Download or read book Inclusive Cross Section and Double-helicity Asymmetry for [math Display written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We present PHENIX measurements for the cross section and double-helicity asymmetry (ALL) in inclusive [pi]0 production at midrapidity from p + p collisions at √s = 510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. Our [pi]0ALL results follow an increasingly positive asymmetry trend with pT and √s with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on [pi]0 and jet ALL and suggested a positive contribution of gluon polarization to the spin of the proton [Delta]G for the gluon momentum fraction range x > 0.05. Finally, the data presented here extend to a currently unexplored region, down to x similar to 0.01, and thus provide additional constraints on the value of [Delta]G.