Naslov
The Qweak experimental apparatus

Autori
Allison, T. ; Anderson, M. ; Androić, Darko ; ... ; Ševa, Tomislav ; ... ; Šimičević, Neven ; ... ; Zielinski, R.B.

Izvornik
Nuclear Instruments and Methods Physics Research Section A (0168-9002) 781 (2015); 105-133

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Parity violation; Electron scattering; Liquid hydrogen target

Sažetak
The Jefferson Lab QweakQweak 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 View the MathML sourcee→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 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 determined using dedicated low-current View the MathML source(~100pA) measurements with a set of drift chambers before (and a set of drift chambers and trigger scintillation counters after) the toroidal magnet.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

Napomena
Q-weak kolaboracija.

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