Forward Meson Production and Spin Asymmetries at RHIC

Proton high energy structure and the high energy proton-proton interaction depend on the spin and angular momentum of the underlying quarks and gluons. Unique tools are available at the Brookhaven Relativistic Heavy Ion Collider (RHIC), which make it possible to study the role of the spin of the proton constituents in polarized proton collisions. RHIC is the first high energy polarized proton collider, where experimentalists can prepare the spin orientation of high energy protons before they collide. These polarized proton collisions are studied in the STAR detector with center of mass energies up to 500 GeV. When relativistic protons collide, they produce high energy fragments including neutral pions, etas and jets of particles. It is in the very forward region where particle production is most sensitive to the orientation of the proton spin. This research involves measurement of forward fragments in relativistic proton-proton collisions. In particular, transverse spin dependence is studied using a lead-glass calorimeter called the FMS, which is located in the forward region of the STAR detector. The goal is to characterize the dependence of this production on event kinematics. We test QCD related predictions of how the spin of the proton correlates with the spin of quarks and how this can modify the observable cross sections. This grant supports the collection of new RHIC FMS data and the analysis of that data. The objective is better understanding of the most basic questions about the nature of the proton.

The proton is understood to consist of quarks and gluons bound together by the strong force. This project investigates the role quark spin plays in the structure of the proton. This investigation involves the construction and ongoing operation of the FMS calorimeter in the STAR detector at Brookhaven National Lab. The FMS apparatus is available to all the other collaborators in STAR. The over 500 STAR collaborators work on a diverse range of physics topics, many of which are enhanced by the presence of the FMS. This research involves participation of undergraduate students who assist in fabrication of electronics and in analysis of data from the experiment. It involves graduate students, both those supported by this grant and others who use our apparatus. We also introduce interested middle school or high school students to our work and involve them where possible.