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Register a new userPolarization transfer measurements for $^{12}{rm C}(vec{p},vec{n})^{12}{rm N (g.s.},1^+)$ at 296 MeV and nuclear correlation effects
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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.
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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.
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 measured 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.
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 distorted 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.
We present first measurements of the double ratio of the polarization transfer components $(P^{prime}_{!x} !/ P^{prime}_{!z} )_p/ (P^{prime}_{!x} !/ P^{prime}_{!z} )_s$ for knock-out protons from $s$ and $p$ shells in $^{12}{rm C}$ measured by the $^{12}{rm C}(vec{e},{e}vec{p},)$ reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in relativistic distorted-wave impulse approximation. Our results show that differences between $s$- and $p$-shell protons, observed when compared at the same initial momentum (missing momentum) largely disappear when the comparison is done at the same proton virtuality. We observe no density-dependent medium modifications for protons from $s$ and $p$ shells with the same virtuality in spite of the large differences in the respective nuclear densities.
We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio $G^{n}_{E}/G^{n}_{M}$ was extracted from the beam-target vector asymmetry $A_{ed}^{V}$ at four-momentum transfers $Q^{2}=0.14$, 0.20, 0.29 and 0.42 (GeV/c)$^{2}$.
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