Understanding the Proton’s Spin at STAR

Document Type

Conference Proceeding

Publication Date



A major goal of the proton spin physics program at the Relativistic Heavy Ion Collider (RHIC) is to constrain the gluon polarization distribution Δg(x) and thus determine the contribution of gluons to the spin of the proton. Recent global analyses, with major impact from STAR, have demonstrated a positive contribution to the spin of the proton from mid-to-high x gluons (e.g. x>0.05). A variety of measurements at STAR have been recently completed, or are now underway, to better constrain the gluon polarization distribution, particularly at low x. Inclusive jet measurements at mid-rapidity (tracking with |η|<1.3) remain a core part of the STAR program while measurements with correlated observables like dijets provide more precise information about the initial-state parton kinematics. Moving to forward pseudorapidities (additional calorimetry with 1.09<η<2.00 and 2.65<η<4.0) with neutral pions allows us to probe lower partonic momenta, as does moving to higher center-of-mass energy. We will present the status of a variety of asymmetry measurements and the results of others using jet, dijet and neutral pion probes with longitudinally polarized p+p datasets at s√=200 GeV (25 pb−1) and s√=510 GeV (382 pb−1).