We report recent work on the extraction of R = σL/σT and the structure function F2 over a large kinematic range. which is based on a reanalysis of deep ine!astjc ϵ - p and ϵ - d scattering cross ...sections measured at SLAC between 1970 and 1985. All these data were corrected for radiative effects using improved versions of external and internal radiative correction procedures. The data from seven individual experiments were normalized to those from the recent high-precision SLAC experiment E140. We find that Rp = Rd. as expected in QCD. The value of R is higher than predicted by QCD even when target-mass effects are included, This difference indicates that additional dynamical higher-twist effects may be present. The structure functions F2p and F2d were also extracted from the full data sets of normalized cross sections using an empirical fit to R. These structure functions were then compared with data from the CERN muon scattering experiments BCDIMS and EMC. We find that our data are consistent with the EMC data, if the latter are multiplied by a normalization factor of 1.07. No single, uniform normalization factor can be applied to the BCDMS data that will bring them into agreement with the SLAC data in the region of overlap.
The H(e,e'pi+)n cross section was measured at four-momentum transfers of Q2=1.60 and 2.45 GeV2 at an invariant mass of the photon nucleon system of W=2.22 GeV. The charged pion form factor (F_pi) was ...extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F_pi is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q2 by one sigma, but is still far from its perturbative Quantum Chromo-Dynamics prediction.
We report measurements of the proton form factors ital Gsub ital Esup ital p and ital Gsub ital Msup ital p extracted from elastic scattering in the range 1leital Qsup 2le3 (GeV/ital c)sup 2 with ...total uncertainties lt 15% in ital Gsub ital Esup ital p and lt 3% in ital Gsub ital Msup ital p. Comparisons are made to theoretical models, including those based on perturbative QCD, vector-meson dominance, QCD sum rules, and diquark constituents in the proton. The results for ital Gsub ital Esup ital p are somewhat larger than indicated by most theoretical parametrizations, and the ratios of the Pauli and Dirac form factors ital Qsup 2(ital Fsub 2sup ital p/ital Fsub 1sup ital p) are lower in value and demonstrate a weaker ital Qsup 2 dependence than those predictions. A global extraction of the elastic form factors from several experiments in the range 0.1 lt ital Qsup 2 lt 10 (GeV/ital c)sup 2 is also presented.
We report results on a precision measurement of the ratio ital R=sigmasub ital L/sigmasub ital T in deep inelastic electron-nucleon scattering in the kinematic range 0.2leital xle0.5 and 1leital Qsup ...2le10 (GeV/ital c)sup 2. Our results show, for the first time, a clear falloff of ital R with increasing ital Qsup 2. Our ital R results are in agreement with QCD predictions only when corrections for target mass effects and some additional higher twist effects are included. At small ital x, the data on ital R favor structure functions with a large gluon contribution. We also report results on the differences ital Rsub ital Aminusital Rsub ital D and the cross section ratio sigmasup ital A/sigmasup ital D between Fe and Au nuclei and the deuteron. Our results for ital Rsub ital Aminusital Rsub ital D are consistent with zero for all ital x,ital Qsup 2 indicating that possible contributions to ital R from nuclear higher twist effects and spin-0 constituents in nuclei are not different from those in nucleons. The ratios sigmasup ital A/sigmasup ital D from all recent experiments, at all ital x,ital Qsup 2 values, are now in agreement.
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