The reactionsΣvp→π+n,K+Λ,K+∑0 andΣvn→π+n were studied at invariant hadronic masses around 2.2. GeV forQ2=0.06, 0.28, 0.70, and 1.35 GeV2. The main results are: At small |t| the π+ production is dominated by longitudinally polarized photons and can be described by one pion exchange. At low |t| the transverse (π+n) cross section drops steeply withQ2, but remains roughly constant forQ2≧0.5 GeV2. For |t⊢≧0.8 GeV2, (π+n/dt) is almost independent ofQ2. The integrated cross section (π+n) shows a similarQ2-dependence asσtot (γvp) forQ2≧0.28 GeV2. The ratioσ(π-p)/σ(π+n) atQ2=0.70 and 1.35 GeV2 for |t|≧0.6 GeV2 is smaller than in photoproduction and close to 1/4. The ratioσ(K+∑0 decreases steeply withQ2 following roughly the predictions of the quark-parton model.
PHI AND EPSILON DEPENDENCE FITTED TO GIVE COMPONENTS OF CROSS SECTION.
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We report on an experiment where the different contributions from the transverse and longitudinal polarization of the virtual photon are measured separately for the reaction e − p→e − π + n. The data taken above the resonance region at small ∣ t ∣ values in the q 2 range of ∣ q 2 ∣ < 0.5 GeV 2 show a clear dominance of the longitudinal part of the cross section and are well described by a generalized Born-term model. Using this model the electromagnetic form factor of the pion is determined. At q 2 = −0.35 GeV 2 one gets F π = 0.598 ± 0.021.
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AVERAGED OVER RESTRICTED PHI RANGE. THIS IS MAINLY (D(SIG(NAME=U))/DT + EPS*D(SIG(NAME=L))/DT) SINCE COMPONENTS P AND I ARE EXPECTED TO REMAIN SMALL FOR LARGER -T.
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The four cross section components σ U , σ L , σ P and σ I were separated in the reaction γ V + p → π + + n at an electron four momentum transfer of Q 2 = 0.70 GeV 2 and an invariant hadronic mass of 2.19 GeV in the range of t between t min and −0.28 GeV 2 . The longitudinal cross section σ L dominates at small |t| and decreases rapidly with increasing |t|. The data are in rough agreement with the prediction of a generalized Born term model. The resulting value for the pion electromagnetic form factor is F π = 0.42 ± 0.015.
TMIN = 0.024 GEV**2.
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The reaction e + p → e' + n + π + was studied detecting e' and e' and π + in coincidence at an invariant hadronic mass of 2.19 GeV. The measurements were performed at electron four-momentum transfers squared of Q 2 = 0.06, 0.28, 0.70, and 1.35 GeV 2 in the range of t = ( γ v − π ) 2 between t min and −1.0 GeV 2 . The cross section d 2 σ / dtd was found to be roughly independent of Q 2 for Q 2 > 0.7 GeV 2 and ∥ t ∥ > 0.2 GeV 2 .
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