Focal Plane Scanner for Qweak Experiment

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Focal Plane Scanner for Qweak Experiment
Jie Pan Directed by Prof. Jeff Martin _at_
University of Winnipeg
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Running of Weak Mixing Angle
Qweaks goal error bar
Standard model prediction sin2?w varies with
momentum transfer Q of high energy colliders
called running of weak mixing angle
SLAC E158
Standard Model Prediction Erler,. Phys. Rev. D68,
016006 (2003)
In experiment, all extracted values of
sin2?must agree with the Standard model
prediction, or new physics is indicated!!
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Qweak Experiment
Using Parity Violation as a tool to precisely
measure the parity-violating asymmetry in
electron-proton scattering to infer protons weak
charge. 
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Qweak Main Detector
CERENKOV EFFECT The Cerenkov electromagnetic
radiation, usually bluish light, is emitted by a
beam of high-energy charged particles passing
through a transparent medium at a speed greater
than the speed of light in that medium.
Beam eye view
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Focal Plane Scanner
C-bar
y-axis motion
x-axis motion
A scanning Cherenkov detector mounted on the
focal plane with very small active area to sense
high-energy electrons and operable at any beam
current.
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Scanner Principle
pre-rad
scattered electrons
quartz radiator
C
scattered electrons
air-core light pipe
side view
PMT

• Design criteria
• Small (1 cm2) active area.
• 1 MHz max rate allows operation in counting mode
  with two PMTs.
• operable at both high and low current.
• coincidence

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Procedure in Experiment

• Procedure
• Measure light distribution with scanner at low
  beam current acceptable to region III and
  Cherenkov bar coincidence, then measure light
  distribution with scanner at 180 µA. If they are
  the same, region III/Cherenkov light distribution
  believable at 180 uA to high confidence.
• Additional uses
• Scan over large fiducial region, into inelastic
  region, over Cherenkov bar light guides, to get
  additional confidence in backgrounds.
• Light map can be compared to simulation.
• Q2 extrapolation/determination
• Determine optics parameters, confirm Monte Carlo
  predictions of rates, etc.

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Monte Carlo simulation for Scanner Performance
Pre-radiator
Cherenkov detector (fused silica)
Electron
Cascade developed in pre-rad
Air-core light pipe
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Simulation Work in Progress
Geometry definition in GEANT4
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Cosmic Ray Test
muon
MCA reads out shaped pulse height
upper trigger
test detector
a small test scintillator (inside Alzak tube)
lower trigger
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Mechanics

• To-dos
• Answer prototyping/simulation questions
• radiator design (quartz? scint? size? tilt angle?
  prerad?)
• tube diameter (backgrounds)
• two-tube layout (backgrounds and fiducial area)
• establish viability of coincidence technique
  (rates)
• Mechanics
• Build the support structure
• Get 2D motion assembly and program it.
• Design and build a mechanical mock-up of detector
  assembly and then a realistic detector

• Support structure
• 2D motion assembly
• Detector assembly

MIRO 2
Anomet
Air core light guide
3D SolidWorks Model