E. Rabe

RHO PRODUCTION BY VIRTUAL PHOTONS

The reaction 3,vp -+ pcr+Tr - was studied in the W, Q2 region 1.3-2.8 GeV, 0.3-1.4 GeV 2 using tile streamer chamber at DESY. A detailed analysis of rho production via ~,vp ~ p 0p is presented. Near threshold rho production has peripheral and non-peripheral contributions of comparable magnitude. At higher energies (14/> 2 GeV) the peripheral component is dominant. The Q2 dependence of o(q, vp ~ o 0p) follows that of the rho propagator as predicted by VDM. The slope of do/dt at ~ Qz ) = 0.4 and 0.8 GeV 2 is within errors equal to its value at Q2 = 0. The overall shape of thep ° is t dependent as in photoproduction, but is independent of Q2. The decay angular distribution shows that longitudinal rhos dominate in the threshold region. At higher energies transverse rhos are dominant. Rho prod)~ction by transverse photons proceeds almost exclusively by natural parity exchange, o T ~ (0.83 -+ 0.06) e T for 2.2 2 GeV.

Study of photoproduction on hydrogen in a streamer chamber with tagged photons for 1.6 GeV

We have studied photoproduction using a 1 m streamer chamber at DESY and a tagged photon beam with an energy range of 1.6 GeV < Eγ < 6.3 GeV. We analysed approximately 30 000 events and report topological, channel and resonance production cross sections for a large number of reactions with three and five outgoing charged particles.

< E_\gamma <

Electroproduction in the kinematical region 0.3 < Q2 < 1.5 GeV2, mp ⩽ W < 2.8 GeV has been studied with a streamer chamber at DESY. The average multiplicity of charged hadrons is found to be somewhat smaller (∼ 10%) than for photoproduction. The normalized π− inclusive momentum spectra show less leading negative pions with increasing Q2. The reaction ep → epπ+π− has been analyzed. The mass distributions show strong Δ++ formation at low energies and dominant π0 production for high energies. The cross sections for Δ++ and ϱ0 production have been determined by maximum-likelihood fits. The ratio of ϱ0 to total inelastic production drops with Q2 from (16.6 ± 0.8)% at Q2 = 0 to (7.6 ± 2.1)% [(4.3 ± 2.9)%] at 〈Q2〉 = 0.6 [1.04] GeV2. The t-distribution for events in the ϱ mass region becomes increasingly flat with Q2. The ϱ0 decay angular distribution has been analyzed in the helicity system. Near threshold (1.7 < W < 2 GeV) the ϱ0 mesons are longitudinally polarized. For higher energies more transversely-aligned ϱ0 mesons are being produced. Under the assumption of s-channel helicity conservation the ratio R = σL(epϱ0)/σT(epϱ0) is found to be 0.30 ± 0.14 at 〈Q2〉 = 0.6 GeV2, 〈W〉 = 2.3 GeV.

6.3 GeV Topological and reaction cross sections

Abstract From measurements of the reaction ep→e π − Δ ++ near threshold the nucleon axial-vector form factor is determined, using the PCAC calculations by Adler and Weisberger. The results are consistent with form factor determinations from single pion electroproduction. A dipole fit yields m A = (1.18 ± 0.07) GeV.

Study of electroproduction with a streamer chamber for 0.3 < Q2 < 1.5 GeV2, mp ⩽ W < 2.8 GeV

Abstract The Q 2 dependence of σ (γvp→π − Δ ++ ) was measured. Close to threshold σ (γvp→π − Δ ++ ) is roughly proportional to 1/( m 2 ϱ + Q 2 ) 2 . The data are consistent with dominance of the contact term and imply that the contact term has the Q 2 dependence of the ϱ propagator.

Determination of the nucleon axial vector form-factor from πΔ electroproduction near threshold

Abstract Electroproduction of hadrons is studied in the kinematic region W Q 2 2 using the DESY streamer chamber. Prong cross sections, charged-particle multiplicities and inclusive π − distributions are presented. The average charged multiplicity is found to be independent of Q 2 in the Q 2 range studied here; however it is lower than in photoproduction. The fraction of forward π − is found to be significantly less in electroproduction than in photoproduction. The 〈 p ⊥ 2 〉 for inclusive π − is, for all x values, similar to that found in photoproduction.

Δ++π−-electroproduction near threshold and the Q2 dependence of the contact interaction

Qausi-elastic ω production by ep scattering in the kinematic region 0.3. 2.0 GeV consistent in both W and Q2 dependence with the predictions of a model based on one-pion exchange and diffraction.

Charged hadron multiplicities and inclusive π− distributions in inelastic ep scattering

Abstract The reaction γvp→pπ+π− was studied in the W, Q2 region 1.3 to 2.8 GeV, 0.3 to 1.4 GeV2 using the streamer chamber at DESY. An analysis of Δ++(1232) and Δ0(1232) production via γvp→Δπ is presented. The W dependence, production angular distribution and decay distribution of Δ++ in the channel Δ++π− is similar to that found in photoproduction. At small momentum transfers the Q2 dependence of Δ++ production follows that of the ϱ propagator as predicted by VDM; at large momentum transfer there is little Q2 dependence. The W dependence of Δ0 production and its ratio with respect to Δ++ production is similar to that found in photoproduction.

ω Meson production by virtual photons

Abstract Production and decay characteristics of electroproduced rho mesons were studied in the final state epπ + π − .

Δ(1232) production by virtual photons

Abstract We have measured the reaction γ p → p π + π − in the DESY 1 m Streamer Chamber. The dominant ϱ o production is analyzed in terms of various models.