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 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. PMT quartz pre-rad scattered 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 ČČ

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

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. Q 2 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, Simultaneous proposal to CFI for detector lab infrastructure at UWinnipeg.