Polarized source performance and developments at Jefferson Lab

Strange-Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment

“…We used a 40 A polarized electron beam with an energy of 3:031 0:001 GeV over the measurement period of 700 h. It was generated with a strained GaAs polarized source [10] with 32 ns pulse timing (rather than the standard 2 ns) to allow for time-of-flight (TOF) measurements. The average beam polarization, measured with a Møller polarimeter [11] in interleaved runs, was 73:7 1:0%.…”

Measurements of the neutron electric to magnetic form factor ratioGEn/GMnvia thePlaster1, Semenov2, Aghalaryan3 et al. 2006Phys. Rev. C

“…The scattering asymmetries measured in our polarimeter were on the order of a few percentages. Polarized electrons were produced at the accelerator source via optical illumination of a strained GaAs photocathode (GaAs on GaAsP [55]) with circularly polarized laser light from a ∼500 mW Ti-sapphire laser [55,56]; the linearly polarized light from the laser was circularly polarized with a Pockels cell. The helicity of the circularly polarized light emerging from the Pockels cell was flipped at a frequency of 30 Hz (by switching the polarity of the high voltage applied to the Pockels cell) according to a pseudorandom scheme in which the helicity of one 33.3-ms window was randomly chosen, and the helicity of the following 33.3-ms window required to be that of the opposite helicity (i.e., a sequence of such "helicity pairs" could have been +−, −+, −+, +−, etc.).…”

Measuring the Weak Charge of the Proton and the Hadronic Parity Violation of the N → Δ Transition

“…Circularly polarized laser light strikes the photocathode and electrons are emitted via the photoelectric effect. The resulting longitudinal polarization is routinely greater than 85% [29,31].…”