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

Development of Giant Air Shower in Earth’s Atmosphere

A 1019 eV Extensive Air Shower

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

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

Calorimetry and Showers