This paper gives the results of a study of single-pion production by the weak charged current utilizing the wide-band muon-type-neutrino beam at the Argonne Zero Gradient Synchrotron. The data were obtained from hydrogen and deuterium fillings of the 12-ft bubble chamber. The methods of event selection and separation from background are given as are the details of the corrections and systematic effects in the data sample. The energy-dependent cross sections and differential distributions are presented for the three single-pion production reactions vp -p p y + , vn +p and vn -p -n r f . An isospin decomposition shows that the ratio of I = , to I = amplitudes is 0.68k0.04 with a relative phase of (90.7k4.6)" for M ( N a ) < 1.4 GeV. This agrees with theoretical models, particularly the detailed calculation of Adler. Using the data of the reaction vp -p-pa+, the characteristic mass of the nucleon axial-vector elastic form factor is measured to be 0.98' ::;GeV when analyzed within the context of the Adler model. The data are also compared to other parametrizations of the nucleon axial-vector form factor. 1161

Next-to-leading-order QCD analyses of the ZEUS data on deep inelastic scattering together with fixed-target data have been performed, from which the gluon and quark densities of the proton and the value of the strong coupling constant ␣ s (M Z ) were extracted. The study includes a full treatment of the experimental systematic uncertainties including point-to-point correlations. The resulting uncertainties in the parton density functions are presented. A combined fit for ␣ s (M Z ) and the gluon and quark densities yields a value for ␣ s (M Z ) in agreement with the world average. The parton density functions derived from ZEUS data alone indicate the importance of HERA data in determining the sea quark and gluon distributions at low x. The limits of applicability of the theoretical formalism have been explored by comparing the fit predictions to ZEUS data at very low Q 2 .

We suggest a method of determination of the pion structure function down to x ≃ 10 −4 based on semi-exclusive deep inelastic scattering off protons.The idea is to exploit the nonperturbative πN and π∆ Fock components of the nucleon, which contribute significantly to deep inelastic scattering and dominate the fragmentation of protons into fast neutrons and deltas. The intrinsic factorization properties of the semi-exclusive cross section give a good test for the validity of this approach.Typeset using REVT E X 1

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