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20 April 2024

» arxiv » 1409.7100

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The Q_weak Experimental Apparatus
Qweak Collaboration ; T. Allison ; M. Anderson ; D. Androic ; D.S. Armstrong ; A. Asaturyan ; T.D. Averett ; R. Averill ; J. Balewski ; J. Beaufait ; R.S. Beminiwattha ; J. Benesch ; F. Benmokhtar ; J. Bessuille ; J. Birchall ; E. Bonnell ; J. Bowman ; P. Brindza ; D.B. Brown ; R.D. Carlini ; G.D. Cates ; B. Cavness ; G. Clark ; J.C. Cornejo ; S. Covrig Dusa ; M.M. Dalton ; C.A. Davis ; D.C. Dean ; W. Deconinck ; J. Diefenbach ; K. Dow ; J.F. Dowd ; J.A. Dunne ; D. Dutta ; W.S. Duvall ; J.R. Echols ; M. Elaasar ; W.R. Falk ; K.D. Finelli ; J.M. Finn ; D. Gaskell ; M.T.W. Gericke ; J. Grames ; V.M. Gray ; K. Grimm ; F. Guo ; J. Hansknecht ; D.J. Harrison ; E. Henderson ; J.R. Hoskins ; E. Ihloff ; K. Johnston ; D. Jones ; M. Jones ; R. Jones ; M. Kargiantoulakis ; J. Kelsey ; N. Khan ; P.M. King ; E. Korkmaz ; S. Kowalski ; A. Kubera ; J. Leacock ; J.P. Leckey ; A.R. Lee ; J.H. Lee ; L. Lee ; Y. Liang ; S. MacEwan ; D. Mack ; J.A. Magee ; R. Mahurin ; J. Mammei ; J.W. Martin ; A. McCreary ; M.H. McDonald ; M.J. McHugh ; P. Medeiros ; D. Meekins ; J. Mei ; R. Michaels ; A. Micherdzinska ; A. Mkrtchyan ; H. Mkrtchyan ; N. Morgan ; J. Musson ; K.E. Mesick ; A. Narayan ; L.Z. Ndukum ; V. Nelyubin ; Nuruzzaman ; W.T.H. van Oers ; A.K. Opper ; S.A. Page ; J. Pan ; K.D. Paschke ; S.K. Phillips ; M.L. Pitt ; M. Poelker ; J.F. Rajotte ; W.D. Ramsay ; W.R. Roberts ; J. Roche ; P.W. Rose ; B. Sawatzky ; T. Seva ; M.H. Shabestari ; R. Silwal ; N. Simicevic ; G.R. Smith ; S. Sobczynski ; P. Solvignon ; D.T. Spayde ; B. Stokes ; D.W. Storey ; A. Subedi ; R. Subedi ; R. Suleiman ; V. Tadevosyan ; W.A. Tobias ; V. Tvaskis ; E. Urban ; B. Waidyawansa ; P. Wang ; S.P. Wells ; S.A. Wood ; S. Yang ; S. Zhamkochyan ; R.B. Zielinski ;
Date:	24 Sep 2014
Abstract:	The Jefferson Lab Q_weak 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 ${vec{e}}$p 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 microA 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. Moller 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 degrees and 11.6 degrees were bent in the toroidal magnetic field of a resistive copper-coil magnet. The electrons inside this acceptance were focused onto eight fused silica Cerenkov 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^2 = 0.025 GeV^2 was determined using dedicated low-current (~100 pA) measurements with a set of drift chambers before (and a set of drift chambers and trigger scintillation counters after) the toroidal magnet.
Source:	arXiv, 1409.7100
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