The Q sub(weak) experimental apparatus

The Jefferson Lab experiment determined the weak charge of the proton by measuring the parity-violating elastic scattering asymmetry of longitudinally polarized electrons from an unpolarized liquid hydrogen target at small momentum transfer. A custom apparatus was designed for this experiment to mee...

Full description

Saved in:

Bibliographic Details
Published in:	Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 781; pp. 105 - 133
Main Authors:	Allison, T, Anderson, M, Androic, D, Armstrong, D S, Asaturyan, A, Averett, T, Averill, R, Balewski, J, Beaufait, J, Beminiwattha, R S, Benesch, J, Benmokhtar, F, Bessuille, J, Birchall, J, Bonnell, E, Bowman, J D, Brindza, P, Brown, D B, Carlini, R D, Cates, G D, Cavness, B, Clark, G, Cornejo, J C, Dusa, SCovrig, Dalton, M M, Davis, CA, Dean, D C, Deconinck, W, Diefenbach, J, Dow, K, Dowd, J F, Dunne, JA, Dutta, D, Duvall, W S, Echols, J R, Elaasar, M, Falk, W R, Finelli, K D, Finn, J M, Gaskell, D, Gericke, MTW, Grames, J, Gray, V M, Grimm, K, Guo, F, Hansknecht, J, Harrison, D J, Henderson, E, Hoskins, J R, Ihloff, E, et. al
Format:	Journal Article
Language:	English
Published:	01-05-2015
Subjects:	Asymmetry Beams (radiation) Detectors Drift Helicity Liquid hydrogen Momentum transfer Polarimetry
Online Access:	Get full text
Tags:	Add Tag No Tags, Be the first to tag this record!

Description
Summary:	The Jefferson Lab experiment determined the weak charge of the proton by measuring the parity-violating elastic scattering asymmetry of longitudinally polarized electrons from an unpolarized liquid hydrogen target at small momentum transfer. A custom apparatus was designed for this experiment to meet the technical challenges presented by the smallest and most precise asymmetry ever measured. Technical milestones were achieved at Jefferson Lab in target power, beam current, beam helicity reversal rate, polarimetry, detected rates, and control of helicity-correlated beam properties. The experiment employed 180 mu A of 89% longitudinally polarized electrons whose helicity was reversed 960 times per second. The electrons were accelerated to 1.16 GeV and directed to a beamline with extensive instrumentation to measure helicity-correlated beam properties that can induce false asymmetries. Moeller and Compton polarimetry were used to measure the electron beam polarization to better than 1%. The electron beam was incident on a 34.4 cm liquid hydrogen target. After passing through a triple collimator system, scattered electrons between 5.8 degree and 11.6 degree were bent in the toroidal magnetic field of a resistive copper-coil magnet. The electrons inside this acceptance were focused onto eight fused silica Cherenkov detectors arrayed symmetrically around the beam axis. A total scattered electron rate of about 7 GHz was incident on the detector array. The detectors were read out in integrating mode by custom-built low-noise pre-amplifiers and 18-bit sampling ADC modules. The momentum transfer Q super(2)=0.025 GeV super(2) was determined using dedicated low-current measurements with a set of drift chambers before (and a set of drift chambers and trigger scintillation counters after) the toroidal magnet.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 content type line 23 ObjectType-Feature-2
ISSN:	0168-9002
DOI:	10.1016/j.nima.2015.01.023