Cross sections and analyzing powers for ($\vec{p},np$) reactions of ${}^2\mathrm{H}, {}^6\mathrm{Li}$, and ${}^{12}\mathrm{C}$ at 296 MeV

We report measurements of cross sections and analyzing powers for nucleon-knockout $(\vec{p},np)$ reactions of ${}^2\mathrm{H}, {}^6\mathrm{Li}$, and ${}^{12}\mathrm{C}$ at 296 MeV using the RCNP NPOL3 neutron detector and large acceptance spectrometer. The $1s$ and $1p$ knockout reactions were successfully separated with a separation-energy resolution of approximately 6 MeV. The resulting data were compared with plane-wave and distorted-wave impulse approximation calculations employing the nucleon-nucleon $t$ matrix in free space. No significant differences were identified in the case of the present analyzing power data, in contrast to the significant reductions observed in $(\vec{p},2p)$ values. The conventional Pauli blocking and nuclear binding effects with the $g$ matrix and the relativistic effect of nucleon mass reduction in the nuclei are also discussed.

Figure 1

Schematic view of the NPOL3 neutron detector system.

Figure 2

Neutron kinetic energy $T_n$ values measured by the NPOL3 versus proton kinetic energy $T_p$ values determined by the LAS for the $(p,np)$ reaction of ${\mathrm{CD}}_2$ (deuterated polyethylene) at $T_0=296\mathrm{MeV}$. The color scale (gray scale) is logarithmic.

Figure 3

Separation-energy spectrum for the $(p,np)$ reaction of ${\mathrm{CD}}_2$ (deuterated polyethylene) at $T_0=296\mathrm{MeV}$. The shaded area corresponds to the background from chance coincident events. See text for details.

Figure 4

(a) Cross sections and (b) analyzing powers for the $1s$ knockout ${}^2\mathrm{H}(p,np)$ reaction at $T_0=296\mathrm{MeV}$ as functions of both the neutron energy $T_n$ and the recoil momentum $p_B$. The solid curves represent the results of PWIA calculations. The shaded area represents the fitting uncertainty of the cross sections. See text for detail.

Figure 5

Separation-energy spectra for (a) ${}^6\mathrm{Li}(p,np)$ and (b) ${}^{12}\mathrm{C}(p,np)$ reactions at $T_0=296\mathrm{MeV}$. The dashed curves represent the fits to the individual peaks and the solid curve shows the sum of the peak fitting.

Figure 6

Cross sections (upper panels) and analyzing powers (lower panels) for (a) $1p$ and (b) $1s$ knockout ${}^6\mathrm{Li}(p,np)$ reactions at $T_0=296\mathrm{MeV}$ as functions of both the neutron energy $T_n$ and the recoil momentum $p_B$. The solid, dashed, and dotted curves show the results of DWIA calculations using the free $NN t$-matrix, whereas the dot-dashed curves are the DWIA results employing the effective $NN g$-matrix. The shaded areas represent the fitting uncertainties of the cross sections. See text for detail.

Figure 7

The same data as in Fig. 6, but for (a) $1p$ and (b) $1s$ knockout ${}^{12}\mathrm{C}(p,np)$ reactions.

Figure 8

Ratios of the neutron spectroscopic factors $S(p,np)$ determined from the $(p,np)$ reaction relative to the relevant proton spectroscopic factors $S(e,e^{\prime }p)$ obtained from the $(e,e^{\prime }p)$ reaction as a function of incident energy $T_0$. The shaded boxes represent the uncertainties of $S(e,e^{\prime }p)$.

Figure 9

Analyzing power for the $1s$ knockout $(p,np)$ reactions at $T_0=296\mathrm{MeV}$ and $({\theta }_n,{\theta }_p)=(22.0^{\circ },65.0^{\circ })$ as a function of effective mean density $\overline{\rho }$. The solid and dashed lines represent the DWIA and PWIA predictions based on the free $NN t$-matrix, whereas the dot-dashed line denotes the DWIA prediction based on the effective $NN g$-matrix.

Figure 10

Comparison of the data for (a) the present $(p,np)$ reaction and (b) the $(p,2p)$ [17] reaction with the PWIA predictions based on the free nucleon mass $M_N$ (dot-dashed) and effective nucleon mass $M_N^{*}$ (dashed). The solid lines represent the predictions employing both $M_N^{*}$ and medium modified meson masses $m^{*}$ and coupling constants $g^{*}$. The unfilled boxes denote the data for free $NN$ scattering [78]. See text for detail.