Recent results on cold-QCD from RHIC

Qinghua Xu

doi:10.1051/epjconf/202023503002

Abstract

Polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) provide unique opportunities to study the spin structure of the nucleon. We will highlight recent results on the nucleon spin structure from the STAR and PHENIX experiments at RHIC: (1) A sizable gluon polarization in the proton is measured with longitudinal double spin asymmetries of jet and hadron production; (2) Longitudinal single spin asymmetries in W boson production improve constraints on the sea quark polarization. The new spin asymmetry results for W boson confirmed the SU(2) flavor asymmetry of the light sea quark polarization in the proton; (3) Transverse spin effects in hadronic systems offer new implications on parton distribution functions in the collinear and transverse momentum dependent frameworks. We will also discuss near term plans for the STAR forward detector upgrade and prospects for proton-proton and protonion collisions in the years beyond 2021 at STAR.

Highlights

Introduction to Relativistic Heavy Ion Collider (RHIC) spin programIn addition to colliding heavy ions, RHIC at Brookhaven National Laboratory is the world’s only polarized proton-proton collider
RHIC continues its efforts to deepen our understanding of the nucleon spin structure
Sizable gluon polarization in the proton has been determined from RHIC measurements with polarized proton beams

Summary

Introduction to RHIC spin program

In addition to colliding heavy ions, RHIC at Brookhaven National Laboratory is the world’s only polarized proton-proton (pp) collider. By colliding high-energy beams of polarized protons, RHIC provides unique opportunities for exploring the spin structure of the proton [1]. The results from polarized Deep-Inelastic-Scattering (DIS) experiments in the past 30 years have shown that the spins of the quarks and antiquarks account for only about 30% of proton’s spin in the measured x-range. Since 2001, RHIC has been providing pp collisions at center of mass energies of 200 GeV and 500 GeV with beams longitudinally or transversely polarized. There have been two main detectors, PHENIX and STAR, at RHIC to perform spin experiments as well as heavy ion ones. We will discuss future plans for the STAR forward detector upgrade and prospects for pp and proton-ion (pA) collisions in the years beyond 2021 at RHIC

Recent highlights from RHIC spin

Probing sea quark polarization via W boson production

Transverse spin physics results

Summary and future plan for cold-QCD physics at RHIC