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 eV Extensive Air Shower

Fermilab Fermi National Accelerator Laboratory Batavia, Illinois Main Injector (new) Tevatron DØCDF Chicago   p source Booster

The “D0” Detector International collaboration Inner layers: Tracking chambers All particles pass through Next layers: Calorimeters All particles (except muons, neutrinos) destroyed, and energy measured Outer layers: Muon tracking chambers Only muons and neutrinos penetrate through

Calorimeters in High-Energy Physics Experiments Fermilab, Batavia, Illinois CERN, Geneva, Switzerland Protons Anti-protons Note layered structure of calorimeters The “D0” Detector The CMS Detector

Calorimetry and Showers Radiation length Number of particles ……. The longitudinal (depth) development of an electromagnetic shower e-e- e-e- e-e- e+e+  Bremsstrahlung Pair production Photon or “gamma” ray

Calorimetry and Showers Radiation Lengths in Different Materials Radiation length, X 0 e-e- e-e- e-e- e+e+  Bremsstrahlung Pair production Photon or “gamma” ray Material Radiation length, X 0 Uranium (U) 0.32 cm Lead (Pb) 0.56 cm Water (H 2 0) 36.1 cm (14 inches) Air at S.T.P m (998 feet) These values are listed in the small “Particle Physics Booklet” 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 measured in radiation lengths High energy electrons Low energy electrons Number of electrons in shower

Calorimetry and Showers Measured energy distributions for 4 different incident electron energies Average measured energy Width of distribution 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 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 two photons (  ), which then create electromagnetic showers     lifetime = 8.4  seconds     lifetime = 2.6  seconds Muon lifetime = 2.2  seconds

Calorimetry and Showers Interaction Lengths in Different Materials Material Interaction length, I Copper (Cu) 15.1 cm Iron (Fe) 16.8 cm Water (H 2 0) 84.9 cm (33 inches) Air at S.T.P. 758 m (2486 feet) These values are listed in the small “Particle Physics Booklet” given to each school.

Calorimetry and Showers

Interaction length Depth development of a hadronic shower Hadronic showers are deeper and wider than electromagnetic showers

Calorimetry and Showers Examples of Calorimeter Read-out Schemes Lead-scintillator sandwich Sandwich of lead and multi-wire proportional chambers Lead-liquid argon sandwich Lead-scintillator sandwich with wavelength-shifting bars on side of module

Calorimetry and Showers