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Calorimetry and Showers
Learning Objectives
• Understand the basic operation of a calorimeter (Measure the energy of a particle, and in the process, destroy it)
• Understand the difference between an electromagnetic shower and a hadronic shower
• Understand the similarity between measuring a particle’s energy with a calorimeter and with a ground-based array of detectors (for cosmic ray air showers)
Outline
• Reminder on extended cosmic-ray air showers
• Calorimeters in High Energy Physics• Generic layout
• Electromagnetic (EM) showers• Bremsstrahlung (“braking radiation”)• Pair production• Depth development of EM showers
• Hadronic showers• Comparison to EM showers
• Calorimeter read-out schemes
• Energy resolution
• Calorimeter example• Fermilab APEX experiment
Calorimetery and Showers
Terminology
Calorimetery and Showers
• High-energy electrons and photons initiate “electromagnetic” showers in matter (solid, liquid, gas)• These particles do not feel the “strong” force, and hence do not initiate “hadronic” showers.
• Hadrons are particles which consist of quarks and gluons• Hadrons feel the “strong” force and initiate “hadronic” showers in matter
• Two categories of hadrons• Baryons
• Consist of 3 quarks or 3 anti-quarks plus gluons• Examples: proton, neutron, antiproton
• Mesons• Consist of a quark and an anti-quark plus gluons• Examples: pion (“pi-meson”), kaon (“k-meson”)
• Hadronic showers usually contain electromagnetic showers
FermilabFermi National Accelerator Laboratory
Batavia, Illinois
Main Injector(new)
Tevatron
DØCDF
Chicago
p source
Booster
The “D0” DetectorInternational collaboration
• Inner layers: Tracking chambersAll particles pass through
• Next layers: CalorimetersAll particles (except muons, neutrinos) destroyed, and energy measured
• Outer layers: Muon tracking chambersOnly muons and neutrinos penetrate through
Calorimeters in High-EnergyPhysics Experiments
Fermilab, Batavia, Illinois
CERN, Geneva, Switzerland
Protons
Anti-protonsNote layeredstructure ofcalorimeters
The “D0” Detector
The CMS Detector
Calorimetry and Showers
Radiation length
Number of particles 1 2 4 8 …….
The longitudinal (depth) development of anelectromagnetic shower
e-
e-
e-
e+
Bremsstrahlung
Pair productionPhoton or “gamma” ray
Calorimetry and Showers
Radiation Lengths in Different Materials
Radiation length, X0
e-
e-
e-
e+
Bremsstrahlung
Pair productionPhoton or “gamma” ray
Material Radiation length, X0
Uranium (U) 0.32 cmLead (Pb) 0.56 cmWater (H20) 36.1 cm (14 inches)Air at S.T.P. 304.2 m (998 feet)
These values are listed in the small “Particle PhysicsBooklet” given to each school.
Calorimetry and Showers
Depth Development of Electromagnetic Showers
• Higher energy particles push “shower maximum” deeper into material• Depth of shower maximum ln (Energy elec or )
Increasing depth in radiator material measuredin radiation lengths
High energyelectrons
Low energyelectronsN
um
ber
of
elec
tron
s in
sh
ower
Calorimetry and Showers
Measured energy distributions for 4 different incident electron energies
Average measuredenergy
Width ofdistribution
is“Energy
Resolution”
• Above distributions come from measuring many, many particles incident on the calorimeter
• Note the spread in measured energies due to statistical fluctuations in shower development
Energy measured by calorimeter
Precisely measured beam energies (GeV)
• Particle masses (in energy units):• Electron 0.511 MeV Fundamental particle• Muon 106 MeV Fundamental particle• Pion 140 MeV Two quarks• Proton 938 MeV Three quarks
Hadronic showers
Calorimetry and Showers
• In a hadronic shower, most of the scondaries are pions
• Pions come in three charge states:
They go on to either• Create another hadronic shower• Decay to a muon and a neutrino
They decay immediately to twophotons (), which then createelectromagnetic showers
lifetime = 8.4 10-17 seconds• lifetime = 2.6 10-8 seconds• Muon lifetime = 2.2 10-6 seconds
Calorimetry and Showers
Interaction Lengths in Different Materials
Material Interaction length, I
Copper (Cu) 15.1 cmIron (Fe) 16.8 cmWater (H20) 84.9 cm (33 inches)Air at S.T.P. 758 m (2486 feet)
These values are listed in the small “Particle PhysicsBooklet” given to each school.
Calorimetry and Showers
Interaction length
Depth development of a hadronic shower
Hadronic showers are deeper and wider thanelectromagnetic showers
Calorimetry and Showers
Examples of Calorimeter Read-out Schemes
Lead-scintillatorsandwich
Sandwich of lead andmulti-wire proportionalchambers
Lead-liquid argonsandwich
Lead-scintillatorsandwich with wavelength-shiftingbars on side of module