Large Rapidity Polarized Proton Measurements and Gluon Nuclear Saturation Effects at STAR

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We have built and we will upgrade electromagnetic calorimeters for thevery forward region of the STAR detector at Brookhaven National Lab. Itis well known that when energetic particles are produced at large anglesto the incident beam axis (at high transverse momentum), the underlyingprocess involves scattering between pairs of individual quarks or gluons.However, scattering that produces energetic particles at forward angles,relative to the beam axis, is likely to involve the interaction of asingle high energy quark with one or more low energy gluons. Measurementsof these forward processes are important to understand how a single fastquark interacts with a soft multi-gluon field. From general arguments,saturation of these gluon fields is expected to occur when the number ofparticipating gluons is large. Theoretical models predict such effects.Comparisons will be made between pp scattering and dAu scattering forproduction of forward hadrons.A similar pp measurement, with one proton polarized in a directiontransverse to the beam (up), leads to a left-right asymmetry in theforward cross section. We plan new measurements of this asymmetry, withdetailed characterization of the correlated particle production that willdistinguish between models that require initial state quark orbitalangular momentum from models that involve the fragmentation of highlypolarized quarks into final state jet fragments. The resolution of thisquestion is an important step in understanding the roles of spin andangular momentum for proton constituents.