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Quartz Scanner for Qweak. Jeff Martin University of Winnipeg. Motivation. Q 2 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.
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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 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
scattered beam Č Principle of E158 Scanner • For E158, PMT operated in current mode. pre-rad quartz PMT
E158 as-built 19 mm tube
scattered beam Č Č 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 pre-rad PMT PMT quartz 2” air-core light guide
Implementation in Qweak • 2D motion assy scans over surface of Č-bar • Mount on Region III rotating support structure in unused octant.
Expected rates at 180 A courtesy J. Mammei • Max rate = 1 MHz
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.