From Elastic Scattering to Central Exclusive Production: Physics with Forward Protons at RHIC

We describe a physics program at the Relativistic Heavy Ion Collider (RHIC) with tagged forward protons. The program started with the proton–proton elastic scattering experiment (PP2PP), for which a set of Roman Pot stations was built. The PP2PP experiment took data at RHIC as a dedicated experiment at the beginning of RHIC operations. To expand the physics program to include non-elastic channels with forward protons, such as Central Exclusive Production (CEP), Central Production (CP) and Single Diffraction Dissociation (SD), the experiment with its equipment was merged with the STAR experiment at RHIC. Consequently, the expanded program, which included both elastic and inelastic channels became a part of the physics program and operations of the STAR experiment. In this paper, we shall describe the physics results obtained by the PP2PP and STAR experiments to date.