223 research outputs found
Final state interaction in inclusive and exclusive quasi-elastic processes
We discuss a new approach to final state interactions, that keeps explicitly
into account the virtuality of the ejected nucleon in quasi-elastic
scattering at very large , and we present some recent results, at
moderately large values, for the nuclear transparency in ,
and and for the momentum distributions of .Comment: 10 pages, 5 figures, Prepared for the workshop "Cortona 2000, VIII
Convegno su Problemi di Fisica Nucleare Teorica
On the effects of the final state interaction in the electro-disintegration of the deuteron at intermediate and high energies
The role of the final state interactions (FSI) in the inclusive quasi-elastic
disintegration of the deuteron is investigated treating the two-nucleon final
state within the exact continuum solutions of the non-relativistic Schroedinger
equation, as well as within the Glauber multiple scattering approach. It is
shown that for values of the Bjorken scaling variable both
approaches provide similar results, unless the case , where
they appreciably disagree. It is demonstrated that present experimental data,
which are mostly limited to a region of four-momentum transfer () where the Center-of-Mass energy of the final state is below the
pion threshold production, can be satisfactorily reproduced by the approach
based on the exact solution of the Schroedinger equation and not by the Glauber
approach. It is also pointed out that the latter, unlike the former, does not
satisfy the inelastic Coulomb sum rule, the violation being of the order of
about 20%.Comment: 16 LaTeX pages, 10 eps-figures, 1 tabl
Ground-state correlations and final state interactions in the process 3He(e,e'pp)n
The two-proton emission process is theoretically investigated
using realistic three-nucleon wave functions and taking the final state
interaction into account by an approach which can be used when the value of the
three-nucleon invariant mass is either below or above the pion emission
threshold. Various kinematical conditions which enhance or minimize the effects
of the final state interaction are thoroughly analyzed.Comment: 26 pages, 12 eps-figures. Introduction and abstract updated, few
references added and Apendix A remove
Nuclear effects in Deep Inelastic Scattering of polarized electrons off polarized 3He and the neutron spin structure functions
It is shown that the nuclear effects playing a relevant role in Deep
Inelastic Scattering of polarized electrons by polarized He are mainly
those arising from the effective proton and neutron polarizations generated by
the and waves in He. A simple and reliable equation relating the
neutron, , and He, , spin structure functions is proposed. It
is shown that the measurement of the first moment of the He structure
function can provide a significant check of the Bjorken Sum Rule.Comment: 11 pages (revTeX), DFUPG 75/93; 5 (postscript) figures available upon
request from the author
Selected Topics in High Energy Semi-Exclusive Electro-Nuclear Reactions
We review the present status of the theory of high energy reactions with
semi-exclusive nucleon electro-production from nuclear targets. We demonstrate
how the increase of transferred energies in these reactions opens a complete
new window in studying the microscopic nuclear structure at small distances.
The simplifications in theoretical descriptions associated with the increase of
the energies are discussed. The theoretical framework for calculation of high
energy nuclear reactions based on the effective Feynman diagram rules is
described in details. The result of this approach is the generalized eikonal
approximation (GEA), which is reduced to Glauber approximation when nucleon
recoil is neglected. The method of GEA is demonstrated in the calculation of
high energy electro-disintegration of the deuteron and A=3 targets.
Subsequently we generalize the obtained formulae for A>3 nuclei. The relation
of GEA to the Glauber theory is analyzed. Then based on the GEA framework we
discuss some of the phenomena which can be studied in exclusive reactions,
these are: nuclear transparency and short-range correlations in nuclei. We
illustrate how light-cone dynamics of high-energy scattering emerge naturally
in high energy electro-nuclear reactions.Comment: LaTex file with 51 pages and 23 eps figure
Strategies to control antibiotic resistance: Results from a survey in Italian children's hospitals
Structure functions for the three nucleon system
The spectral functions and light-cone momentum distributions of protons and
neutrons in 3He and 3H are given in terms of the three-nucleon wave function
for realistic nucleon-nucleon interactions. To reduce computational complexity,
separable expansions are employed for the nucleon-nucleon potentials. The
results for the light-cone momentum distributions suggest that they are not
very sensitive to the details of the two-body interaction, as long as it has
reasonable short-range repulsion. The unpolarised and polarised structure
functions are examined for both 3He and 3H in order to test the usefulness of
3He as a neutron target. It is found that the measurement of the spin structure
function of polarised 3H would provide a very clear test of the predicted
change in the polarised parton distributions of a bound proton.Comment: 30 pages, REVTeX, 11 figure
Relativistic Structure of the Deuteron: 1.Electro-disintegration and y-scaling
Realistic solutions of the spinor-spinor Bethe-Salpeter equation for the
deuteron with realistic interaction kernel including the exchange of pi, sigma,
omega, rho, eta and delta mesons, are used to systematically investigate
relativistic effects in inclusive quasi-elastic electron-deuteron scattering
within the relativistic impulse approximation. Relativistic y-scaling is
considered by generalising the non relativistic scaling function to the
relativistic case, and it is shown that y-scaling does occur in the usual
relativistic scaling variable resulting from the energy conservation in the
instant form of dynamics. The present approach of y-scaling is fully covariant,
with the deuteron being described by eight components, viz. the 3S_1^{++},
3S_1^{--}, 3D_1^{++}, 3D_1^{--}, 3P_1^{+-}, 3P_1^{-+}, 1P_1^{+-}, 1P_1^{-+}
waves. It is demonstrated that if the negative relative energy states 1P_1,
3P_1 are disregarded, the concept of covariant momentum distributions N(p_0,p),
with p_0=M_D/2-\sqrt{p^2+m^2}, can be introduced, and that calculations of
lectro-disintegration cross section in terms of these distributions agree
within few percents with the exact calculations which include the 1P_1, 3P_1
states, provided the nucleon three momentum |p|\<= 1 GeV/c; in this momentum
range, the asymptotic relativistic scaling function is shown to coincide with
the longitudinal covariant momentum distribution.Comment: 32 LaTeX pages, 18 eps-figures. Final version to appear in Phys. Rev.
Extraction of electromagnetic neutron form factors through inclusive and exclusive polarized electron scattering on polarized 3He target
Inclusive 3He(e,e') and exclusive 3He(e,e'n) processes with polarized
electrons and 3He have been theoretically analyzed and values for the magnetic
and electric neutron form factors have been extracted. In both cases the form
factor values agree well with the ones extracted from processes on the
deuteron. Our results are based on Faddeev solutions, modern NN forces and
partially on the incorporation of mesonic exchange currents.Comment: 28 pages, 29 Postscript figure
Feynman Graphs and Generalized Eikonal Approach to High Energy Knock-Out Processes
The cross section of hard semi-exclusive reactions for fixed
missing energy and momentum is calculated within the eikonal approximation.
Relativistic dynamics and kinematics of high energy processes are unambiguously
accounted for by using the analysis of appropriate Feynman diagrams. A
significant dependence of the final state interactions on the missing energy is
found, which is important for interpretation of forthcoming color transparency
experiments. A new, more stringent kinematic restriction on the region where
the contribution of short-range nucleon correlations is enhanced in
semi-exclusive knock-out processes is derived. It is also demonstrated that the
use of light-cone variables leads to a considerable simplification of the
description of high-energy knock-out reactions.Comment: 24 pages, LaTex, two Latex and two ps figures, uses FEYNMAN.tex and
psfig.sty. Revisied version to appear in Phys. Rev.
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