Calorimeters in Particle Physics

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Calorimeters in Particle Physics

• What do they do?
• Measure the ENERGY of particles
• Electromagnetic Energy
• Electrons, positrons, photons
• Hadronic Energy
• Charged pions, protons
• Particle ID
• Distinguish between different particles
• Sometimes in combination with tracking etc
• Why?
• Measure particles coming out of Interaction
• Reconstruct what happened
• Remember the first lab on Monday particle
  search

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Calorimeters versus Tracking

• Tracking makes precision measurement of position
  of CHARGED particle trajectory
• Reconstruct displaced vertex
• Particle ID like in b-quark tagging
• Measure momentum charge in combination with
  magnetic field
• Radius of curvature
• Calorimeters measure amount of electromagnetic
  and hadronic ENERGY
• Measure of E,P are complimentary
• e.g. No track .AND. EM energy ? photon

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The life of a particle in a detector
vertex
momentum
ID
em energy
h energy
Muon ID,p
e
g
p
m
n
precision
normal
Particle ID
electromagnetic
hadronic
Muon Tracking
Tracking
Calorimeters
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Calorimeters are after tracking
Tracking measures particles as the traverse the
medium (e.g. gas, thin silicon) without
disturbing the particle. Calorimeters
destroy (i.e.stop) the particle to measure
their energy - some exceptions are neutrinos
and muons.
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Real top-quark event
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Electromagnetic Calorimeter
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Electromagnetic Shower
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Longitudinal Profile
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How to build a good em calorimeter

• Large number X0 with small chance of hadron
  interacting
• Want to stop em particles NOT hadrons
• small radiation length (X0)
• Large interaction length (lh)
• Want to get good sampling of particles in shower
  to get good statistical sampling of energy.
• Stacked plates of High z absorber (e.g. Pb, U,
  Fe) and detectors (e.g. scintillator, Liquid
  Argon)
• Certain crystals (e.g. Pb, CsI)

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Examples
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Energy Resolution
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Energy Resolution
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Reconstruct particles
p0 ? g g
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Reconstructed Z Boson Mass
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Reconstruct the event