Recent highlights of cold QCD physics at RHIC*

The exploration of the fundamental structure of strongly interacting matter has always thrived on the complementarity of lepton scattering and purely hadronic probes. As the community eagerly anticipates a future electron-ion collider (EIC) in the U.S., an outstanding scientific opportunity remains to complete “must-do” measurements in p+p and p+A physics in the years preceding the EIC. The unique capability of Relativistic Heavy Ion Collider (RHIC) to provide both longitudinally and transversely polarized hadronic collisions at various energies has opened new avenues for studying the internal structure of the proton with unprecedented depth and precision. A remarkable breadth of physics results has been produced from the RHIC Cold QCD program over the past two decades.

In this talk, I will present the highlights of longitudinal and transverse spin, as well as the unpolarized physics conducted at RHIC to date. These measurements are essential for fully realizing the scientific missions of the EIC by providing a comprehensive set of measurements in hadronic collisions. By combining the data from RHIC and the EIC, we can establish the validity and limits of factorization and universality. Additionally, while much of the physics in this program is unique to p+p and p+A collisions and offers discovery potential on its own, when combined with data from the EIC, it will provide a broad foundation for a deeper understanding of fundamental QCD.