Index
Polarized parton distribution functions are determined by using world data from the longitudinally polarized deep inelastic scattering experiments. A new parametrization of the parton distribution functions is adopted by taking into account the positivity and the counting rule. From the fit to the asymmetry data A_1, the polarized distribution functions of u and d valence quarks, sea quarks, and gluon are obtained. The results indicate that the quark spin content is \Delta\Sigma=0.20 and 0.05 in the leading order (LO) and the next-to-leading-order (NLO) MS-bar scheme, respectively. However, if x dependence of the sea-quark distribution is fixed at small x by "perturbative QCD" and Regge theory, it becomes \Delta \Sigma=0.24 ~ 0.28 in the NLO. The small-x behavior cannot be uniquely determined by the existing data, which indicates the importance of future experiments. From our analysis, we propose one set of LO distributions and two sets of NLO ones as the longitudinally-polarized parton distribution functions.
We discuss possible studies of parton distributions at the proposed 50-GeV PS facility. First, comments are given in general on the importance of large-x physics for finding new physics. Second, polarized deuteron reactions are discussed in connection with new structure functions which are specific for a spin-1 hadron. Third, if the polarized proton-deuteron Drell-Yan process is studied at the facility, it could provide information on the light-antiquark flavor asymmetry in the polarized distributions.
We discuss the possibility of finding polarized antiquark flavor asymmetry in Drell-Yan processes. We find that the difference between polarized proton-proton and proton-deuteron Drell-Yan cross sections should provide valuable information on the polarized flavor asymmetry. Numerical results indicate that the asymmetry effects are conspicuous especially in the large-x_F region. Our analysis is important for the transversity distributions because the flavor asymmetry cannot be found by inclusive lepton scattering and W-production processes.
Polarized parton distribution functions are determined by using asymmetry A_1 data from longitudinally polarized deep inelastic scattering experiments. From our \chi^2 analysis, polarized u-valence, d-valence, antiquark, and gluon distributions are obtained. We propose one set of leading-order distributions and two sets of next-to-leading-order ones as the longitudinally-polarized parton distribution functions.
We discuss the Drell-Yan proton-deuteron (p-d) asymmetry R_{pd}, which is defined by the proton-proton and proton-deuteron cross-section ratio \Delta_{(T)}\sigma^{pd}/2\Delta_{(T)}\sigma^{pp}, and its relation to the polarized light-antiquark flavor asymmetry. Using a formalism of the polarized pd Drell-Yan process, we show that the R_{pd} especially in the large-x_F region is very useful for finding the flavor asymmetry in the longitudinally-polarized and transversity distributions. Our results are particularly important to study the flavor asymmetry in the transversity distributions because they cannot be measured by inclusive deep inelastic scattering and W-production process.
We report the polarized parton distributions proposed by the Asymmetry Analysis Collaboration (AAC). Using parametrized distributions at Q^2=1 GeV^2 and measured A_1 data, we determine optimum polarized distributions in the leading order (LO) and next-to-leading order (NLO). We find that the polarized antiquark distribution is not well determined particularly at small x. It could lead to a rather small quark spin content in comparison with usually-quoted values of 10-30%. In our analysis, it varies from 5% to 28% depending on the small-x extrapolation. It is necessary to have small-x (<10^{-3}) data for precise determination. In addition, the large-x region should be also studied for \Delta q-bar, which cannot be determined solely by g_1. We propose three sets of distributions as the longitudinally polarized parton distribution functions.
Physics of spin-1 hadron is an unexplored topic in the high-energy region although spin-1/2 physics has been well investigated in the last decade. It is important to test our knowledge of hadron spin structure in a quite different field of spin physics. We discuss tensor structure functions, which do not exist for the spin-1/2 nucleon, in lepton scattering and in hadron reactions such as the polarized proton-deuteron Drell-Yan process.
We study parametrization of polarized parton distribution functions in the alpha_s leading order (LO) and in the next-to-leading order (NLO). From \chi^2 fitting to the experimental data on A_1, optimum polarized distribution functions are determined. The quark spin content \Delta\Sigma is very sensitive to the small-x behavior of antiquark distributions which suggests that small-x data are needed for precise determination of \Delta\Sigma. We propose three sets of distributions and also provide FORTRAN library for our distributions.