6,274 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 fragmentation functions and their application to exotic-hadron search
We discuss studies on determination of fragmentation functions and an
application to exotic-hadron search by using characteristic differences between
favored and disfavored functions. The optimum fragmentation functions are
determined for pion, kaon, and proton in the leading order (LO) and
next-to-leading order (NLO) of the running coupling constant alpha_s by global
analyses of hadron-production data in electron-positron annihilation. Various
parametrization results are much different in disfavored-quark and gluon
fragmentation functions; however, we show that they are within uncertainties of
the determined functions by using the Hessian method for uncertainty
estimation. We find that the uncertainties are especially large in the
disfavored-quark and gluon fragmentation functions. NLO improvements are
explicitly shown in the determination by comparing uncertainties of the LO and
NLO functions. Next, we propose to use differences between favored and
disfavored fragmentation functions for determining internal quark
configurations of exotic hadrons. We make a global analysis for f_0 (980) for
finding its internal configuration; however, uncertainties are too large to
specify the structure at this stage.Comment: 8 pages, LaTeX, 7 eps files, Progress of Theoretical Physics,
Supplement in press. Proceedings of New Frontiers in QCD 2010 - Exotic Hadron
Systems and Dense Matter -, Jan.18 - Mar.19, 2010, Kyoto, Japa
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
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]
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
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