471 research outputs found
Tensor-polarized quark and antiquark distribution functions in a spin-one hadron
To understand orbital-angular-momentum contributions is becoming crucial for
clarifying nucleon-spin issue in the parton level. Twist-two structure
functions b_1 and b_2 for spin-one hadrons could probe orbital-angular-momentum
effects, which reflect a different aspect from current studies for the spin-1/2
nucleon, since they should vanish if internal constituents are in the S state.
These structure functions are related to tensor structure in spin-one hadrons.
Studies of such tensor structure will open a new field of high-energy spin
physics. The structure functions b_1 and b_2 are described by tensor-polarized
quark and antiquark distributions delta_T-q and delta_T-qbar. Using HERMES data
on the b_1 structure function for the deuteron, we made an analysis of
extracting the distributions delta_T-q and delta_T-qbar in a simple x-dependent
functional form. Optimum distributions are proposed for the tensor-polarized
valence and antiquark distribution functions from the analysis. A finite tensor
polarization is obtained for antiquarks if we impose a constraint that the
first moments of tensor-polarized valence-quark distributions vanish. It is
interesting to investigate a physics mechanism to create a finite
tensor-polarized antiquark distribution.Comment: 4 pages, LaTeX, 2 eps figures, Phys. Rev. D in pres
Plans for Hadronic Structure Studies at J-PARC
Hadron-physics projects at J-PARC are explained. The J-PARC is the
most-intense hadron-beam facility in the multi-GeV high-energy region. By using
secondary beams of kaons, pions, and others as well as the primary-beam proton,
various hadron projects are planned. First, some of approved experiments are
introduced on strangeness hadron physics and hadron-mass modifications in
nuclear medium. Second, future possibilities are discussed on hadron-structure
physics, including structure functions of hadrons, spin physics, and
high-energy hadron reactions in nuclear medium. The second part is discussed in
more details because this is an article in the hadron-structure session.Comment: 10 pages, LaTeX, 20 eps files, to be published in Journal of Physics:
Conference Series (JPCS), Proceedings of the 24th International Nuclear
Physics Conference (INPC 2010), Vancouver, Canada, July 4 - 9, 201
Determination of nuclear parton distributions
Parametrization of nuclear parton distributions is investigated in the
leading order of alpha_s. The parton distributions are provided at Q^2=1 GeV^2
with a number of parameters, which are determined by a chi^2 analysis of the
data on nuclear structure functions. Quadratic or cubic functional form is
assumed for the initial distributions. Although valence quark distributions in
the medium x region are relatively well determined, the small x distributions
depend slightly on the assumed functional form. It is difficult to determine
the antiquark distributions at medium x and gluon distributions. From the
analysis, we propose parton distributions at Q^2=1 GeV^2 for nuclei from
deuteron to heavy ones with the mass number A~208. They are provided either
analytical expressions or computer subroutines for practical usage. Our studies
should be important for understanding the physics mechanism of the nuclear
modification and also for applications to heavy-ion reactions. This kind of
nuclear parametrization should also affect existing parametrization studies in
the nucleon because "nuclear" data are partially used for obtaining the optimum
distributions in the "nucleon".Comment: 16 pages, REVTeX4b5, revtex4.cls, url.sty, natbib.sty, 10pt.rtx,
aps.rtx, revsymb.sty, 21 eps figures. Submitted for publication. Computer
codes for the nuclear parton distributions could be obtained from
http://www-hs.phys.saga-u.ac.jp Email: [email protected]
Determination of polarized parton distribution functions with recent data on polarization asymmetries
Global analysis has been performed within the next-to-leading order in
Quantum Chromodynamics (QCD) to determine polarized parton distributions with
new experimental data in spin asymmetries. The new data set includes JLab,
HERMES, and COMPASS measurements on spin asymmetry A_1 for the neutron and
deuteron in lepton scattering. Our new analysis also utilizes the double-spin
asymmetry for pi^0 production in polarized pp collisions, A_{LL}^{pi^0},
measured by the PHENIX collaboration. Because of these new data, uncertainties
of the polarized PDFs are reduced. In particular, the JLab, HERMES, and COMPASS
measurements are valuable for determining Delta d_v(x) at large x and Delta
qbar(x) at x~0.1. The PHENIX pi^0 data significantly reduce the uncertainty of
Delta g(x). Furthermore, we discuss a possible constraint on Delta g(x) at
large x by using the HERMES data on g_1^d in comparison with the COMPASS ones
at x~0.05.Comment: 11 pages, REVTeX, 13 eps files, Phys. Rev. D in pres
A Matrix Approach to Numerical Solution of the DGLAP Evolution Equations
A matrix-based approach to numerical integration of the DGLAP evolution
equations is presented. The method arises naturally on discretisation of the
Bjorken x variable, a necessary procedure for numerical integration. Owing to
peculiar properties of the matrices involved, the resulting equations take on a
particularly simple form and may be solved in closed analytical form in the
variable t=ln(alpha_0/alpha). Such an approach affords parametrisation via data
x bins, rather than fixed functional forms. Thus, with the aid of the full
correlation matrix, appraisal of the behaviour in different x regions is
rendered more transparent and free of pollution from unphysical
cross-correlations inherent to functional parametrisations. Computationally,
the entire programme results in greater speed and stability; the matrix
representation developed is extremely compact. Moreover, since the parameter
dependence is linear, fitting is very stable and may be performed analytically
in a single pass over the data values.Comment: 13 pages, no figures, typeset with revtex4 and uses packages:
acromake, amssym
Nuclear parton distribution functions and their uncertainties
We analyze experimental data of nuclear structure-function ratios
F_2^A/F_2^{A'} and Drell-Yan cross section ratios for obtaining optimum parton
distribution functions (PDFs) in nuclei. Then, uncertainties of the nuclear
PDFs are estimated by the Hessian method. Valence-quark distributions are
determined by the F_2 data at large x; however, the small-x part is not obvious
from the data. On the other hand, the antiquark distributions are determined
well at x~0.01 from the F_2 data and at x~0.1 by the Drell-Yan data; however,
the large-x behavior is not clear. Gluon distributions cannot be fixed by the
present data and they have large uncertainties in the whole x region.
Parametrization results are shown in comparison with the data. We provide a
useful code for calculating nuclear PDFs at given x and Q^2.Comment: 9 pages, REVTeX, 23 eps files, Phys. Rev. C in press. Nuclear PDF
library is available at http://hs.phys.saga-u.ac.jp/nuclp.htm
Nuclear Shadowing in a Parton Recombination Model
Deep inelastic structure functions are investigated in a
rescaling model with parton recombination effects. We find that the model can
explain experimentally measured structure functions reasonably well
in the wide Bjorken range (). In the very small region
(), recombination results are very sensitive to input sea-quark and
gluon distributions.Comment: preprint MKPH-T-93-04, IU/NTC 92-20, 25 pages, TEX file (without
Figs. 1-14)., (address after April 1: Saga U., Japan
Modified Paschos-Wolfenstein relation and extraction of weak mixing angle sin^2 theta_W
The NuTeV collaboration reported anomalously large weak mixing angle sin^2
theta_W in comparison with the standard model prediction. Neutrino and
antineutrino charged- and neutral-current events are analyzed for extracting
sin^2 theta_W. Although the Paschos-Wolfenstein relation is not directly used
in the analysis, it plays an important role in the determination. Noting that
the target nucleus, iron, is not an isoscalar nucleus, we derive a
leading-order expression for a modified Paschos-Wolfenstein relation for
nuclei, which may have neutron excess. Then, using charge and baryon-number
conservations for nuclei, we discuss a nuclear correction in the sin^2 theta_W
determination. It is noteworthy that nuclear modifications are different
between valence up- and down-quark distributions. We show this difference
effect on the NuTeV sin^2 theta_W deviation.Comment: 5 pages, REVTeX4.0, revtex4.cls, url.sty, natbib.sty, revsymb.sty,
10pt.rtx, aps.rtx, amssymb.sty, amsfonts.sty, 3 eps figures. Phys. Rev. D in
press. Email: [email protected] See also http://hs.phys.saga-u.ac.j
Order perturbative QCD corrections to the Gottfried sum rule
The order perturbative QCD correction to the Gottfried sum rule
is obtained. The result is based on numerical calculation of the order
contribution to the coefficient function and on the new estimate
of the three-loop anomalous dimension term. The correction found is negative
and rather small. Therefore it does not affect the necessity to introduce
flavour-asymmetry between and antiquarks for the
description of NMC result for the Gottfried sum rule.Comment: LaTeX, 7 pages, the discussions of the corrections to
the anomalous dimension are modified; 1 reference added; to be published in
Phys. Lett.
Clustering aspects in nuclear structure functions
For understanding an anomalous nuclear effect experimentally observed for the
beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility
(JLab), clustering aspects are studied in structure functions of deep inelastic
lepton-nucleus scattering by using momentum distributions calculated in
antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple
shell model for comparison. According to the AMD, the Be-9 nucleus consists of
two alpha-like clusters with a surrounding neutron. The clustering produces
high-momentum components in nuclear wave functions, which affects nuclear
modifications of the structure functions. We investigated whether clustering
features could appear in the structure function F_2 of Be-9 along with studies
for other light nuclei. We found that nuclear modifications of F_2 are similar
in both AMD and shell models within our simple convolution description although
there are slight differences in Be-9. It indicates that the anomalous Be-9
result should be explained by a different mechanism from the nuclear binding
and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by
the maximum local densities, the Be-9 anomaly can be explained by the AMD
picture, namely by the clustering structure, whereas it certainly cannot be
described in the simple shell model. This fact suggests that the large nuclear
modification in Be-9 should be explained by large densities in the clusters.
For example, internal nucleon structure could be modified in the high-density
clusters. The clustering aspect of nuclear structure functions is an unexplored
topic which is interesting for future investigations.Comment: 11 pages, LaTeX, 10 eps files, Physical Review C in pres
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