Search

We measured the ${}^{12}\mathrm{C}{(e,e}^{\ensuremath{'}}p)$ cross section as a function of missing energy in parallel kinematics for $(q,\ensuremath{\omega})=(970 \mathrm{MeV}/c, 330 \mathrm{MeV})$ and $(990 \mathrm{MeV}/c, 475 \mathrm{MeV}).$ At $\ensuremath{\omega}=475 \mathrm{MeV},$ at the maximum of the quasielastic peak, there is a large continuum ${(E}_{m}g50 \mathrm{MeV})$ cross section extending out to the deepest missing energy measured, amounting to almost 50% of the measured cross section. The ratio of data to distorted-wave impulse approximation (DWIA) calculation is 0.4 for both p and s shells. At $\ensuremath{\omega}=330 \mathrm{MeV},$ well below the maximum of the quasielastic peak, the continuum cross section is much smaller and the ratio of data to DWIA calculation is 0.85 for the p shell and 1.0 for the s shell. We infer that one or more mechanisms that increase with $\ensuremath{\omega}$ transform some of the single-nucleon knockouts into a multinucleon knockout, decreasing the valence knockout cross section and increasing the continuum cross section.

We have measured the [sup 12]C([gamma][sup *],[pi][sup [minus]][ital p])[sup 11]C[sub g.s.] cross section using virtual bremsstrahlung at three points at invariant masses of 1444 and 1530 MeV. At low neutron initial momentum ([ital p][sub [ital m]][approx]60 MeV/[ital c]) and large [ital N][sup *] momentum ([ital p][sub [ital N]][sup *][approx]750 MeV/[ital c]) the measured cross section is at or below the distorted wave impulse approximation (DWIA) calculation. At larger initial momentum ([ital p][sub [ital m]][approx]220 MeV/[ital c]) and smaller [ital N][sup *] momentum ([ital p][sub [ital N]][sup *][approx]500 MeV/[ital c]), the measured cross section is almost twice as large as the DWIA calculation. This discrepancy might be due to [ital N][sup *]-nucleus interactions.

We have measured missing-energy spectra for the reaction {sup 12}C({ital e},{ital e}{prime}{ital p}) in the quasielastic region in parallel kinematics at momentum transfers {ital q} of 585, 775, and 827 MeV/{ital c}. We observed {sup 1}{ital p} and {sup 1}{ital s} single-proton knockout peaks and large broad strength attributed to multinucleon knockout. We saw no increase in strength at pion threshold. The ratio of single-particle knockout to a distorted-wave impulse-approximation calculation is approximately constant with {ital q}. Multinucleon knockout is 25%--40% of the total cross section; it increases with {ital q}. This quasielastic non-single-nucleon knockout is much stronger than previously observed.

Differential cross sections for $^{14}\mathrm{N}(\ensuremath{\gamma}, {\ensuremath{\pi}}^{+})^{14}\mathrm{C}(\mathrm{g}.\mathrm{s}.)$ (${0}^{+}$1) have been measured for an incident photon energy ${E}_{\ensuremath{\gamma}}=200$ MeV at laboratory angles of 45\ifmmode^\circ\else\textdegree\fi{}, 60\ifmmode^\circ\else\textdegree\fi{}, 75\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, 120\ifmmode^\circ\else\textdegree\fi{}, and 140\ifmmode^\circ\else\textdegree\fi{}. Momentum-space distorted-wave-impulse-approximation calculations, using a complete treatment of a one-body pion-photoproduction operator, are found to be in excellent agreement with the experimental data. The effect of the momentum-dependent terms in the nuclear photoproduction operator is observed. The reaction is found to be sensitive to input nuclear structure elements not observable in the ($e, {e}^{\ensuremath{'}}$) form-factor data.

The /sup 12/C(e,e'p) reaction at the delta resonance has been measured for protons detected parallel to the momentum transfer at two kinematical situations: at the maximum and the low-energy-loss side of the peak. The cross section was measured for missing energies up to 320 and 220 MeV, respectively. In the missing energy spectrum two distinct structures are observed, which correspond to multinucleon knockout and quasifree pion production processes. In addition, there is a remnant of the quasifree knockout process.

Differential cross sections for 14 N(γ, π + ) 14 C gs at a photon energy of 320 MeV, near the peak of the free nucleon delta resonance, have been measured at six angles ranging from 35° to 120°. Momentum-space calculations based on the distorted wave impulse approximation yield results which are lower than experiment by a factor of three.

The pion angular distribution for the /sup 16/O(..gamma..,..pi../sup +/) /sup 16/N reaction leading to the lowest quartet of states in /sup 16/N has been measured at 320 MeV photon energy. The results are compared with a distorted-wave impulse approximation calculation.

The inelastic electron-scattering cross sections of H, He, Be, C, and O were measured for 730-MeV electrons scattered at 37.1/sup 0/ for energy transfers to the nucleus up to 550 MeV. The nuclear response in the delta region is found to be quite similar for the A>1 targets. Although the differential cross section per nucleon at the peak of the delta region (380 MeV) is suppressed compared to that of the free nucleon, the area in the 230--550 MeV region is enhanced for the A>1 targets.

Inclusive cross sections for the proton and nuclear targets of A = 4, 9, 12, and 16 were measured for 537 and 730 MeV electrons scattered at 37.1 deg. Systematic features of the continuum scattering data are compared with other electron scattering data and with photoabsorption measurements. A model calculation based on the isobar-hole formalism is compared with the data in the delta resonance region.

The reaction $^{12}\mathrm{C}(e,{e}^{\ensuremath{'}}p)$ in the dip region ($\ensuremath{\omega}=200 \mathrm{MeV}, \mathrm{q}=400 \mathrm{Mev}c$) has been measured in parallel kinematics for missing energies up to 160 MeV. A coincidence yield considerably larger than that expected for a one-body reaction process is observed, though the one-body contribution from $p$- and $s$-shell knockout is also present. A uniform continuum strength extends from beyond the $p$ shell to the highest measured missing energies. This continuum strength is the dominant contribution to the ($e,{e}^{\ensuremath{'}}p$) reaction process in the dip region.