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]

Nuclear modification difference between u_v and d_v distributions and its relation to NuTeV sin^2 theta_W anomaly

We investigate a possible nuclear correction to the NuTeV measurement of the weak-mixing angle sin^2 theta_W. In particular, a nuclear modification difference between u_v and d_v distributions contributes to the NuTeV measurement with the iron target. First, the modification differenceis determined by a chi^2 analysis so as to reproduce nuclear data on the structure function F_2 and Drell-Yan processes. Then, taking the NuTeV kinematics into account, we calculate a contribution to the sin^2 theta_W determination. In addition, its uncertainty is estimated by the Hessian method. Although the uncertainty becomes comparable to the NuTeV deviation, the effect is not large enough to explain the whole NuTeV sin^2 theta_W anomaly at this stage. However, it is difficult to determine such a nuclear modification difference, so that we need further investigations on the difference and its effect on the NuTeV anomaly.Comment: 6 pages,3 figure

Nuclear Shadowing in the Structure Function F3(x)F_3(x)

Nuclear modification of the structure function $F_3$ is investigated. Although it could be estimated in the medium and large $x$ regions from the nuclear structure function $F_2^A$, it is essentially unknown at small $x$. The nuclear structure function $F_3^A$ at small $x$ is investigated in two different theoretical models: a parton-recombination model with $Q^2$ rescaling and an aligned-jet model. We find that these models predict completely different behavior at small $x$: {\it antishadowing} in the first parton model and {\it shadowing} in the aligned-jet model. Therefore, studies of the ratio $F_3^A/F_3^D$ at small $x$ could be useful in discriminating among different models, which produce similar shadowing behavior in the structure function $F_2$. We also estimate currently acceptable nuclear modification of $F_3$ at small $x$ by using $F_2^A/F_2^D$ experimental data and baryon-number conservation.Comment: 10 pages, Latex, Figs.1 and 2 are not included, Complete postscript file including the figures is available at ftp://ftp.cc.saga-u.ac.jp/pub/paper/riko/quantum1/saga-he-78.ps.gz or at http://www.cc.saga-u.ac.jp/saga-u/riko/physics/quantum1/structure.htm

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]

Nuclear modification of valence-quark distributions and its effects on NuTeV sin^2 theta_W anomaly

We investigated a nuclear modification difference between up- and down-valence quark distributions by analyzing structure function F_2 and Drell-Yan cross-section ratios. Although nuclear modifications of the valence-quark distributions themselves are rather well determined, it is difficult to find their difference from the present data. We estimated such an effect on the NuTeV sin^2 theta_W value and its uncertainty by the Hessian method. At this stage, it is not large enough to explain the whole NuTeV anomaly. However, the modification difference cannot be precisely determined, so that further studies are needed.Comment: 3 pages, LaTeX, 1 eps file, to be published in Proceedings of the 6th International Workshop on Neutrino Factories and Superbeams (NuFact04

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]