Single spin-asymmetry measurements in the inclusive production of pions and protons at high momentum transfer

This thesis reports the results of Brookhaven Experiment E785, which measured the effect of spin on the inclusive production of secondary particles in proton-proton collisions. By using a transversely polarized proton beam incident on an unpolarized hydrogen target, the analyzing power, A = (N↑ = αN↓)/(N↑ + αN↓), for three reactions: p ↑ +p → π+ + X; p ↑ +p → p + X; p ↑ → π- + X was measured at incident beam energy of 13.3 and 18.5 GeV/c. The asymmetry is consistent with zero for all data taken in the production of negative pions (π-) or protons. Large asymmetries were measured in π+ production. These asymmetries grow with transverse momentum, approaching values of 30% at high pt (pt ∼ 2.0 GeV/c). These asymmetries exhibit little if any dependence on Feynman x (xf). The data are found to scale with beam energy when expressed as a function of xt (xt = 2 pt /√s). These data are compared to a variety of theoretical models, none of which can explain the data. In particular the Perturbative Quantum Chromodynamics (PQCD) predicts no asymmetry at all, and the phenomenological Quark Fragmentation Recombination model (QFR) predicts Aπ+ = -2Aπ- = 4Aπ0. Several possible modifications to these theories--the inclusion of higher twist effects in PQCD, and the utilization wave function other than SU(6) for the proton--are discussed. Baryon exchange and Quantum Geodynamic approaches to hadron scattering and spin physics are considered