Charged-pion cross sections and double-helicity asymmetries in polarized p+p collisions at sqrt[s]=200 GeV

We present midrapidity charged-pion invariant cross sections, the ratio of the π − to π + cross 125 sections and the charge-separated double-spin asymmetries in polarized p + p collisions at √ s = 126 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading- 127 order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations over 128 estimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation 129 of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and 130 highlights the constraints these data will place on flavor dependent pion fragmentation functions. 131 The charge-separated pion asymmetries presented here sample an x range of ∼ 0.03–0.16 and provide 132 unique information on the sign of the gluon-helicity distribution. charged-pion cross section measurements in polarization-averaged p + p collisions and double- helicity asymmetry measurements in charged pion production in longitudinally polarized proton collisions at √ s 200 GeV. The cross section measurements provide information on charge-separated collinear FFs for pions; the spin asymmetry measurements are sensitive to the collinear helicity distributions in the proton. Improved knowledge of FFs can lead to improved knowledge of PDFs, and vice versa, in a continuous, iterative process of increasingly refined constraints on nonperturbative aspects of QCD. In Sec. II we describe the PHENIX experiment; Sec. III discusses the analysis; Sec. IV presents the results,