660 research outputs found
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]
Proposal for exotic-hadron search by fragmentation functions
It is proposed that fragmentation functions should be used to identify exotic
hadrons. As an example, fragmentation functions of the scalar meson f_0(980)
are investigated. It is pointed out that the second moments and functional
forms of the u- and s-quark fragmentation functions can distinguish the
tetraquark structure from . By the global analysis of f_0 (980)
production data in electron-positron annihilation, its fragmentation functions
and their uncertainties are determined. It is found that the current available
data are not sufficient to determine its internal structure, while precise data
in future should be able to identify exotic quark configurations.Comment: 4 pages, 4 figures, revtex, To be published in PR
Determination of nuclear parton distribution functions and their uncertainties at next-to-leading order
Nuclear parton distribution functions (NPDFs) are determined by global
analyses of experimental data on structure-function ratios F_2^A/F_2^{A'} and
Drell-Yan cross-section ratios \sigma_{DY}^A/\sigma_{DY}^{A'}. The analyses are
done in the leading order (LO) and next-to-leading order (NLO) of running
coupling constant \alpha_s. Uncertainties of the NPDFs are estimated in both LO
and NLO for finding possible NLO improvement. Valence-quark distributions are
well determined, and antiquark distributions are also determined at x<0.1.
However, the antiquark distributions have large uncertainties at x>0.2. Gluon
modifications cannot be fixed at this stage. Although the advantage of the NLO
analysis, in comparison with the LO one, is generally the sensitivity to the
gluon distributions, gluon uncertainties are almost the same in the LO and NLO.
It is because current scaling-violation data are not accurate enough to
determine precise nuclear gluon distributions. Modifications of the PDFs in the
deuteron are also discussed by including data on the proton-deuteron ratio
F_2^D/F_2^p in the analysis. A code is provided for calculating the NPDFs and
their uncertainties at given x and Q^2 in the LO and NLO.Comment: 15 pages, LaTeX, 22 eps files, to appear in PRC. A code for
calculating our nuclear parton distribution functions and their uncertainties
can be obtained from http://research.kek.jp/people/kumanos/nuclp.htm
Determination of fragmentation functions and their uncertainties from e+ + e- -> h + X data
Fragmentation functions are determined for pions, kaons, and nucleons by a
global analysis of charged-hadron production data in electron-positron
annihilation. The optimum functions are obtained in both leading order (LO) and
next-to-leading order (NLO) of alpha_s. It is important that uncertainties of
the fragmentation functions are estimated in this work by the Hessian method.
We found that the uncertainties are large at small Q^2 and that they are
generally reduced in the NLO in comparison with the LO ones. We supply a code
for calculating the fragmentation functions and their uncertainties for the
pions, kaons, and nucleons at given z and Q^2.Comment: 4 pages, LaTeX, 5 eps files, to be published in AIP proceedings of
the 17th International Spin Physics Symposium (SPIN2006), Oct. 2-7, 2006,
Kyoto, Japa
Selected topics on parton distribution functions
We report recent studies on structure functions of the nucleon and nuclei.
First, clustering effects are investigated in the structure function F_2 of
Be-9 for explaining an unusual nuclear correction found in a JLab experiment.
We propose that high densities created by formation of clustering structure
like 2*alpha+neutron in Be-9 is the origin of the unexpected JLab result by
using the antisymmetrized molecular dynamics (AMD). There is an approved
proposal at JLab to investigate the structure functions of light nuclei
including the cluster structure, so that much details will become clear in a
few years. Second, tensor-polarized quark and antiquark distributions are
obtained by analyzing HERMES measurements on the structure function b_1 for the
deuteron. The result suggests a finite tensor polarization for antiquark
distributions, which is an interesting topic for further theoretical and
experimental investigations. An experimental proposal exists at JLab for
measuring b_1 of the deuteron as a new tensor-structure study in 2010's.
Furthermore, the antiquark tensor polarization could be measured by polarized
deuteron Drell-Yan processes at hadron facilities such as J-PARC and GSI-FAIR.
Third, the recent CDF dijet anomaly is investigated within the standard model
by considering possible modifications of the strange-quark distribution. We
find that the shape of a dijet-mass spectrum changes depending on the
strange-quark distribution. It indicates that the CDF excess could be partially
explained as a PDF effect, particularly by the strangeness in the nucleon,
within the standard model if the excess at m_{jj}~140 GeV is not a sharp peak.Comment: 8 pages, LaTeX, to be published in AIP proceedings, 8th
Circum-Pan-Pacific Symposium on High Energy Spin Physics, June 20-24, 2011,
Cairns, Australi
Determination of f_0(980) Structure by Fragmentation Functions
We discuss internal structure of an exotic hadron by using fragmentation
functions. The fragmentation functions for the f_0(980) meson are obtained by a
global analysis of e^++e^- \to f_0+X data. Quark configuration of the f_0(980)
could be determined by peak positions and second moments of the obtained
fragmentation functions.Comment: 4page, 2eps figures, To appear in the proceedings of Chiral Symmetry
in Hadron and Nuclear Physics (Chiral 07), Osaka, Japan, 13-16 Nov. 200
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