Dynamics of the quasielastic O 16 ( e , e ′ p ) reaction at Q 2 ≈ 0.8 ( GeV ∕ c ) 2

Le résumé fourni par la source

The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed investigation of the $^{16}\mathrm{O}(e,{e}^{\ensuremath{'}}p)$ reaction in quasielastic, constant $(q,\ensuremath{\omega})$ kinematics at ${Q}^{2}\ensuremath{\approx}0.8\phantom{\rule{0.3em}{0ex}}{(\mathrm{GeV}∕c)}^{2}$, $q\ensuremath{\approx}1\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}∕c$, and $\ensuremath{\omega}\ensuremath{\approx}445\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. Use of a self-calibrating, self-normalizing, thin-film waterfall target enabled a systematically rigorous measurement. Five-fold differential cross-section data for the removal of protons from the $1p$-shell have been obtained for $0<{p}_{\mathrm{miss}}<350\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕c$. Six-fold differential cross-section data for $0<{E}_{\mathrm{miss}}<120\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ were obtained for $0<{p}_{\mathrm{miss}}<340\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕c$. These results have been used to extract the ${A}_{LT}$ asymmetry and the ${R}_{L}$, ${R}_{T}$, ${R}_{LT}$, and ${R}_{L+TT}$ effective response functions over a large range of ${E}_{\mathrm{miss}}$ and ${p}_{\mathrm{miss}}$. Detailed comparisons of the $1p$-shell data with Relativistic Distorted-Wave Impulse Approximation (RDWIA), Relativistic Optical-Model Eikonal Approximation (ROMEA), and Relativistic Multiple-Scattering Glauber Approximation (RMSGA) calculations indicate that two-body currents stemming from meson-exchange currents (MEC) and isobar currents (IC) are not needed to explain the data at this ${Q}^{2}$. Further, dynamical relativistic effects are strongly indicated by the observed structure in ${A}_{LT}$ at ${p}_{\mathrm{miss}}\ensuremath{\approx}300\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕c$. For $25<{E}_{\mathrm{miss}}<50\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and ${p}_{\mathrm{miss}}\ensuremath{\approx}50\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕c$, proton knockout from the $1{s}_{1∕2}$-state dominates, and ROMEA calculations do an excellent job of explaining the data. However, as ${p}_{\mathrm{miss}}$ increases, the single-particle behavior of the reaction is increasingly hidden by more complicated processes, and for $280<{p}_{\mathrm{miss}}<340\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕c$, ROMEA calculations together with two-body currents stemming from MEC and IC account for the shape and transverse nature of the data, but only about half the magnitude of the measured cross section. For $50<{E}_{\mathrm{miss}}<120\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and $145<{p}_{\mathrm{miss}}<340\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕c$, $(e,{e}^{\ensuremath{'}}pN)$ calculations which include the contributions of central and tensor correlations (two-nucleon correlations) together with MEC and IC (two-nucleon currents) account for only about half of the measured cross section. The kinematic consistency of the $1p$-shell normalization factors extracted from these data with respect to all available $^{16}\mathrm{O}(e,{e}^{\ensuremath{'}}p)$ data is also examined in detail. Finally, the ${Q}^{2}$-dependence of the normalization factors is discussed.

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