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]