Quartz Scanner for Qweak

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Quartz Scanner for Qweak

• Jeff Martin
• University of Winnipeg

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Motivation

• Q2 determination, background studies, all done at
  10 nA using tracking system.
• Region III operable up to 100 nA.
• Qweak production running 180 ?A.
• Need a way to extrapolate over 3 orders of
  magnitude.

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Proposal

• Construct a scanning detector with small active
  area to sense high-energy electrons and operable
  at any beam current.
• Similar technique used in E158 and HAPPEx.
• For E158, it was used to determine optics
  parameters, confirm Monte Carlo predictions of
  rates.

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E158 Scanners
beams eye view

• 4 scanners
• radial and azimuthal motion

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E158 Scanner Impact
from first E158 PRL
ee
ep
validation of MC results and hence dilutions
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Principle of E158 Scanner
pre-rad
quartz
PMT

• For E158, PMT operated in current mode.

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E158 as-built
19 mm tube
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Qweak Scanner
pre-rad
PMT
PMT
2 air-core light guide
quartz

• Always operate in pulse-counting mode, use 2
  tubes.
• Coincidence requirement to reduce background from
  light guides.
• V-shape to fit in Qweak

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Implementation in Qweak

• 2D motion assy scans over surface of C-bar
• Mount on Region III rotating support structure in
  unused octant.

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Implementation in Qweak
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Implementation in Qweak
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Implementation in Qweak
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Implementation in Qweak
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Implementation in Qweak
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• Expected rates at 180 ?A

courtesy J. Mammei

• Max rate 1 MHz

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Procedure

• Measure light distribution with scanner at low
  beam current acceptable to region III and
  Cherenkov bar coincidence.
• Measure light distribution with scanner at 180
  uA.
• If they are the same, region III/Cherenkov light
  distribution believable at 180 uA to high
  confidence.
• Note scanner light map will not be the same as
  the region III/Cherenkov bar coincidence map.

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Additional Uses of a Scanner Detector

• 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
• mini-torus setting during production running?
• gas vs. liquid target extrapolation?
• at least, complementary to region III.

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light yield simulation
quartz, 1 cm thick
air-core lightpipe
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30 p.e. per tube with no preradiator. Order of
magnitude agreement with E158 simulations
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Plan

• Conduct light yield simulations.
• Benchmark with lab tests.
• Work on implementation in Qweak.
• Proposal to NSERC due Oct. 25, 2005, comments
  received from Davis, Mack, Pitt, Page, van Oers.
  Funding decision April 1, 2006.
• Simultaneous proposal to CFI for detector lab
  infrastructure at UWinnipeg.