Parton distribution functions in nuclei

Optimum nuclear parton distributions are determined by an analysis of muon and electron deep inelastic scattering data. Assuming simple A dependence and polynomial functions of x and 1-x for nuclear modification of parton distributions, we determine the initial distributions by a chi^2 analysis. Although valence-quark distributions are relatively well determined except for the small-x region, antiquark distributions cannot be fixed at medium and large x. It is also difficult to fix gluon distributions.Comment: 1+4 pages, LaTeX2e, ws-p8-50x6-00.cls, 4 eps figures. Talk given at the 9th International Workshop on Deep Inelastic Scattering, Bologna, Italy, April 27 - May 1, 2001. To be published in proceedings. Computer codes for the nuclear parton distributions could be obtained from http://hs.phys.saga-u.ac.jp Email: [email protected], [email protected], [email protected]

Determination of polarized parton distribution functions

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.Comment: 1+5 pages, LATEX, aipproc.sty, 4 eps figures. Talk given at the 14th International Spin Physics Symposium, Osaka, Japan, October 16-21, 200

Transversity distributions and Drell-Yan spin asymmetries

We discuss transversity distributions and Drell-Yan transverse double spin asymmetries. First, the antiquark flavor asymmetry $\Delta_{_T} \bar u/\Delta_{_T} \bar d$ is discussed by using two different descriptions, a meson-cloud model and a Pauli exclusion model. We find that both calculations produce a significant $\Delta_{_T} \bar d$ excess over $\Delta_{_T} \bar u$. Next, we study its effects on the transverse spin asymmetry $A_{_{TT}}$ and on the Drell-Yan proton-deuteron asymmetry $\Delta_{_T}\sigma^{pd}/2 \Delta_{_T}\sigma^{pp}$. We find that the ratio $\Delta_{_T}\sigma^{pd}/2 \Delta_{_T}\sigma^{pp}$ is very useful for investigating the flavor asymmetry effect.Comment: 1+3 pages, LATEX with npb.sty, 2 eps figures. Talk given at the 7th International Workshop on Deep Inelastic Scattering and QCD, DESY Zeuthen, Germany, April 29 -- 23,1999, to be published in Nuclear Physics B. Complete postscript file including the figures is available at http://www2.cc.saga-u.ac.jp/saga-u/riko/physics/quantum1/structure.html Email: [email protected]

Parametrization of nuclear parton distributions

Optimum nuclear parton distributions are obtained by analyzing available experimental data on electron and muon deep inelastic scattering (DIS). The distributions are given at Q^2=1 GeV^2 with a number of parameters, which are determined by a chi^2 analysis of the data. Valence-quark distributions are relatively well determined at medium x, but they are slightly dependent on the assumed parametrization form particularly at small x. Although antiquark distributions are shadowed at small x, their behavior is not obvious at medium x from the F_2 data. The gluon distributions could not be restricted well by the inclusive DIS data; however, the analysis tends to support the gluon shadowing at small x. We provide analytical expressions and computer subroutines for calculating the nuclear parton distributions, so that other researchers could use them for applications to other high-energy nuclear reactions.Comment: 1+11 pages, LaTeX, amsmath.sty, wrapfig.sty, graphicx.sty, ias.cls, ias.sty, pramana.sty, pmana10.sty, pbib.sty, times.sty, 9 eps figures. Invited talk given at the International Symposium on Nuclear Physics, Mumbai, India, Dec. 18-22, 2000, to be published in proceedings. Complete postscript file is available at http://www-hs.phys.saga-u.ac.jp Email: [email protected], [email protected], [email protected]