Recent Cold QCD Results from STAR

Abstract

Understanding the origin of transverse single-spin asymmetries is a long-standing challenge in strong interaction physics. Recent precise measurements of the azimuthal distribution of charged pions in jets from STAR have shed new light on the spin momentum correlations within the Transverse Momentum Dependent (TMD) formalism. This measurement, particularly sensitive to the Collins effect, correlates the quark transversity with the Collins fragmentation functions, elucidating the spin-dependent fragmentation process. Moreover, similar measurements involving kaons and protons, which have unique quark compositions, provide vital insights into the flavor-dependent spin dynamics of the parton distribution functions and fragmentation functions. These studies are crucial for developing a more comprehensive understanding of nucleon spin structure. In these proceedings, selection of the recent Cold QCD STAR results are presented, focusing on the asymmetries for charged kaons and protons in jets from transversely polarized $pp$ data at $\sqrt{s}$ = 200 GeV.

4 pages, 3 figures, Contribution to the Proceedings of the 58th Rencontres de Moriond session devoted to QCD AND HIGH ENERGY INTERACTIONS (Moriond QCD2024)