Precise Measurement of the Weak Charge of the Proton - the Qweak Experiment.
by
48-224 - Madrone
SLAC
The Qweak experiment at Jefferson Laboratory made a direct determination of the proton’s weak charge via a precise measurement of the parity-violating asymmetry in elastic electron-proton scattering at a low four-momentum transfer. A longitudinally polarized electron beam was scattered off a liquid hydrogen target and detected in eight azimuthally symmetric fused silica detectors. The parity violation asymmetry was measured by observing the difference in scattering rates when the helicity of the electron beam was rapidly reversed. The result was published in 2018, with a measured asymmetry of − 226.5 ± 7.3 ( stat ) ± 5.8 ( syst ) ppb. When combined with previous parity-violating electron scattering (PVES) data, we obtained a value for weak charge of proton, 0.0719 ± 0.0045, which agrees well with the prediction of Standard Model.
Alden Fan / Christina Ignarra