Detectors & Measurements II:
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, …
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!
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:
dp q
 vB
dt c
• helical trajectory deviates due to radiation E
losses, spatial inhomogeneities in B field,
multiple
 scattering, ionization
• Approximately:
p  0.2998B T - m
 = radius of curvature
Magnets for 4 Detectors
Solenoid
+ Large homogeneous field inside
- Weak opposite field in return yoke
- Size limited by cost
- Relatively large material budget
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
Toroid
+ Field always perpendicular to p
+ Rel. large fields over large volume
+ Rel. low material budget
- Non-uniform field
- Complex structural design
Example:
•ATLAS: Barrel air toroid, SC, ~1 T, 9.4
m, L 24.3 m
LHC Coils Different
Two ATLAS toroid coils
Superconducting CMS
Solenoid Design
Charge and Momentum
CMS at CERN
S = Solenoid!
CMS Muon Chambers
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
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
All silicon sensors:
pixel/strip tracking
“imaging” calorimeter
using tungsten with Si
wafers
Fixed Target Spectrometers
•Fixed target experiments study what happens when a
beam of particles smashes into the atoms of a target.
•Most beam energy goes into target recoil, a fraction
left to create new particles
•Particles produced, or scattered, generally fly forwards
•Detectors are typically cone-shaped, and placed
downstream of the beamline.
Fixed Target Experiments
If we think of collider experiments as power
tools for a broad range of discoveries, we can think
of fixed-target experiments as a set of scalpels
to dissect particular particles and processes.
The machine tool versus the surgeon's knife.
 - particle
Atom
Rutherford’s discovery of
the nucleus pioneered
fixed-target experiments.
b
impact
parameter
Later such experiments
found partons, and have
continued to illuminate
particle physics.
Probing the Structure of Matter
SLAC Endstation A:
Electrons on nucleons
Probing the Structure of Matter
Kinematic reach is physical:
Need to arrange spectrometer
According to physics desired
Polarized target material:
Frozen NH3 and ND3
Secondary Beam Particles
KTeV:
Kaons
at the
TeVatron
The KTeV
experiment
was
designed to
search for
direct CP
violation in
K -> 2 pion
decays, and
to study a
wide variety
of rare KL
decays.
Studying Secondary Particles
Studying Secondary Particles
Intense beam of K0s created from TeV energy protons
Using Secondary Beams as Probes
NuTeV: Neutrinos at the Tevatron
DIS
•Ten sq ft on the face, 120 ft long
•690 tons of steel, 84 scintillator boxes in target cal
•Toroidal magnetic field
•Muon drift chambers
Structure of Nucleon,
and sin2w
Neutrino Target & Product Detector
Using Secondary Beams as Probes
Charged Current
CC Interaction
   q  -  X
NC /CC  sin 2  w
Neutral Current
NC Interaction
  q    X
Secondary Beams as Probes
Fundamental Measurements
Next time… Discussion of measurement of fundamental
parameters in particle physics.
Fundamental Measurements
Charge: Charge of a particle can be determined two ways
1) Direction of deflection in a magnetic field
2) Charge-dependent quantity, such as ionization energy loss
Mass: