Parton distributions in the nucleon and nuclei and hadron structure

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(1)Polarized Parton Distribution FunctionsA global analysis has been made for determining the optimum longitudinally-polarized parton distribution functions (PDFs) from spin-asymmetry measurements of polarized lepton-nucleon scattering and pion production in polarized proton-proton collisions. Uncertainties of the polarized PDFs are estimated by the Hessian method. Results indicate that JLab data are useful for determining polarized valence-quark distributions at large x and that HERMES and COMPASS data are valuable for polarized antiquark distributions at around x〜0.1. In addition, PHENIX ones significantly reduce the uncertainty of the polarized gluon distribution.(2)Nuclear Parton Distribution FunctionsWe analyzed experimental data of nuclear structure-function ratios F_2^A/F_2^<A'> and Drell-Yan cross section ratios for obtaining optimum parton distribution functions in nuclei. Higher-order effects are included in this analysis, and new parameters are introduced in order to explain … More mass-number dependence accurately. Then, uncertainties of the nuclear PDFs are estimated by the Hessian method. Valence-quark distributions and antiquark distributions at small x are well determined ; however, the antiquark distributions are not fixed at large x. Gluon distributions have large uncertainties in the whole-x region, so that better future measurements are important. Next, we investigated effects of the difference between u_v and d_v distributions on the NuTeV sin^2θ_W anomaly. We found that such effects can partially explain the anomaly but it may not be large enough. Because such a difference cannot be accurately obtained at this stage, we need future experimental efforts.(3)Fragmentation FunctionsFragmentation functions and their uncertainties are determined by analyzing hadron-production data in electron-positron annihilation. Results indicate that gluon and light-quark fragmentation functions have large uncertainties at small Q^2. Therefore, we should be careful in describing hadron-production reactions in the small p_T region. There are large differences between widely-used functions by KKP (Kniehl, Kramer, and Potter) and Kretzer ; however, they are compatible with each other and also with our functions if the uncertainties are taken into account. Less