5,025 research outputs found
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
Determination of gluon polarization from deep inelastic scattering and collider data
We investigate impact of -production data at Relativistic Heavy Ion
Collider (RHIC) and future E07-011 experiment for the structure function
of the deuteron at the Thomas Jefferson National Accelerator Facility (JLab) on
studies of nucleonic spin structure, especially on the polarized gluon
distribution function. By global analyses of polarized lepton-nucleon
scattering and the -production data, polarized parton distribution
functions are determined and their uncertainties are estimated by the Hessian
method. Two types of the gluon distribution function are investigated. One is a
positive distribution and the other is a node-type distribution which changes
sign at . Although the RHIC data seem to favor the node
type for , it is difficult to determine a precise functional form
from the current data. However, it is interesting to find that the gluon
distribution is positive at large () due to constraints
from the scaling violation in and RHIC data. The JLab-E07-011
measurements for should be also able to reduce the gluon uncertainty,
and the reduction is comparable to the one by RUN-5 -production data at
RHIC. The reduction is caused by the error correlation between polarized
antiquark and gluon distributions and by a next-to-leading-order (NLO) gluonic
effect in the structure function . We find that the JLab-E07-011 data
are accurate enough to probe the NLO gluonic term in . Both RHIC and JLab
data contribute to better determination of the polarized gluon distribution in
addition to improvement on polarized quark and antiquark distributions.Comment: 11 pages, 9 eps figures, To be published in Nuclear Physics B. AAC08
FORTRAN package is available at the web site http://spin.riken.bnl.gov/aac
Nuclear corrections of parton distribution functions
We report global analysis results of experimental data for nuclear
structure-function ratios F_2^A/F_2^{A'} and proton-nucleus Drell-Yan
cross-section ratios sigma_{DY}^{pA}/sigma_{DY}^{pA'} in order to determine
optimum parton distribution functions (PDFs) in nuclei. An important point of
this analysis is to show uncertainties of the distributions by the Hessian
method. The results indicate that the uncertainties are large for gluon
distributions in the whole x region and for antiquark distributions at x>0.2.
We provide a code for calculating any nuclear PDFs at given x and Q^2 for
general users. They can be used for calculating high-energy nuclear reactions
including neutrino-nucleus interactions, which are discussed at this workshop.Comment: 1+6 pages, LaTeX, 10 eps files, espcrc2.sty, to be published in Nucl.
Phys. B Supplements, Proceedings of the Third International Workshop on
Neutrino-Nucleus Interactions in the Few GeV Region (NuInt04), Gran Sasso,
Italy, March 17-21, 2004. Nuclear PDF library is available at
http://hs.phys.saga-u.ac.jp/nuclp.htm
Global analysis of AAC for determining polarized parton distribution functions
We report global analysis results for polarized parton distribution functions
in the nucleon. The optimum distributions are determined by using spin
asymmetry data on polarized lepton scattering on proton, neutron, and deuteron.
Their uncertainties are estimated by the Hessian method. As a result, polarized
quark distributions are relatively well determined, whereas the polarized gluon
distribution has a large uncertainty band. We find that the obtained gluon
distribution is compatible with recent \Delta g/g measurements in high-p_T
hadron productions.Comment: 3 pages, 2 figures, to be published in the proceedings of the XVIIth
Particles and Nuclei International Conference (PANIC), Santa Fe, New Mexico,
USA, October 24-28, 200
A possible nuclear effect on the NuTeV sin^2 theta_W anomaly
We investigate a possible explanation for the NuTeV anomaly in terms of a
nuclear correction difference between u_v and d_v distributions. Analyzing deep
elastic scattering and Drell-Yan data for nuclear targets, we try to determine
the correction difference and its effect on the anomaly. We find that the
difference cannot be precisely determined at this stage due to the lack of data
which are sensitive to the difference. Therefore, it is difficult to draw a
solid conclusion about its effect although the anomaly could be explained, at
least partially, by this kind of nuclear correction.Comment: 3 pages, 1 figure, to be published in the proceedings of the XVIIth
Particles and Nuclei International Conference (PANIC), Santa Fe, New Mexico,
USA, October 24-28, 200
- …