M. S. Lubell

A source of highly polarized electrons at the stanford linear accelerator center

Abstract A polarized electron source based upon photoionization of a state-selected 6 Li atomic beam has been developed as an injection gun for the Standford two-mile electron linear accelerator. The source (PEGGY) produces a pulsed beam of electrons with a maximum intensity of 2.6×10 9 electrons per pulse, a polarization of 0.85, a pulse length of 1.6 μs, and a repitition rate of 180 pulses/s. Since its installation at SLAC in July 1974, PEGGY has been used in several energy electron-nucleon scattering experiments.

Application of a dc Fano effect polarized electron source to low-energy electron-atom scattering.

A polarized electron source based upon the photoionization of unpolarized Cs atoms by circularly polarized light (Fano effect) has been developed and applied to the study of spin dependence in low-energy electron-atom scattering. Electron intensities of 10 nA with polarizations of 0.63+/-0.03 have been obtained routinely during continuous runs of up to 75 h. Frequent optical reversal of the direction of the longitudinal electron polarization minimizes systematic effects so that helicity dependent electron-scattering asymmetries smaller than 4 x 10(-4) can be measured.

Internal spin structure of the proton from high energy polarized e-p scattering

A review is given of our experimental knowledge of the spin dependent structure functions of the proton, which is based on inclusive high energy scattering of longitudinally polarized electrons by longitudinally polarized protons in both the deep inelastic and resonance regions, and includes preliminary results from our most recent SLAC experiment. Implications for scaling, sum rules, models of proton structure, and the hyperfine structure interval in hydrogen are given. Possible future directions of research are indicated.

Operating Experience with the Polarized Electron Gun at SLAC

During the two years of operation of the SLAC Polarized Electron Gun (PEGGY), the electron intensity delivered to the target has increased from 7 x 10/sup 7/ e/sup -//pulse to 1 x 10/sup 9/ e/sup -//pulse. The polarization is 0.85 with no measurable degradation caused by acceleration through the linear accelerator. The predominant cause of downtime is replenishment of lithium, which now averages 43 hours. The lifetime of a lithium load is about 175 hours.

Measurement of the internal spin structure of the proton

Our final results of measurements at SLAC of the spin dependent asymmetry in the deep inelastic scattering of longitudinally polarized electrons by longitudinally polarized protons are presented. Data were obtained at a scattering angle of 10° and for incident energies of 16.2 and 22.7 GeV, which cover the kinematic range 0.18<x<0.70 and 3.5<Q2<10.0 (GeV/c)2. We compare our results with various models of proton spin structure and with the Bjorken and Ellis‐Jaffe sum rules.

A Search for Parity Violation in the Inelastic Scattering of Polarized Electrons from Deuterium at 19.4-GeV

A search for partity violating effects in the inelastic scattering of polarized electrons off an unpolarized deuterium target at 19.4 GeV has recently been performed at SLAC. Using the 20‐GeV/c and 8‐GeV/c spectrometers, two kinematical points with Q2 values of 1.2 GeV/c2 and 4.2 GeV/c2, respectively, were measured. Statistical accuracy of the measurements approaches the level of the weak interactions. Systematic errors and the present status of the data analysis are discussed.