Calorimetry at ATLAS and CMS Mauricio Romo

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Calorimetry at ATLAS and CMSMauricio Romo
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Outline

• Review of EM Calorimetry
• Review of Hadronic Calorimetry
• ATLAS ECAL
• CMS ECAL
• ATLAS HCAL
• CMS HCAL
• Comparison of Resolutions

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Electromagnetic calorimetry

• Calorimeters are mean to determine particles
  energy and directions
• Charged particles involved in the process e, e-
  and ?
• At E lt 100 Gev only electrons, positrons and
  photons are relativistic enough to emit
  significant radiation

Energy loss by electrons - Ionization
- Radiation
Bremsstrahlung
- Multiple Coulomb Scattering Energy
loss by photons - Photoelectric Effect
- Compton
Scattering
- Pair production
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Energy loss by radiation Bremsstrahlung
For high Z
Radiation Lenght
Critical energy
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Pair production
The photon must have E gt 1022 MeV to produce a
pair
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EM showers
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Moliere radius
Transverse spread of the shower
90 (95) of the energy of the shower is
contained in 1 (2) Moliere radius
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Types of calorimeters
Sampling Calorimeter
Homogeneus Calorimeter
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Energy resolution
a stochastic term, due to fluctuations in the
sampling b electronic noise c detector
disuniformities or instabilities
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Hadronic calorimetry
- Particles that interacts strongly (Baryons,
Mesons)
- Nuclear free path in gr/cm2
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Hadronic showers

• Pions are the lightest hadrons
• We expect that emitted particles are 2/3 charged
  and 1/3 neutral
• p0 quickly decays into two photons, developing an
  EM component

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Energy resolution
The constant term also takes into account the e/h
ratio or the difference on the response of the
calorimeter to hadronic showers and EM showers
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ATLAS CMS experiments
ECAL 25 X0 HCAL 6 ?I HO 4 ?I
ECAL 22.3 X0 HCAL 8 ?I
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ATLAS EM calorimeter
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ATLAS EM calorimeter
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ATLAS EM calorimeter
Lead liquid-argon sampling calorimeter
Barrel ? lt 1.4 End Caps 1.4 lt ? lt
3.2 Depth Pb/LAr 24-26 X0
lead ? 11.4 g/cm3 X0 5.5 mm LAr X0 14.2
cm RM 10.1 cm
RM 2 cm

• Lead plates interspersed with liquid argon in
  gaps
• Accordion geometry
• Argon gaps decreases linearly with ?, then
• output signal grows with ?
• -Shower develops mainly in the lead
• Electrons lose energy by ionisation and release
  charge in liquid argon that is collected on
  electrodes charge collected ? energy

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ATLAS EM calorimeter
Lead liquid-argon sampling calorimeter

• LAr features
• High electron movility
• Noble gas
• Liquid (easy to adopt the geometry)

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CMS EM calorimeter
PbWO4 crystal calorimeter

• All energy of particles released in active medium
• Electrons in shower produce light that is
  converted to electrical signals by Avalanche
  Photo Diodes (APDs) and Vacuum Photo Triodes
  (VPTs)

Crystal properties ? 8.28 g/cm3 X0 0.89 cm ?I
22.4 cm RM 2.19 cm
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Resolution comparison for ECAL
CMS a 2.7 b 0.55 c 0.2 GeV
ATLAS a 10 b 0.5 c 0.2 GeV
As we can see CMS resolution for the EM
calorimeter is slightly better than ATLAS
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Photon Energy resolution
ATLAS CMS
For mH120 GeV , E?60 GeV
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ATLAS Hadronic calorimeter
- Central Hadronic ? lt 1.7 Fe/Scintillator Tile
structure - End Cap Hadronic 1.7 lt ? lt 3.2
Cu/LAr -Forward calorimeter 3 lt ? lt 4.9 EM
Cu/LAr HAD W/LAr Depth 9.7-13 ?I
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CMS Hadronic calorimeter

• Barrel HCal ? lt 1.74, Brass/Scintillator
• -End Cap HCAL 1.3lt?lt3.0, Brass/Scintillator
• -Forward calorimeter 3 lt ? lt 5
• Fe/Quartz Fibre

EM barrel and EndCap
Very Forward Calorimeter
Hcal barrel and EndCap
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Resolution comparison for HCAL
CMS a 75 c 8
ATLAS a 45 c 1.3
The overall resolution for pions is far better
for ATLAS. I seems like Cu/LAr is better than the
Brass/Scintillator system used at CMS.
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Jet resolution comparison
t-jets
ATLAS CMS
For Ejet60 Gev
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MET resolution comparison
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Overall resolution comparison
EM LAr TileCal resolution (obtained at 1998
Combined TestBeam, ?0.35)
As result the overall reesolution for ATLAS is
better than CMS
Single p resolution (HADEM obtained at combined
test beam 1996)