427 research outputs found
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
Electron- and neutrino-nucleus scattering in the impulse approximation regime
A quantitative understanding of the weak nuclear response is a prerequisite
for the analyses of neutrino experiments such as K2K and MiniBOONE, which
measure energy and angle of the muons produced in neutrino-nucleus interactions
in the energy range GeV and reconstruct the incident neutrino energy to
determine neutrino oscillations. In this paper we discuss theoretical
calculations of electron- and neutrino-nucleus scattering, carried out within
the impulse approximation scheme using realistic nuclear spectral
functions.Comparison between electron scattering data and the calculated
inclusive cross section off oxygen, at beam energies ranging between 700 and
1200 MeV, show that the Fermi gas model, widely used in the analysis of
neutrino oscillation experiments,fails to provide a satisfactory description of
the measured cross sections,and inclusion of nuclear dynamics is needed.Comment: 12 pages, 15 figure
Alpha clustering and weak coupling in the A=90 region
From the viewpoint of a unified description of cluster structure and
scattering in the
A=90 region, scattering from Y is investigated.
clustering and weak coupling in Nb is discussed.Comment: 8 pages, 4 figure
Deformed Base Antisymmetrized Molecular Dynamics and its Application to ^{20}Ne
A new theoretical framework named as deformed base antisymmetrized molecular
dynamics that uses the localized triaxially deformed Gaussian as the single
particle wave packet is presented. The model space enables us to describe
sufficiently well the deformed mean-field structure as well as the cluster
structure and their mixed structure within the same framework. The improvement
over the original version of the antisymmetrized molecular dynamics which uses
the spherical Gaussian is verified by the application to
nucleus. The almost pure cluster structure of the
= band, the distortion of the cluster structure in the
= band and the dominance of the deformed mean-field structure of
the = band are confirmed and their observed properties are
reproduced. Especially, the intra-band E2 transition probabilities in
= and bands are reproduced without any effective charge.
Since it has been long known that the pure
cluster model underestimates the intra-band transitions in the
= band by about 30%, we consider that this success is due to the
sufficient description of the deformed mean-field structure in addition to the
cluster structure by the present framework. From the successful description of
, we expect that the present framework presents us with a
powerful approach for the study of the coexistence and interplay of the
mean-field structure and the cluster structure
Quenching of Weak Interactions in Nucleon Matter
We have calculated the one-body Fermi and Gamow-Teller charge-current, and
vector and axial-vector neutral-current nuclear matrix elements in nucleon
matter at densities of 0.08, 0.16 and 0.24 fm and proton fractions
ranging from 0.2 to 0.5. The correlated states for nucleon matter are obtained
by operating on Fermi-gas states by a symmetrized product of pair correlation
operators determined from variational calculations with the Argonne v18 and
Urbana IX two- and three-nucleon interactions. The squares of the charge
current matrix elements are found to be quenched by 20 to 25 % by the
short-range correlations in nucleon matter. Most of the quenching is due to
spin-isospin correlations induced by the pion exchange interactions which
change the isospins and spins of the nucleons. A large part of it can be
related to the probability for a spin up proton quasi-particle to be a bare
spin up/down proton/neutron. We also calculate the matrix elements of the
nuclear Hamiltonian in the same correlated basis. These provide relatively mild
effective interactions which give the variational energies in the Hartree-Fock
approximation. The calculated two-nucleon effective interaction describes the
spin-isospin susceptibilities of nuclear and neutron matter fairly accurately.
However 3-body terms are necessary to reproduce the compressibility. All
presented results use the simple 2-body cluster approximation to calculate the
correlated basis matrix elements.Comment: submitted to PR
-particle condensate states in O
The existence of a rotational band with the +C()
cluster structure, in which three particles in C() are
locally condensed, is demonstrated near the four- threshold of O
in agreement with experiment. This is achieved by studying structure and
scattering for the +C() system in a unified way. A
drastic reduction (quenching) of the moment of the inertia of the state
at 15.1 MeV just above the four- threshold in O suggests that it
could be a candidate for the superfluid state in -particle
condensation.Comment: 5 pages, 3 figure
Measurement of tau polarization in e+ e- annihilation at sqrt{s}=58 GeV
The polarization of tau leptons in the reaction e+ e- --> tau+ tau- has been
measured using a e+e- collider, TRISTAN, at the center-of-mass energy of 58
GeV. From the kinematical distributions of daughter particles in tau --> e nu
nu-bar, mu nu nu-bar, rho nu or pi(K) nu decays, the average polarization of
tau- and its forward-backward asymmetry have been evaluated to be 0.012 +-
0.058 and 0.029 +- 0.057, respectively.Comment: 18 pages, 5 figure
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