We report measurements of the cross section and a complete set of polarization transfer observables for the ${}^{16}{rm O}(vec{p},vec{n}){}^{16}{rm F}$ reaction at a bombarding energy of $T_p$ = 296 MeV and a reaction angle of $theta_{rm lab}$ = $0^{
circ}$. The data are compared with distorted-wave impulse approximation calculations employing the large configuration-space shell-model (SM) wave functions. The well-known Gamow-Teller and spin-dipole (SD) states at excitation energies of $E_x$ $lesssim$ 8 MeV have been reasonably reproduced by the calculations except for the spin--parity $J^{pi}$ = $2^-$ state at $E_x$ = 5.86 MeV. The SD resonance at $E_x$ $simeq$ 9.5 MeV appears to have more $J^{pi}$ = $2^-$ strength than $J^{pi}$ = $1^-$ strength, consistent with the calculations. The data show significant strength in the spin-longitudinal polarized cross section $ID_L(0^{circ})$ at $E_x$ $simeq$ 15 MeV, which indicates existence of the $J^{pi}$ = $0^-$ SD resonance as predicted in the SM calculations.
We performed the multipole decomposition analysis (MDA) for the ${}^{208}{rm Pb}(p,n)$ data in order to obtain the spin-dipole (SD) strengths separated into each $Delta J^{pi}$ contribution $dB({rm SD}_{Delta J^{pi}};omega)/domega$. The random phas
e approximation (RPA calculations reproduce the total SD strength reasonably well, whereas some discrepancies are found for separated SD strength. The centroids of the resonances are slightly lower and higher than the theoretical predictions for $1^-$ and $2^-$, respectively. These softening and hardening effects observed in $1^-$ and $2^-$ distributions would be due to the tensor correlation effects not included in the present RPA calculations.
Differential cross sections and complete sets of polarization observables are presented for the Gamow-Teller $^{12}{rm C}(vec{p},vec{n})^{12}{rm N}({rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV with momentum transfers $q$ of 0.1 to $2.2{
rm fm}^{-1}$. The polarization transfer observables are used to deduce the spin-longitudinal cross section, $ID_q$, and spin-transverse cross sections, $ID_p$ and $ID_n$. The data are compared with calculations based on the distorted wave impulse approximation (DWIA) using shell-model wave functions. Significant differences between the experimental and theoretical results are observed for all three spin-dependent $ID_i$ at momentum transfers of $q gtrsim 0.5{rm fm}^{-1}$, suggesting the existence of nuclear correlations beyond the shell model. We also performed DWIA calculations employing random phase approximation (RPA) response functions and found that the observed discrepancy is partly resolved by the pionic and rho-mesonic correlation effects.
We report measurements of the cross-section and a complete set of polarization transfer coefficients for the ${}^{3}{rm He}(p,n)$ reaction at a bombarding energy $T_p$ = 346 MeV and a reaction angle $theta_{rm lab}$ = $0^{circ}$. The data are compa
red with the corresponding free nucleon-nucleon values on the basis of the predominance of quasi-elastic scattering processes. Significant discrepancies have been observed in the polarization transfer $D_{LL}(0^{circ})$, which are presumably the result of the three-proton $T$ = 3/2 resonance. The spin--parity of the resonance is estimated to be $1/2^-$, and the distribution is consistent with previous results obtained for the same reaction at $T_p$ = 48.8 MeV.
We report measurements of the cross section and a complete set of polarization observables for the Gamow--Teller ${}^{12}{rm C}(vec{p},vec{n}){}^{12}{rm N}({rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV. The data are compared with disto
rted wave impulse approximation calculations employing transition form factors normalized to reproduce the observed beta-decay $ft$ value. The cross section is significantly under-predicted by the calculations at momentum transfers $q gtrsim $ 0.5 ${rm fm^{-1}}$. The discrepancy is partly resolved by considering the non-locality of the nuclear mean field. However, the calculations still under-predict the cross section at large momentum transfers of $q$ $simeq$ 1.6 ${rm fm^{-1}}$. We also performed calculations employing random phase approximation response functions and found that the observed enhancement can be attributed in part to pionic correlations in nuclei.
A complete set of polarization transfer observables has been measured for the $^{12}{rm C}(p,n)$ reaction at $T_p=296 {rm MeV}$ and $theta_{rm lab}=0^{circ}$. The total spin transfer $Sigma(0^{circ})$ and the observable $f_1$ deduced from the measure
d polarization transfer observables indicate that the spin--dipole resonance at $E_x simeq 7 {rm MeV}$ has greater $2^-$ strength than $1^-$ strength, which is consistent with recent experimental and theoretical studies. The results also indicate a predominance of the spin-flip and unnatural-parity transition strength in the continuum. The exchange tensor interaction at a large momentum transfer of $Q simeq 3.6 {rm fm}^{-1}$ is discussed.
