HW

1
Read Das and Ferbel Chap. 8.

• HW 4 solutions are posted.
• HW 5 assignment has been posted. It will be due
  March 26 (Wednesday after spring break).
• The website for the Data Analysis Workshop will
  be ready for action by tomorrow morning.
• Tim Klein (klein_at_physics.umn.edu - CLEO senior
  graduate student) and I will provide consulting
  services by email. Tim will have office hours
  during the DAW in Rm. 253 (or 137) 400 - 500 pm
  on M, T, W, and Th.
• There will be four assignments, which you will
  hand in by email to klein_at_physics.umn.edu.
• The first weeks activity is a warm-up exercise
  to allow you to get familiar with the
  environment, documentation and software.

2
Semi-Quantitative EM Shower Model

• Follow shower development until the particle
  energies reach Ec? 600 MeV/Z (7 MeV for Pb),
  where ionization equals Brems.
• Electron with E Ec travels 1 radiation length
  and gives up half of its energy to a Brems ?.
• Photon with E Ec travels 1 radiation length and
  creates ee?, splitting E equally.
• Electron with E remaining energy by ionization.

Electrons all Brems above Ec and all ionization
below.

• After t radiation lengths, 2t particles, equal
  proportions of e, e?, ?.
• Average energy E(t) E0/2t.
• Shower stops at E(t) Ec, shower max

3
Semi-Quantitative EM Shower Model

• Follow shower development until the particle
  energies reach Ec? 600 MeV/Z (7 MeV for Pb),
  where ionization equals Brems.
• Electron with E Ec ionizes for 1 radiation
  length and gives up half of its energy to a Brems
  ?.
• Photon with E Ec travels 1 radiation length and
  creates ee?, splitting E equally.
• Electron with E remaining energy by ionization.

Electrons all Brems above Ec and all ionization
below.

• After t radiation lengths, 2t particles, equally
  e, e?, ?, average energy E(t) E0/2t.
• Shower stops at E(t) Ec, shower max

Does quite a good job, except that it does not
predict the energy resolution, which results from
fluctuations and must be simulated.
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5
Sampling Calorimeters
Metal-scintillator sandwich - Plastic
scintillator, Pb/steel plates - Cheap, poor E
resolution, fast, easy to build/operate
Metal-liquid-argon sandwich - 1-mm Pb
plates, 2-mm gaps - LAr ionization chamber
- Good E resolution, slow,
6
Hadronic Interactions ? Hadron Calorimeters

• Most particles in HE processes are hadrons
• Charged ones lose energy by ionization
  (Bethe-Bloch) both charged and neutral
  experience elastic and inelastic strong
  interactions when they get close enough to a
  nucleus.
• At low energy elastic dominates until something
  else can happen. Behavior is complicated,
  depends on charge, structure of specific hadron
  different cross sections for different kinds of
  hadrons, resonant structure (excitations), etc.
• For ?p, elastic dominates to 700 MeV/c, when
  threshold is reached for producing additional
  particles. For ??p, elastic dominance ends at
  smaller energy because of the possibility of
  quasi-elastic (charge-exchange) scatters ?? p ?
  ?0 n.
• At higher energy things get simpler
• Above 5 GeV total cross section falls slowly
  with energy. The minimum of 20-40 mb (??R2)
  occurs at 70-100 GeV.
• Above 100 GeV, total cross section rises slowly
  (log) with energy.

7
?p
vs.
Kp
8
?p

• Some general comments
• Cross section is big!
• Most collIsions have small q2. Hard scatters
  rare, interesting!
• Mean multiplicity goes from 3 at 5 GeV to 12
  at 500 GeV (log).
• First hadronic interaction triggers hadronic
  shower, similar but slower developing than EM
  shower.
• Hadron calorimeters (sampling!) and muon ID need
  thick absorbers.

vs.

• Length scale for hadronic interactions

??p
9

• We havent covered everything, but we have
  introduced most of the building blocks of modern
  EPP/NP detectors.
• Detector design requires selecting subsystems
  that accomplish specific goals of the experiment
  with minimum negative impact while not
  compromising other goals and not requiring
  infinite resources.
• Look at some generic and specific detectors

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