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 $0.3\lesssim x\lesssim 0.95$ 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) $G_M^n$ and the Structure Function (SFs) $F_2^n$ 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 $F_2^D$. 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 $^3$He, but the available input and charge symmetry also enable computations for $^3$H. Their average is the computed iso-scalar part and is compared with the empirical modification of $^3$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 $Q^2$ are unique for the lightest targets. Focusing in particular on D and $^4$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 $\Delta$ 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 $^4$He data. With knowledge of $G_{E,M}^p$ and information on $G_E^n$, we then extract $G_M^n$ 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 $F_2^A$, whether computed with hadronic or partonic degrees of freedom. In practice there are differences, due to different $F_2^n$ 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 $F_2^A$. 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-$Q^2$, 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