Detectors

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Detectors Measurements How we do physics
without seeing
Overview of Detectors and Fundamental
Measurements From Quarks to Lifetimes

• Prof. Robin D. Erbacher
• University of California, Davis

References R. Fernow, Introduction to
Experimental Particle Physics, Ch. 14, 15
D. Green, The Physics of Particle
Detectors, Ch. 13
http//pdg.lbl.gov/2004/reviews/pardetrpp.pdf
Lectures from CERN, Erbacher,
Conway,
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The Standard Model
The SM states that The world is made up of
quarks and leptons that interact by exchanging
bosons.
35 times heavier than b quark
Lepton Masses MeltM?ltM? M?0.
Quark Masses Mu Md lt Ms lt Mclt Mb ltlt Mt
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Particle Reactions
Time

• Idealistic View
• Elementary Particle Reaction
• Usually cannot see the reaction itself
• To reconstruct the process and the particle
  properties, need maximum information about
  end-products

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Complicated Collisions
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Rare Collision Events
Rare Events, such as Higgs production, are
difficult to find! Need good detectors,
triggers, readout to reconstruct the mess into a
piece of physics.
Time
Cartoon by Claus Grupen, University of Seigen
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We dont use bubble chambers anymore!
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Global Detector Systems

• Overall Design Depends on
• Number of particles
• Event topology
• Momentum/energy
• Particle identity

?
No single detector does it all ? Create
detector systems
Collider Geometry
Fixed Target Geometry

• full solid angle d? coverage
• Very restricted access

• Limited solid angle (d?? coverage (forward)
• Easy access (cables, maintenance)

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Ideal Detectors
End products

• An ideal particle detector would provide
• Coverage of full solid angle, no cracks, fine
  segmentation (why?)
• Measurement of momentum and energy
• Detection, tracking, and identification of all
  particles (mass, charge)
• Fast response no dead time (what is dead time?)
• However, practical limitations Technology,
  Space, Budget

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Individual Detector Types
Modern detectors consist of many different pieces
of equipment to measure different aspects of an
event.

• Measuring a particles properties
• Position
• Momentum
• Energy
• Charge
• Type

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Particle Decay Signatures
Particles are detected via their interaction with
matter. Many types of interactions are involved,
mainly electromagnetic. In the end, always rely
on ionization and excitation of matter.
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Jets
Jet (jet) n. a collimated spray of high energy
hadrons
Quarks fragment into many particles to form a
jet, depositing energy in both calorimeters. Jet
shapes narrower at high ET.
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Modern Collider Detectors

• the basic idea is to measure charged particles,
  photons, jets, missing energy accurately
• want as little material in the middle to avoid
  multiple scattering
• cylinder wins out over sphere for obvious reasons!

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CDF Top Pair Event
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CDF Top Pair Event
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Particle Detection Methods
Signature Detector Type
Particle
Jet of hadrons Calorimeter
u, c, t?Wb,
d, s, b,
g Missing energy Calorimeter
?e, ??, ?? Electromagnetic shower,
Xo EM Calorimeter e, ?,
W?e? Purely ionization interactions, dE/dx
Muon Absorber ?, ????? Decays,c?
100?m Si tracking c, b, ?
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Aleph at LEP (CERN)
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Particle Identification Methods
Constituent Si Vertex Track PID
Ecal Hcal Muon
electron primary ? ?
? Photon
????????????primary ?
u, d, gluon primary
? ? ?
Neutrino??
s
primary ? ?
? ? c, b, ?
secondary ? ? ? ?
? primary
? MIP MIP ?
MIP Minimum Ionizing Particle
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Quiz Decays of a Z boson
Z bosons have a very short lifetime, decaying in
10-27 s, so that only decay particles are seen
in the detector. By looking at these detector
signatures, identify
the daughters of the Z boson.
But some daughters can also decay
More Fun with Z Bosons, Click Here!
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CDF Schematic
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Geometry of CDF

• calorimeter is arranged in projective towers
  pointing at the interaction region
• most of the depth is for the hadronic part of the
  calorimeter

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CDF Run 2 Detector
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QCD Di-Jet Event, Calorimeter Unfolded
Central/Plug Di-Jet
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Unfolded Top/anti-Top Candidate
Run 1 Event
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Unfolded Top/anti-Top Candidate
Run 2 Event
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Call em Spectrometers

• a spectrometer is a tool to measure the
  momentum spectrum of a particle in general
• one needs a magnet, and tracking detectors to
  determine momentum
• helical trajectory deviates due to radiation E
  losses, spatial inhomogeneities in B field,
  multiple scattering, ionization
• Approximately

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Magnets for 4? Detectors
Solenoid
Toroid
Large homogeneous field inside - Weak opposite
field in return yoke - Size limited by cost -
Relatively large material budget
Field always perpendicular to p Rel. large
fields over large volume Rel. low material
budget - Non-uniform field - Complex structural
design

• Examples
• Delphi SC, 1.2 T, 5.2 m, L 7.4 m
• L3 NC, 0.5 T, 11.9 m, L 11.9 m
• CMS SC, 4 T, 5.9 m, L 12.5 m

• Example
• ATLAS Barrel air toroid, SC, 1 T, 9.4 m, L 24.3
  m

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Charge and Momentum
Two ATLAS toroid coils
Superconducting CMS Solenoid Design
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Charge and Momentum
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CMS at CERN
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CMS Muon Chambers
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CMS Spectrometer Details

• 12,500 tons (steel, mostly, for the magnetic
  return and hadron calorimeter)
• 4 T solenoid magnet
• 10,000,000 channels of silicon tracking (no gas)
• lead-tungstate electromagnetic calorimeter
• 4p muon coverage
• 25-nsec bunch crossing time
• 10 Mrad radiation dose to inner detectors
• ...

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CMS All Silicon Tracker
All silicon pixels and strips!
210 m2 silicon sensors 6,136 thin
detectors (1 sensor) 9,096 thick detectors
(2 sensors) 9,648,128 electronics channels
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Possible Future at the ILC SiD
All silicon sensors pixel/strip
tracking imaging calorimeter using tungsten
with Si wafers
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Fixed Target Spectrometers
Coming next time