From Elastic Scattering to Central Exclusive Production in Proton–Proton Collisions at RHIC

We describe the physics program at the Relativistic Heavy Ion Collider (RHIC) with forward protons measured in the Roman Pot system. The program started as a standalone PP2PP experiment with a goal of measuring of proton–proton elastic scattering. 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. This allowed for a more comprehensive diffractive physics program with measured forward protons. The expanded program, which included both elastic and inelastic proton–proton scattering, became part of the physics program and operations of the STAR experiment. The results obtained by both programs are described here. Given that proton beams at RHIC were polarized, the results include spin dependence in proton–proton elastic scattering. Abstract Published by the Jagiellonian University 2026 authors