83 research outputs found
On the relation between nuclear and nucleon Structure Functions and their moments
Calculations of nuclear Structure Functions (SF) F_k^A(x,Q^2) routinely
exploit a generalized convolution, involving the SF for nucleons F_k^N and the
linking SF f^{PN,A} of a fictitious nucleus, composed of point-particles, with
the latter usually expressed in terms of hadronic degrees of freedom. For
finite Q^2 the approach seemed to be lacking a solid justification and the same
is the case for recently proposed, effective nuclear parton distribution
functions (pdf), which exactly reproduce the above-mentioned hadronically
computed F_k^A. Many years ago Jaffe and West proved the above convolution in
the Plane Wave Impulse Approximation (PWIA) for the nuclear components in the
convolution. In the present note we extend the above proof to include classes
of nuclear Final State Interactions (FSI). One and the same function appears to
relate parton distribution functions (pdf) in nuclei and nucleons, and SF for
nuclear targets and for nucleons. That relation is the previously conjectured
one,with an entirely different interpretation of f^{PN,A}. We conclude with an
extensive analysis of moments of nuclear SF based on the generalized
convolution. Characteristics of those moments are shown to be quite similar to
the same for a nucleon. We conclude that the above evidences asymptotic freedom
of a nucleon in a medium and not of a composite nucleus.Comment: 18 pages, 9 figure
Tortuous ways to the extraction of neutron observables from inclusive lepton scattering
We analyze new JLAB data for inclusive electron scattering on various
targets. Computed and measured total inclusive cross sections in the range
show on a logarithmic scale reasonable agreement
for all targets. However, closer inspection of the Quasi-Elastic components
bares serious discrepancies. EMC ratios which may contain less systematic
errors fare the same. The above observations for the new data do not enable the
extraction of the magnetic form factor (FF) and the Structure Function
(SFs) of the neutron, although the application of exactly the same
analysis to older data had been successful. We add to the above analysis older
CLAS collaboration on . Removing some scattered points, it appears
possible to obtain the above mentioned neutron information. We compare our
results with others from alternative sources. Particular attention is paid to
the A=3 iso-doublet. Present data exist only for He, but the available
input and charge symmetry also enable computations for H. Their average is
the computed iso-scalar part and is compared with the empirical modification of
He towards a fictitious A=3 iso-singlet.Comment: 27 pages, 30 figure
The neutron magnetic form factor G_M^n(Q^2) from Quasi-Elastic inclusive scattering data on D and 4He
We analyze cross sections for Quasi-Elastic inclusive scattering of electrons
on nuclei and show that the observed isolated peaks for relatively low
are unique for the lightest targets. Focusing in particular on D and He, we
investigate in two ways to what measure the above peaks can be allocated to
nucleon-elastic processes. We first compute approximate upper limits for the
nucleon-inelastic background in the Quasi-Elastic region due to inclusive
excitation, and find those to be small. Far more precise is a
semi-phenomenological approach, where the dominance of nucleon-elastic
processes is translated into a set of stringent requirements. We show that
those are very well fulfilled for recent D data, and to a somewhat lesser
extent for older D and He data. With knowledge of and
information on , we then extract and find agreement with values
obtained by alternative methods. We discuss the sensitivity of the extraction
method and mention future applications.Comment: 21 pages, 9 figures, revtex4, revised version, Phys. Rev. C, in pres
On Distribution Functions for Partons in Nuclei
We suggest that a previously conjectured relation between Structure Functions
(SF) for nuclei and nucleons also links distribution functions (df) for partons
in a nucleus and in nucleons. The above suggestion ensures in principle
identical results for SF , whether computed with hadronic or partonic
degrees of freedom. In practice there are differences, due to different
input. We show that the thus defined nuclear parton distribution functions
(pdf) respect standard sumrules. In addition we numerically compare some
moments of nuclear SF, and find agreement between results, using hadronic and
partonic descriptions. We present computations of EMC ratios for both, and
compare those with hadronic predictions and data. In spite of substantial
differences in the participating SF, the two representations produce
approximately the same EMC ratios. The apparent correlation between the above
deviations is ascribed to a sumrule for . We conclude with a discussion
of alternative approaches to nuclear pdf.Comment: 14 pages, 4 figure
Nuclear transparencies for nucleons, knocked-out under various semi-inclusive conditions
Using hadron dynamics we calculate nuclear transparencies for protons,
knocked-out in high-, semi-inclusive reactions. Predicted transparencies
are, roughly half a standard deviation above the NE18 data. The latter contain
the effects of binned proton missing momenta and mass, and of finite detector
acceptances. In order to test sensitivity we compare computed transparencies
without restrictions and the same with maximal cuts for missing momenta and the
electron energy loss. We find hardly any variation, enabling a meaningful
comparison with data and predictions based on hadron dynamics. Should
discrepancies persist in high-statistics data, the above may with greater
confidence be attributed to exotic components in the description of the
outgoing proton.Comment: 13 pages + 3 figsin appended PS file, report # WIS-94/43/Oct-P
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