The physics of RHIC spin

We have started a program of colliding polarized protons in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven. This is the first polarized proton collider. We plan to probe the spin structure of the proton with strongly interacting probes, polarized quarks and gluons, to complement work with polarized lepton probes which observed that only 25% of the proton spin is carried by quarks and anti-quarks. We will also use parity violation to search for new physics, such as quark substructure or a Z' boson. The collider is unique. We will be probing QCD with a completely new tool.