Measurements of {Delta}{sigma}{sub L}(pp) and {Delta}{sigma}{sub L}({bar p}p) at 200 GeV/c

A measurement was made at Fermilab of the difference in the total cross sections between states with beam and target polarizations aligned antiparallel and parallel, {Delta}{sigma}{sub L} = {Delta}{sigma}({r_reversible}) - {Delta}{sigma}({R_arrow}), using 200-GeV/c, polarized proton and antiproton beams and a polarized proton target. This measurement explores the spin dependence of particle interactions and the constituent dynamics. A difference in the spin-dependent total cross sections has been observed in previous experiments at lower energies, and this experiment was the first to explore possible spin effects in {Delta}{sigma}{sub L} at much higher energies. The polarized proton beam is produced from parity-nonconserving decays of the {Lambda}{sup 0} hyperon, where protons emitted from these decays have their spins aligned along the direction of their momenta. The {Lambda} hyperons are produced, along with other particles, when unpolarized, 800-GeV/c protons strike a beryllium target. A virtual source of protons is produced at the target from these decays and the proton polarization is correlated to the transverse distance from the target. A beam of polarized antiprotons can be produced in an analogous manner using {bar {Lambda}{sup 0}} decays. The beam transport system goal was to produce no net spin precession and to preserve the correlation between the beam particle polarization and the transverse position at the virtual source. The beam transport used four sets of quadrupole magnets to focus the beam at intermediate and final focal points. An electronic, particle-tagging system was located at the intermediate focus, while the polarized target was near the final focus