16 research outputs found
Role of Vector Mesons in High-Q^2 Lepton-Nucleon Scattering
The possible role played by vector mesons in inclusive deep inelastic
lepton-nucleon scattering is investigated. In the context of the convolution
model, we calculate self-consistently the scaling contribution to the nucleon
structure function using the formalism of time-ordered perturbation theory in
the infinite momentum frame. Our results indicate potentially significant
effects only when the vector meson---nucleon form factor is very hard.
Agreement with the experimental antiquark distributions, however, requires
relatively soft form factors for the , and vertices.Comment: 22 pages, 9 figures (available upon request); accepted for
publication in Phys.Rev.D, ADP-92-197/T12
Neutron structure function and inclusive DIS from H-3 and He-3 at large Bjorken-x
A detailed study of inclusive deep inelastic scattering (DIS) from mirror A =
3 nuclei at large values of the Bjorken variable x is presented. The main
purpose is to estimate the theoretical uncertainties on the extraction of the
neutron DIS structure function from such nuclear measurements. On one hand,
within models in which no modification of the bound nucleon structure functions
is taken into account, we have investigated the possible uncertainties arising
from: i) charge symmetry breaking terms in the nucleon-nucleon interaction, ii)
finite Q**2 effects neglected in the Bjorken limit, iii) the role of different
prescriptions for the nucleon Spectral Function normalization providing baryon
number conservation, and iv) the differences between the virtual nucleon and
light cone formalisms. Although these effects have been not yet considered in
existing analyses, our conclusion is that all these effects cancel at the level
of ~ 1% for x < 0.75 in overall agreement with previous findings. On the other
hand we have considered several models in which the modification of the bound
nucleon structure functions is accounted for to describe the EMC effect in DIS
scattering from nuclei. It turns out that within these models the cancellation
of nuclear effects is expected to occur only at a level of ~ 3%, leading to an
accuracy of ~ 12 % in the extraction of the neutron to proton structure
function ratio at x ~ 0.7 -0.8$. Another consequence of considering a broad
range of models of the EMC effect is that the previously suggested iteration
procedure does not improve the accuracy of the extraction of the neutron to
proton structure function ratio.Comment: revised version to appear in Phys. Rev. C; main modifications in
Section 4; no change in the conclusion
The Nucleon's Virtual Meson Cloud and Deep Inelastic Lepton Scattering
We address the question whether the nucleon's antiquark sea can be attributed
entirely to its virtual meson cloud and, in essence, whether there exists a
smooth transition between hadronic and quark-gluon degrees of freedom. We take
into account contributions from and mesons and compare with the
nucleon's antiquark distributions which serve as a non-perturbative input to
the QCD evolution equations. We elucidate the different behavior in the flavor
singlet and non-singlet channels and study the dependence of our results on the
scale . The meson-nucleon cut-offs that we determine give not only an
indication on the size of the region within which quarks are confined in a
nucleon, but we find that the scale of these form factors is closely related to
the four-momentum transfer, , where gluons are resolved by a high energy
probe, and that large meson loop momenta, GeV,
contribute significantly to the sea quark distributions. While the agreement of
our calculations with data-based parametrizations is satisfactory and scale
independent for the flavor breaking share of the nucleon's antiquark sea, the
flavor singlet component is quite poorly described. This hints the importance
of gluon degrees of freedom.Comment: 34 pages, RevTeX, 6 figures optionally included using epsfig.st
Soft X ray spectroscopies in liquids and at solid liquid interface at BACH beamline at Elettra
The Beamline for Advanced diCHroism BACH of the Istituto Officina dei Materiali Consiglio Nazionale delle Ricerche IOM CNR , operating at Elettra synchrotron in Trieste Italy , works in the extreme ultra violet EUV soft x ray photon energy range with selectable light polarization, high energy resolution, brilliance and time resolution. The beamline offers a multi technique approach for the investigation of the electronic, chemical, structural, magnetic, and dynamical properties of materials. Recently one of the three end stations has been dedicated to experiments based on electron transfer processes at the solid liquid interfaces and during photocatalytic or electrochemical reactions. Suitable cells to perform soft x ray spectroscopy in the presence of liquids and reagent gases atambient pressure were developed. Here we present two types of static cells working in transmission or in fluorescence yield, and an electrochemical flow cell which allows to carry out cyclic voltammetry in situ, electrodeposition on a working electrode WE and to study chemical reactions in operando conditions. Examples of X ray absorption spectroscopy XAS measurements performed in ambient conditions and during electrochemical experiments in liquids are presente