Quartz Scanner for Qweak
Jeff Martin
University of Winnipeg
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.
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.
E158 Scanners
beam’s eye
view
• 4 scanners
• radial and
azimuthal motion
E158 Scanner Impact
from first E158 PRL
ee
ep
validation of MC results and hence dilutions
Principle of E158 Scanner
scattered beam
pre-rad
Č
quartz
PMT
• For E158, PMT operated in current mode.
E158 as-built
19 mm tube
Qweak Scanner
scattered beam
pre-rad
PMT
Č
Č
quartz
2” air-core light guide
• Always operate in pulse-counting mode, use 2” tubes.
• Coincidence requirement to reduce background from light
guides.
• V-shape to fit in Qweak
PMT
Implementation in Qweak
• 2D motion assy scans over surface of Č-bar
• Mount on Region III rotating support
structure in unused octant.
Implementation in Qweak
Implementation in Qweak
Implementation in Qweak
Implementation in Qweak
Implementation in Qweak
• Expected rates at 180 A
• Max rate = 1 MHz
courtesy
J. Mammei
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.
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.
light yield simulation
quartz, 1 cm thick
air-core
lightpipe
30 p.e. per tube with no preradiator.
Order of magnitude agreement with
E158 simulations
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.