B. Dickinson

Coincidence πo electroproduction experiments in the first resonance region at momentum transfers of 0.3, 0.45, 0.60, 0.76 (GeV/c)2

Abstract The reaction e−+p→e−+p+πo has been studied in the region of the first pion nucleon resonance. Four sets of data have been analysed at nominal values of the squared four-momentum transfer to the pion nucleon system, k2, of 0.3, 0.45, 0.6 and 0.76 (GeV/c)2. We present results on the variation with k2 of the multipole amplitudes M1+, E1+, S1+ which contribute to the resonant partial wave and we also discuss the behaviour of Eo+, So+ and M1− contributing to the S and P-wave backgrounds.

Electroproduction of single positive pions above the resonance region

In this letter we report results of measurements of the reaction e § above the resonance region for k ~ (four-momentum transfer squared to the proton) equal to 0.7 (GeV/c) ~ and a 7:+n invariant mass s 89 equal to 1.9 GeV/c ~. These results are part of a preliminary programme of coincidence electroproduction measurements to establish the contribution of different hadronie states to the deep continuum crosssection. The results are fitted with fixed-t dispersion relation calculations of DEVENISH and LYTH (1) which have shown the cross-sections to be very sensitive to the electromagnetic charge form factor of the pion. From these fits a value is deduced for the pion form factor at this value of k 2. ENGELS et al. (3) have shown that similar fixed-t dispersion relation calculations fit measurements of y q p + n + r : + at our value of s, with their calculation demonstrating the importance of the Born terms, in particular the pionpole term. The importance of the pion-pole term in eleetroproduction has also been remarked on by BERENDS (3) and by MANWEILER and SCHMII)T (4). The experinient was performed at the Daresbury electron synchrotron using a 4.5 GeV extracted beam with a typical intensity of 2-1012 electrons/s and a duty ratio between 5 and 10%. The electron beam was focused into a 7.5 cm liquid-hydrogen target with a spot size typically {0.2x0.1)em 2, and divergence (2• 2)mrad% The beam intensity was continuously monitored with a 17-layer secondary emission monitor, which had been calibrated relative to a Faraday cup. An identical dummy target cell was used to determine the empty-target contribution to the scattering. The scattered electron and produce4 =+-meson were detected in two similar magnetic spectrometers, each consisting of two half-quadrupoles and a bending magnet. Scintillation counter hodoscopes were used to measure the momentum and production angles of the produced particles. The electron spectrometer had a momentum acceptance of =~ 5% and a

Electroproduction of π+ mesons in the second and third resonance regions

Data are presented for the reaction ep → enπ+ at a nominal four-momentum transfer squared of 0.4 (GeV/c)2. The angular distribution of the π+ meson has been measured at angles up to 70° from the virtual photon direction for isobar masses in the range 1400 → 1600 MeV/c2 and, over a small angular range, close to the virtual photon direction for masses between 1600 MeV/c2 and 1860 MeV/c2. Clear evidence is seen for the presence of resonant helicity-12 amplitudes in both the second and third resonance regions. Some possible interpretations of the data are discussed.

Coincidence πo electroproduction in the second resonance region

Abstract The reaction e − + p → e − + p + π o has been studied in the region of the second pion nucleon resonance. Two sets of data have been taken and analysed at nominal values of the squared four momentum transfer to the pion nucleon system of 0.4 and 0.6 (GeV/ c ) 2 . A phenomenological interpretation of the data is presented. Our results are compared with the predictions of fixed- t dispersion relation calculations and with the symmetric quark model.

Electroproduction of πo mesons in the region of the first pion-nucleon resonance

The reaction e−+p→e−+p+πo has been studied in the π−N centre of mass range from 1130 to 1340 MeV/c2 by detecting the final proton in coincidence with the scattered electron. The four-momentum transfer to the pion-nucleon system was between 0.40 and 0.50 (GeV/c)2 and the polarisation of the exchanged virtual photon near unity. The proton angular distribution is analysed phenomenologically in terms of the multipoles M1+, E1+, S1+ contributing to the resonant partial wave and Eo+, So+ contributing to the s-wave background. The magnetic dipole excitation M1+ is shown to dominate the cross section but clear evidence is obtained for a significant contribution from the scalar multipole S1+.

COINCIDENCE ELECTROPRODUCTION ABOVE THE RESONANCE REGION.

Data has been obtained for coincidence electroproduction at an invariant hadronic mass, s12, of 1.93 GeV/c2, and four momentum transfer squared, |k2|, 0.7 (GeV/c)2. Electrons were detected in coincidence with forward produced π− and π+ mesons and forward and backward produced protons, for selected values of t, but almost the full range of kinematically available missing mass. We present cross sections for the exclusive reactions. γv+p → π+ + n, → π− + δ++, → p + ϱ0, and for the inclusive reactions, γv + p → π+ anything, → π− + anything, → p + anything.

Electroproduction of single pions near threshold

Inelastic electron scattering cross sections from hydrogen have been mea- sured near the pion production threshold at electron four-momentum transfers squared of 0.10, 0.14, 0.19 and 0.31 (GeV/c)2 using a beam of 2 GeV/c electrons from the Daresbury electron synchrotron and a magnetic spectrometer to detect the scattered electron. The results are analysed phenomenologically, and com- pared with theoretical calculations, using current algebra, to provide an estimate of the axial-vector form factor.

Electroproduction of π-Δ++(1236) from hydrogen at W = 1.9 GeV and -κ2 = 0.7 GeV2

Abstract We present cross sections for the electroproduction of the channel π − Δ ++ (1236) from hydrogen, i.e. for the virtual photoproduction process γ v p→ π − Δ ++ (1236) at W = 1.9 GeV, − κ 2 = 0.7 GeV 2 and with e = 0.85 for φ = 90°, 135° and 180° and 0.2 GeV 2 (0 ∗ . We show comparisons with the Born model of Berends and Gastmans [2] and with the vector-dominance model of Bartl and Schildknecht [3]. There is reasonable agreement between models and data except for the t -dependence of the Born model.

The correction of coincidence electron-scattering cross sections for radiative effects

Abstract The correction of inelastic electron-scattering cross sections for the effects of radiation is considered for experiments in which one of the final-state hadrons is detected in coincidence with the scattered electron. The results are expressed in terms of the missing mass of the unobserved particles. The accuracy of some commonly used approximations is investigated in the case of the ep → epπ0 reaction in the region of the Δ (1236) resonance.