. Their momenta a ‘fair fraction’ of the primary hadron.
* A significant part of the primary energy consumed by nuclear processes:
excitation, neutron evaporation, spallation involving particles of O(MeV)
energies. Dominated by electrons positrons photons and neutrons
p, n, , K,… mbAinel 3507.0
0
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Introduction to Calorimetry 21.3.2012 25
Hadronic Cascades
p, n, , K,…
Collision with a nucleus
Multiplicity of secondary particles ln(E)
n(0) ~ ln E (GeV) – 4.6
For a 100 GeV incoming pion, n(0) 18
Further collisions and mutliplication
continue until energy of secondaries
below the threshold for pion production
Either not detected or too slow to be within
detector time window
= invisible energy
Detector response to hadronic component
smaller than it should be
Electron response > hadron response
e/h > 1
Electrons, photons -> em showers
o-> -> em showers
Charged hadrons 20%
Nuclear fragments, p 25%
Neutrons, soft 15%
Breakup of nuclei 40%
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Introduction to Calorimetry 21.3.2012 26
Signal, per GeV of hadron component (h) and
signal per GeV of electomagnetic component (e)
for a hadron calorimeter with e/h = 1.8
2 dissimilar contributions to the total detector response
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Introduction to Calorimetry 21.3.2012 27
Hadronic Cascades
Electromagnetic component fraction
Fraction is large, varies wildly, event to event
Includes - p -> o n
+ n -> o p
The average e.m. fraction increases with
incoming hadron energy:
These fluctuations in fem give rise to
* non linearity, since e/h > 1
* non gaussian response
* poor energy resolution
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Introduction to Calorimetry 21.3.2012 28
Hadronic Cascades
Unlike electromagnetic showers, hadron showers do not show a
uniform deposition of energy throughout the detector medium
p, n, , K,…
Red - e.m. component Blue – charged hadrons
Simulation of two hadron showers
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ATLAS, CALOR 2008
Tile Fe/Scintillator
tmax
Introduction to Calorimetry 21.3.2012 29
Hadronic Cascades
The e.m. component more pronounced at
start of the cascade than hadronic
component
* peak close to the first interaction
* exponential fall off with scale λI
Longitudinal profile of pion
induced showers at various energies
For Iron
a = 9.4, b=39 lI =16.7 cm
For a pion of 100 GeV, t 95% 80 cm
For adequate containment, need ~10 lI
Depth of Iron needed 1.67 m
Depth of Cu needed 1.35 m
bEacmt
GeVEt I
ln)(
7.0][ln2.0)(
%95
max l
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Introduction to Calorimetry 21.3.2012 30
Hadronic Cascades
Hadron lateral shower development
Lateral spread of shower from
transverse energy of secondaries,
<pT> ~ 350 MeV/c
Core + Halo
95% containment in a cylinder of
radius λI = 16.7cm in Fe
Compare to 2.19 cm for an
electromagnetic cascade in PbWO4
Radial shower profile for a 150 GeV pion
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Introduction to Calorimetry 21.3.2012 31
Hadronic energy resolution
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Introduction to Calorimetry 21.3.2012 32
Hadronic energy resolution
Consequences for e/h 1
- response with energy is non-linear
- fluctuations on Fπ° contribute to σE /E
Since the fluctuations are non-Gaussian,
- σE /E scales more weakly than 1/ E , more as 1/ E
- Deviations from e/h = 1 also contribute to the constant term
‘Compensating’ sampling hadron calorimeters
Retrieve e/h = 1 by compensating for the loss of invisible energy, several approaches:
Weighting energy samples with depth
Use large elastic cross section for MeV neutrons scattering off hydrogen in the organic
scintillator
Use 238U as absorber. 238U fission is exothermic. Release of additional neutrons
Neutrons liberate recoil protons in the active material
Ionising protons contribute directly to the signal
Tune absorber/scintillator thicknesses for e/h = 1
Example Zeus: 238U plates (3.3mm)/scintillator plates (2.6mm), total depth 2m, e/h = 1
Stochastic term 0.35/ E(GeV)
Dual readout, Cerenkov radiator to get only em part, scintillator – all parts
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Introduction to Calorimetry 21.3.2012 33
Hadronic Energy Resolution
Compensated hadron calorimetry & high precision
em calorimetry are usually incompatible
In CMS, hadron measurement combines
HCAL (Brass/scint) and ECAL(PbWO4) data
Effectively a hadron calorimeter divided in depth
into two compartments
Neither compartment is ‘compensating’:
e/h ~ 1.6 for ECAL
e/h ~ 1.4 for HCAL
Hadron energy resolution is degraded and
response is energy-dependent
CMS:
Stochastic term a =120% (Zeus 35%)
Constant term c = 5%
CMS energy resolution for single pions
up to 300GeV
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Introduction to Calorimetry 21.3.2012 34
Cascades – a comparison
Cascade
Electromagnetic Hadronic
X0 ~ 180 A / Z2 << λI ~ 35 A1/3
23 cm deep x 2.19 cm 80 cm deep x 16.7 cm
Electromagnetic cascades:
- well understood
- linear response with energy
- simulations succesfully reproduce observed distributions
Hadron cascades:
- much harder to model
- large, non predictable, event to event variations
- non linear response
Hadron calorimeters much larger than em calorimeters
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Introduction to Calorimetry 21.3.2012 35
Jets and Particle Flow
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Introduction to Calorimetry 21.3.2012 36
Jets and Particle Flow
At colliders, hadron calorimeters serve primarily to
measure jets and missing ET
Single hadron response (ie at test beams)
* indication of the level to be expected for jet
energy resolution
Make combined use of
* Tracker information
* Fine grained information from the ECAL and
HCAL detectors
* Measurement of jets can be significantly
improved
This holistic approach is often referred to as
‘Particle Flow Event Reconstruction’ Jets from a simulated event in CMS
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Introduction to Calorimetry 21.3.2012 37
Jets in CMS at the LHC, pp collisions at 7TeV
Red - ECAL, Blue - HCAL energy deposits
Yellow – Jet energy vectors
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Introduction to Calorimetry 21.3.2012 38
Jets and Particle Flow
Momenta of particles inside a jet
Example
Quark/gluon jet with a total pT of 500 GeV/c
Average pT carried by the stable constituent
particles of the jet ~ 10 GeV
Reduces to a ‘few’ GeV for the stable constituent
particles for jets with pT < 100 GeV
In a typical jet 65% of jet energy in charged hadrons
25% in photons (mainly from -> )
10% in neutral hadrons
For charged particles with ‘low’ momenta,
better to use momentum resolution of the tracker
than the energy resolution of the calorimeters
Only 10% of the jet energy (the neutral hadrons) left
to be measured in the ‘poor’ HCAL
Dramatic improvements for jet energy resolution
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Introduction to Calorimetry 21.3.2012 39
ETYPE/Ejet
0. 0.5 1.0
Charged
Hadrons
Energy fraction carried by particle type in a jet
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Introduction to Calorimetry 21.3.2012 40
Jets and Particle Flow
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Introduction to Calorimetry 21.3.2012 41
Jets and Particle Flow
Particle Flow versus Calorimetry alone
CMS - large central magnetic field of 4T
Very good charged particle track
momentum resolution
Good separation of charged particle
energy deposits from others in the
calorimeters
Good separation from other tracks
Large improvement in jet resolution
at low PT using the resolution of the
tracking system
Calorimetry only
Jet energy resolution as a function of PT
Simulated QCD-multijet events,
CMS barrel section: |η| < 1.5
Particle flow
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Introduction to Calorimetry 21.3.2012 42
Jets and Particle Flow
Missing ET normalised to the total transverse
energy for Di-jet events in CMS
with and without particle flow
Particle
Flow
Calorimetry
only
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Introduction to Calorimetry 21.3.2012 43
Jets and Particle Flow
CMS missing ET resolution
< 10 GeV on whole ΣET range
up to 350GeV.
Factor 2 improvement using
Particle Flow technique
Calorimetry
only
Particle
Flow
Missing ET resolution for Di-jet events
Di-jet
events
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Introduction to Calorimetry 21.3.2012 44
Detectors for Electromagnetic and Hadronic
Calorimetry
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Introduction to Calorimetry 21.3.2012 45
There are two general types of calorimeter design:
Sampling calorimeters
Layers of passive absorber (ie Pb or Cu) alternating with active
detector layers such as Si, scintillator or liquid argon
Only part of the energy is sampled
Used for both electromagnetic and hadron calorimetry
Calorimeter types
ATLAS ECAL & HCAL
LHCb ECAL
ALICE EMCAL
CMS HCAL
Homogeneous calorimeters
Single medium, both absorber and detector, eg:
Liquified Xe or Kr organic liquid scintillators
Dense crystal scintillators: PbWO4 CsI(Tl) BGO and many others
Lead loaded glass
Almost entirely for electromagnetic calorimetry
Si photodiode
or PMT
Babar ECAL CsI(Tl)
CMS ECAL (PbWO4 )
ALICE ECAL (PbWO4 )
PANDA ECAL (PbWO4 )
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Introduction to Calorimetry 21.3.2012 46
Lead tungstate crystals, CMS
Reasons for PbWO4
Homogeneous medium
Fast light emission ~80% of light in 25 ns
Short radiation length X0 = 0.89 cm
Small Molière radius RM = 2.10 cm
Emission peak 425 nm, matches to photo-detectors
Reasonable radiation resistance to very high doses
Emission spectrum (blue)
and transmission curve
425nm
350nm
70%
300nm 700nm
23cm
25.8Xo 22cm
24.7Xo
CMS Barrel crystal, tapered
~2.6x2.6 cm2 at rear
Avalanche PhotoDiode
readout
CMS Endcap crystal,
tapered, 3x3 cm2 at rear
Vacuum Photo Triode
readout
Downside
Only ~70 / MeV
(CsI, 5.104 / MeV)
Temp dependence -2% / oC
Extremely brittle
$$$/cc
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Introduction to Calorimetry 21.3.2012 47
Lead tungstate crystals, PbWO4
molten
seed
RF heating
Czochralski
method
A CMS PbWO4 crystal ‘boule’ emerging from its 1123oC melt
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Introduction to Calorimetry 21.3.2012 48
Lead tungstate crystals, CMS
Endcaps: 4 Dees (2 per Endcap)
14648 Crystals (1 type) – total mass 22.9 t
Barrel: 36 Supermodules (18 per half-barrel)
61200 Crystals (34 types) – total mass 67.4 t
Pb/Si Preshowers: 4 Dees (2/Endcap)
CMS at the LHC – scintillating PbWO4 crystals
Total of 75848
PbWO4 crystals
CMS Barrel, 61200 crystals
An endcap Dee, 3662 crystals awaiting
transport
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Introduction to Calorimetry 21.3.2012 49
Lead tungstate crystals, CMS
Barrel
Avalanche photodiodes(APD)
Two 5x5 mm2 APDs/crystal
Gain 50
QE ~75%
Temperature dependence -2.4%/OC
20
40m
Endcaps
Vacuum phototriodes(VPT)
More radiation resistant than Si
diodes
- UV glass window
- Active area ~ 280 mm2/crystal
- Gain 8 -10 (B=4T)
- Q.E. ~20% at 420nm
= 26.5 mm
MESH ANODE
CMS PbWO4 - photodetectors
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 50
Lead tungstate crystals, ALICE
ALICE at the LHC – scintillating PbWO4 crystals
Some of the 17,920 PbWO4 crystals for ALICE (PHOS)
Avalanche photo diode readout
D Cockerill, RAL, STFC, UK
STFC
RAL Lead tungstate crystals, CMS in-situ
Introduction to Calorimetry 21.3.2012 51
Energy resolution: the everyday challenges
Intercalibration of all the channels
Requires several steps before, during and after data taking
• test beam pre-calibration
• continuous monitoring during data taking
(short term changes)
• Intercalibration by physics reactions during running:
pi-zeros, etas, with specialized data-stream, phi symmetry
Currently intercalibrate to ~1.2% barrel, ~2-3% endcaps
Pi-zero - Data
Pi-zero - Monte Carlo
D Cockerill, RAL, STFC, UK
STFC
RAL Lead tungstate crystals, CMS in-situ
Introduction to Calorimetry 21.3.2012 52
CMS in-situ electromagnetic performance
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 53
Noble liquids for homogeneous calorimeters
Noble liquid calorimeters
I1
I2
q,ve -q, vI
Z=D
Z=0
E
Liquid Argon
5 mm/μs at 1 kV/cm,
5 mm gap 1 μs for all
electrons to reach the electrode.
Ion velocity 103 to 105 times
slower
doesn’t contribute to the
signal, for electronics with μs
integration times.
When charged particle traverses these materials, half
lost energy converted to ionisation, half to scintillation
Sometimes collected together – but difficult technically
Kr for most compact calorimeter: NA48, NA62 (from 2011)
Ar for low cost, high purity: ICARUS
Xe horribly expensive: Dark Matter searches
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 54
NA48 liquid Kr electromagnetic calorimeter
NA48 Liquid Krypton Ionisation chamber (T = 120K)
No metal absorbers: quasi homogeneous
Cu-Be ribbon electrode
2 cm x 2 cm cells
X0 = 4.7cm
125 cm length (27X0)
1 cm drift space
3 µs drift time
cathodes
anodes
2x2 cm2
cell
+/- 0.48 rad
e-
e-
e-
+3 kV
e-
e-
e-
+3 kV
photons from
os from Ko
decays
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 55
NA48 liquid Kr electromagnetic calorimeter
NA48 Liquid Krypton Ionisation chamber (T = 120K)
No metal absorbers: quasi homogeneous
En
erg
y re
so
lution
Energy (GeV) Energy (GeV)
Po
sitio
n r
eso
lutio
n (
mm
)
Energy (GeV)
Po
sitio
n r
eso
lutio
n (
mm
)
Y
X
Position resolution Energy resolution, blue after unfolding
spectrometer resolution
a = 3.2% b = 9%/E c = 0.42%
D Cockerill, RAL, STFC, UK
STFC
RAL ATLAS sampling electromagnetic calorimeter
Introduction to Calorimetry 21.3.2012 56
6.4 m
Barrel em 114 t
Inner radius 1.4 m
Depth 53 cm, 22-30 Xo
D Cockerill, RAL, STFC, UK
STFC
RAL ATLAS sampling electromagnetic calorimeter
Introduction to Calorimetry 21.3.2012 57
Absorbers immersed in liquid argon (90K)
Multilayer Cu-polyimide readout boards
Electric field to collect ionisation
1 GeV energy deposit 5.106 e-
Accordion geometry minimises dead zones
Liquid argon intrinsically rad hard
Readout board allows fine segmentation
(azimuth, rapidity, longitudinal)
1-2mm thick stainless
steel folded plates
2.1 mm drift gap
450 ns drift time
D Cockerill, RAL, STFC, UK
STFC
RAL ATLAS sampling electromagnetic calorimeter
Introduction to Calorimetry 21.3.2012 58
Photon Pi-zero
Readout grouping into trigger
towers
25 Xo total
4 Xo fine grain, pizero rejection
16 Xo shower core
2 Xo to evaluate late starters
170,000 channels
D Cockerill, RAL, STFC, UK
STFC
RAL ATLAS sampling electromagnetic calorimeter
Introduction to Calorimetry 21.3.2012 59
Ebeam (GeV)
E/E
Energy resolution at test
beam
Mean energy response at
three eta locations
D Cockerill, RAL, STFC, UK
STFC
RAL ATLAS sampling electromagnetic calorimeter
Introduction to Calorimetry 21.3.2012 60
ATLAS results for J/Psi and Z
D Cockerill, RAL, STFC, UK
STFC
RAL LHCb calorimeters
Introduction to Calorimetry 21.3.2012 61
HCAL ECAL Presampling
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 62
LHCb (and ALICE) sampling electromagnetic calorimeters at the LHC
LHCb module
67 scintillator tiles, each 4 mm thick, interleavedwith 66 lead plates, each 2 mm thick
Readout through wavelength shifting fibres running through plates to phototubes
Back plate
Compressionplate
WLS fibres
Pb/scintillatorstack
Front plate
Mirrored end of fibres
Black foil for blocking light
Strap
Belleville
washers
Tower “A”
Tower “B”
Alice fibre
collection to APDs
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 63
LHCb sampling electromagnetic calorimeter
Wall of 3312
modules
D Cockerill, RAL, STFC, UK
STFC
RAL LHCb sampling electromagnetic calorimeter
Introduction to Calorimetry 21.3.2012 64
LHCb test beam results LHCb in-situ results, pi-zero
and eta signals
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 65
CMS Hadron Sampling Calorimeter
Workers in Murmansk
sitting on brass casings of
decommissioned shells of
the Russian Northern Fleet
Explosives previously
removed!
Casings melted in St
Petersburg and turned into
raw brass plates
Machined in Minsk and
mounted to become
absorber plates for the CMS
Endcap Hadron Calorimeter
CMS Hadron calorimeter at the LHC Brass absorber preparation
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 66
The CMS HCAL being inserted into the solenoid
Light produced in the scintillators is transported through optical fibres to
Hybrid Photo Diode (HPD) detectors
CMS Hadron Sampling Calorimeter
Scintillator tile inspection
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 67
CMS HCAL – fibre readout
Wavelength shifter and fibre optic readout for the CMS
scintillator tiles
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 68
CMS Hadron and EM calorimetry
CMS
Barrel
HCAL
CMS
Endcap
HCAL
CMS
Endcap
ECAL
D Cockerill, RAL, STFC, UK
STFC
RAL Liquid scintillator detectors
Introduction to Calorimetry 21.3.2012 69
Borexino
* Detect solar neutrinos (7Be, 0.86 MeV)
* Acceptance ~ 200 keV to a few MeV
* 300 t of ultra pure organic liquid
scintillator
* Minimise background from
radioactive contamination
* 500 photo-electrons/MeV
* 5% resolution at 1 MeV
Kamland: 18 m across !!
* Detect anti-neutrinos from power
reactors above ~ 0.7 MeV
* 1000 t of ultra pure organic
liquid scintillator
* Minimise background from
radioactive contamination
* 300 photo-electrons/MeV
* 7.5% resolution at 1 MeV
D Cockerill, RAL, STFC, UK
STFC
RAL Liquid scintillator detectors
Introduction to Calorimetry 21.3.2012 70
Inside Borexino,
before filling !!
PM tubes with
Winston cone light
collectors
D Cockerill, RAL, STFC, UK
STFC
RAL Future directions in Calorimetry
The International Linear Collider (ILC)
Exploit Particle Flow techniques Need very high transverse segmentation
ECAL ~1x1 cm2 SiW project – CALICE HCAL ~3x3 cm2 Steel/scintillator
High longitudinal sampling, 30 layers ECAL and 40 layers HCAL
CALICE prototype, 1.4/2.8/4.2mm thick W plates (30X0) interleaved with Silicon
wafer, read out with 1x1cm2 pads. Resolution a ~17%, c ~ 1.1%
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
CMS, pp -> 2 photons + X, at 7 TeV in search for H -> , ECAL red, HCAL blue
No tracks
towards large
em deposits
=> photons
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
Introduction to Calorimetry 21.3.2012 73
CMS r-phi (end on) view pp -> 2 electrons + X, 7 TeV
ECAL red, HCAL blue
Z’ -> 2e search
Effective mass
Mee = 1309 GeV
Track towards each
large em deposit
2 electrons
Rather quiet elsewhere
840 GeV
748 GeV
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
Introduction to Calorimetry 21.3.2012 74
Track towards each
large em deposit
2 electrons
Rather quiet elsewhere
CMS side view
pp -> 2 electrons + X
7 TeV
ECAL red, HCAL blue
Z’ -> 2e search
Effective mass
Mee = 1309 GeV
840 GeV
748 GeV
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
Introduction to Calorimetry 21.3.2012 75
CMS
Dijet event from pp collision at 7 TeV
Effective mass 4696.74 GeV
Hard scatter involving over 65% of
the available collision energy
ECAL red
HCAL blue
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
Introduction to Calorimetry 21.3.2012 76
CMS Event with 5 jets from pp collision at 7 TeV
ECAL red
HCAL blue
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
Heavy ion collision in CMS, Pb-Pb, Nov 2010, ECAL red, HCAL blue
D Cockerill, RAL, STFC, UK
STFC
RAL Calorimeters at work
Heavy ion collision in CMS, Pb-Pb, Nov 2010, ECAL red, HCAL blue
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 79
Summary
Calorimetry is one of the most important detector techniques for particle physics
Calorimeters playing a crucial role for physics at the LHC
eg H → γγ, Z’ → ee, SUSY (missing ET)
Wide variety of mature and new technologies are available
Calorimeter design is dictated by physics goals and experimental constraints
Compromises often necessary, ie in choosing between high resolution
e.m. calorimetry or high resolution hadron calorimetry
References:
Electromagnetic Calorimetry, Brown and Cockerill, NIM-A 666 (2012) 47–79
Calorimetry for particle physics, Fabian and Gianotti, Rev Mod Phys, 75, 1243 (2003)
Calorimetry, Energy measurement in particle physics, Wigmans, OUP (2000)
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 80
Backups
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 81
Homogeneous e.m. calorimeters
Electron energy resolution
as a function of energy
Electrons centrally (4mmx4mm)
incident on crystal
Resolution 0.4% at 120 GeV
Energy resolution at 120 GeV
Electrons incident over full crystal face
Energy sum over 5x5 array wrt hit crystal.
Universal position ‘correction function’ for
the reconstructed energy applied
Resolution 0.44%
Stochastic term
Constant term
Noise term
Barrel Barrel
PbWO4 - CMS ECAL energy resolution
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 82
Homogeneous calorimeters
Three main types: Scintillating crystals Glass blocks (Cerenkov radiation) Noble liquids
Homogeneous calorimeters
Barbar
@PEPII
10ms
inter’n rate
good light
yield, good S/N
KTeV at
Tevatron,
High rate,
Good
resolution
L3@LEP,
25s bunch
crossing,
Low rad’n
dose
CMS at LHC
25ns bunch
crossing,
high radiation
dose
ALICE
PANDA
Crystals
Lead glass, SF-6
OPAL at LEP
Xo = 1.69cm,
= 5.2 g/cm3
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 83
Variation in the lattice
(e.g. defects and impurities)
local electronic energy levels in the energy gap
The centres are of three main types:
• Luminescence centres in which the transition to the ground state
is accompaigned by photon emission
• Quenching centres in which radiationless thermal dissipation of
excitation energy may occur
• Traps which have metastable levels from which the electrons may
subsequently return to the conduction band by acquiring thermal
energy from the lattice vibrations or fall to the valence band by
a radiationless transition
If these levels are unoccupied electrons moving in the conduction
band may enter these centres
Scintillating crystals
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 84
200 300 400 500 600 700
inte
ns
ity (
a.u
.)
wavelength (nm)
Stokes shift PWO relaxation
-50
0
50
100
150
200
250
-400 -300 -200 -100 0 100 200 300 400
En
erg
y
Configurational
coordinates
DEa
excited
stateground
state
hnex hn
em
Stokes shift
Dl = lem
- lex
Q0
gQ
0
eA
B
C
D
excitation
radiative emission
PbWO4: lexcit=300nm ; lemiss=500nm
Scintillating crystals
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 85
Conduction band
valence band
band
gap
Edep e-h
Es= b Eg b>1
Neh = Edep / bEg
Efficiency of transfer to luminescent centres
radiative efficiency of luminescent centres
N = SQNeh
= N / Edep= SQNeh / Edep = SQ/ bEg
• S, Q 1 , bEg as small as possible
• medium transparent to lemiss
Eg
Scintillating crystals
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 86
CMS Barrel and Endcap Homogeneous ECAL
A CMS Supermodule
with 1700 tungstate crystals Installation of the last SM into
the first half of the barrel
A CMS endcap ‘supercrystal’
25 crystals/VPTs
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 87
Electromagnetic shower
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 88
D Cockerill, RAL, STFC, UK
STFC
RAL
Introduction to Calorimetry 21.3.2012 89
Lead tungstate crystals, CMS in-situ
Measurement of the Z peak using Z->ee decays
with the PbWO4 crystals of the CMS ECAL at the LHC
CMS ECAL
Instrumental
resolution:
1.0 GeV
in ECAL Barrel
for the Z peak
(91 GeV) Note the hard
work needed for
various detector
corrections