The Qweak 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 created 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 μA 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. Møller 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° and 11.6° 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 Q2=0.025 GeV2 was observed 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
- Research Organization:
- Mississippi State Univ., Mississippi State, MS (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP); Natural Sciences and Engineering Research Council of Canada (NSERC); Canada Foundation for Innovation; National Science Foundation (NSF)
- Contributing Organization:
- The Qweak Collaboration
- Grant/Contract Number:
- FG02-07ER41528; AC05-06OR23177; PHY-0320942, PHY-0321197; PHY-0320759; PHY-0320832
- OSTI ID:
- 1599859
- Alternate ID(s):
- OSTI ID: 1246544
- Journal Information:
- Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 781, Issue C; ISSN 0168-9002
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
The P2 experiment: A future high-precision measurement of the weak mixing angle at low momentum transfer
|
journal | November 2018 |
Precision measurement of the weak charge of the proton
|
journal | May 2018 |
The P2 Experiment - A future high-precision measurement of the electroweak mixing angle at low momentum transfer | text | January 2018 |
Precision Measurement of the Weak Charge of the Proton | text | January 2019 |
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