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.