Exploring Nucleon Spin Structure in Longitudinally Polarized Collisions

We review how RHIC is expected to deepen our understanding of the spin structure of longitudinally polarized nucleons. After briefly outlining the current status of spin-dependent parton densities and pointing out open questions, we focus on theoretical calculations and predictions relevant for the RHIC spin program. Estimates of the expected statistical accuracy for such measurements are presented, taking into account the acceptance of the RHIC detectors.Comment: 10 pages, 7 figures, uses aipproc style, invited talk presented at the 15th International Spin Physics Symposium 'SPIN 2002', Sept. 9-14 2002, Brookhaven National Laboratory, Upton, N

Spin Physics at RHIC - a Theoretical Overview

We review how RHIC is expected to deepen our understanding of the spin structure of longitudinally and transversely polarized nucleons. After briefly outlining the current status of spin-dependent parton densities and pointing out open questions, we focus on theoretical calculations and predictions relevant for the RHIC spin program. Estimates of the expected statistical accuracy for such measurements are presented, taking into account the acceptance of the RHIC detectors.Comment: 13 pages, 8 figures, uses ws-procs9x6 style, invited talk presented at the workshop `Testing QCD through Spin Observables in Nuclear Targets', Charlottesville, VA, April 18-20, 200

Next-to-Leading Order QCD Corrections to Inclusive Heavy-Flavor Production in Polarized Deep-Inelastic Scattering

We report on a recently completed, first calculation of the full next-to-leading order QCD corrections for heavy flavor contributions to the inclusive structure function $g_1$ in longitudinally polarized deep-inelastic scattering. All results are derived with largely analytical methods and retain the full dependence on the heavy quark's mass. As a first phenomenological application, inclusive charm production at a future electron-ion collider and its sensitivity to the polarized gluon distribution is studied. Theoretical uncertainties due to the residual dependence on unphysical factorization and renormalization scales are estimated.Comment: 6 pages, 6 eps figures, XXVI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2018

Longitudinally Polarized Photoproduction of Heavy Flavors at Next-to-Leading Order of QCD

We present a phenomenological study of charm quark photoproduction in longitudinally polarized lepton-hadron collisions at next-to-leading order accuracy of QCD. Our results are based on a recently developed, flexible parton-level Monte Carlo program for spin-dependent heavy flavor hadroproduction, which we extend to deal also with both direct and resolved photon contributions. The subsequent hadronization into charmed mesons is modeled in our calculations, which allows us to compare with data on double-spin asymmetries for D0 meson production taken by the COMPASS collaboration. In general, next-to-leading order QCD corrections are found to be very significant and do not cancel in spin asymmetries. We elucidate the role of the individual hard scattering subprocesses and determine the range of parton momentum fractions predominantly probed for charm production at COMPASS. Theoretical uncertainties are estimated by varying renormalization and factorization scales and parameters controlling the hadronization of the charm quarks.Comment: 11 pages, 8 figure

Fragmentations Functions in Nuclear Media

We perform a detailed phenomenological analysis of how well hadronization in nuclear environments can be described in terms of effective fragmentation functions. The medium modified fragmentation functions are assumed to factorize from the partonic scattering cross sections and evolve in the hard scale in the same way as the standard or vacuum fragmentation functions. Based on precise data on semi-inclusive deep-inelastic scattering off nuclei and hadron production in deuteron-gold collisions, we extract sets of effective fragmentation functions for pions and kaons at NLO accuracy. The obtained sets provide a rather accurate description of the kinematical dependence of the analyzed cross sections and are found to differ significantly from standard fragmentation functions both in shape and magnitude. Our results support the notion of factorization and universality in the studied nuclear environments, at least in an effective way and within the precision of the available data.Comment: 17 pages, 11 figure

Global Analysis of Fragmentation Functions for Protons and Charged Hadrons

We present new sets of fragmentation functions for protons and inclusive charged hadrons obtained in combined NLO QCD analyses of single-inclusive hadron production in electron-positron annihilation, proton-proton collisions, and deep-inelastic lepton-proton scattering. These analyses complement previous results for pion and kaon fragmentation functions with charge and flavor discrimination. The Lagrange multiplier technique is used to assess the uncertainties in the extraction of the new sets of fragmentation functions.Comment: 14 pages, 14 figure

QCD Hard Scattering and the Sign of the Spin Asymmetry A_LL^pi

Recent preliminary PHENIX data are consistent with a negative and sizable longitudinal double-spin asymmetry A_LL^pi for pi^0 production at moderate transverse momentum p_perp \simeq 1 - 4 GeV and central rapidity. By means of a systematic investigation of the relevant degrees of freedom we show that the perturbative QCD framework at leading power in p_perp produces at best a very small negative asymmetry in this kinematic range.Comment: 4 pages, 3 figures, final version published in PRL (only minor changes; note: title changed in published version