Eur. Phys. J. A 24, s2.159-s2.160 (2005)
DOI: 10.1140/epjad/s2005-04-040-0

The Qweak tracking system

Measurement of the average Q² and the dilution by background events

Klaus H. Grimm

The College of William & Mary, Department of Physics, Williamsburg, VA 23187-8795, USA

(Received 01 November 2004 / Published online 08 February 2005)

Abstract

The Q_weak^p experiment will measure the parity-violating elastic e-p scattering asymmetry to extract the weak charge of the proton. The experiment employs a toroidal magnet to focus electrons scattered at 8^o ± 2^o, corresponding to Q² ~ 0.03 (GeV/c)², on eight Cerenkov detectors located in the focal plane of the spectrometer. Since the asymmetry is proportional to Q², it is crucial to obtain an accurate measure of the acceptance-averaged value of Q². A tracking system will be used in a low-rate counting mode, allowing individual events to be observed. This will enable a determination of the average Q² by measuring the scattering angle and interaction vertex, for mapping the response across the surface of the Cerenkov detectors, and for the dilution of the Cerenkov detector signal by background.

PACS: 25.30.Bf Elastic electron scattering - 29.40.Gx Tracking and position-sensitive detectors

The Author, for the Qweak Collaboration

© Società Italiana di Fisica, Springer-Verlag 2005