Triple GEM detectors : Beam monitoring for beam profile and intensity measurements.
Detectors & Measurements II: How we do physics without seeing…
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Transcript of Detectors & Measurements II: How we do physics without seeing…
Detectors & Measurements II: Detectors & Measurements II: How we do physics without seeing…How we do physics without seeing…
Prof. Robin D. ErbacherUniversity 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, …
Overview of Detectors and Fundamental Measurements:From Quarks to Lifetimes
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:
• helical trajectory deviates due to radiation E losses, spatial inhomogeneities in B field, multiple scattering, ionization
• Approximately:
€
dp
dt=
q
cv × B
€
p = 0.2998Bρ T - m
€
ρ = radius of curvature
Magnets for 4 DetectorsSolenoid 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
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 sensors6,136 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” calorimeterusing 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
impactparameter
b
Rutherford’s discovery of the nucleus pioneered fixed-target experiments.
Later such experiments found partons, and have continued to illuminate particle physics.
Probing the Structure of Matter
Kinematic reach is physical:Need to arrange spectrometerAccording 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.
Using Secondary Beams as Probes
NuTeV: Neutrinos at the Tevatron
•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
DIS
Structure of Nucleon, and sin2w
Using Secondary Beams as Probes
Charged CurrentCC Interaction
€
ν μ + q →ν μ + X
Neutral CurrentNC Interaction
€
ν μ + q → μ− + X
€
NC /CC ⇒ sin2 θw
Fundamental Measurements
Next time… Discussion of measurement of fundamental parameters in particle physics.