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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
• 4 scanners
• radial and azimuthal motion
beam’s eye view
E158 Scanner Impact
ep
ee
validation of MC results and hence dilutions
from first E158 PRL
Principle of E158 Scanner
• For E158, PMT operated in current mode.
PMTquartz
pre-radscattered beam
Č
E158 as-built
19 mm tube
Qweak Scanner
• Always operate in pulse-counting mode, use 2” tubes.• Coincidence requirement to reduce background from light
guides.• V-shape to fit in Qweak
2” air-core light guide
PMT
quartz
scattered beam
pre-rad
PMT Č Č
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 MHzcourtesyJ. 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 thickair-corelightpipe
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.
