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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

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detectors measurements how we do physics without seeing

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

Lectures from CERN, Erbacher, Conway, …

the standard model
The Standard Model

A Higgs field interacts

as well, giving particles

their masses.


The SM states that:

The world is made

up of quarks and

leptons that interact

by exchanging


35 times heavier

than b quark

Lepton Masses:Me<M<M ; M~0.*

Quark Masses:Mu ~ Md < Ms < Mc< Mb << Mt

particle reactions
Particle Reactions


  • 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
rare collision events
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.


Cartoon by Claus Grupen, University of Seigen

global detector systems
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)
ideal detectors
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
individual detector types
Individual Detector Types

Modern detectors consist of many different pieces of

equipment to measure different aspects of an event.

Measuring a particle’s properties:

  • Position
  • Momentum
  • Energy
  • Charge
  • Type
particle decay signatures
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.


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.

modern collider detectors
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!
cdf top pair event

b quark jets

high pT


missing ET

b-quark lifetime:

c ~ 450m

 b quarks travel

~3 mm before decay

q jet 1

q jet 2

CDF Top PairEvent
particle detection methods
Particle Detection Methods

Signature Detector Type Particle

Jet of hadrons Calorimeter u, c, tWb,

d, s, b, g

‘Missing’ energy Calorimeter e, , 


shower, Xo EM Calorimeter e,, We

Purely ionization

interactions, dE/dx Muon Absorber , 

Decays,c ≥ 100m Si tracking c, b, 

particle identification methods

PID = Particle ID

(TOF, C, dE/dx)


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

quiz decays of a z boson
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!

geometry of cdf
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
cdf run 2 detector

Endwall Calorimeter

Central Outer Tracker

Silicon Vertex


New Endplug Calorimeter

CDF Run 2 Detector
call em spectrometers
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:
magnets for 4 detectors
Magnets for 4 Detectors



+ 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
charge and momentum
Charge and Momentum

Two ATLAS toroid coils

Superconducting CMS Solenoid Design

cms spectrometer details
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
  • 4π muon coverage
  • 25-nsec bunch crossing time
  • 10 Mrad radiation dose to inner detectors
  • ...
cms all silicon tracker
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

possible future at the ilc sid
Possible Future at the ILC: SiD

All silicon sensors:

pixel/strip tracking

“imaging” calorimeter

using tungsten with Si wafers

fixed target spectrometers
Fixed Target Spectrometers

Coming next time…