arXiv subjects

E. Ihara

Publications and source records attributed to E. Ihara.

6 recordsLinked to original sources

arXiv2009

Polarization transfer measurements for $^{12}{\rm C}(\vec{p},\vec{n})^{12}{\rm N (g.s.},1^+)$ at 296 MeV and nuclear correlation effects

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.

nucl-ex↗

arXiv2008

Cross-sections and analyzing powers for $(p,n)$ reactions on ${}^{3}{\rm He}$ and ${}^{4}{\rm He}$ at 346 MeV

The cross-sections and analyzing powers for $(p,n)$ reactions on ${}^{3}{\rm He}$ and ${}^{4}{\rm He}$ have been measured at a bombarding energy of $T_p$ = 346 MeV and reaction angles of $θ_{\rm lab}$ = $9.4^{\circ}$--$27^{\circ}$. The energy transfer spectra for ${}^{3}{\rm He}(p,n)$ at large $θ_{\rm lab}$ ($\ge$ $16^{\circ}$) are dominated by quasielastic contributions, and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known $L$ = 1 resonances in ${}^{4}{\rm Li}$ are clearly observed near the threshold in the ${}^{4}{\rm He}(p,n)$ spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large $θ_{\rm lab}$ ($\ge$ $22^{\circ}$). The nuclear correlation effects on the quasielastic peak for ${}^{4}{\rm He}(p,n)$ are also discussed.

nucl-ex↗

arXiv2008

Complete set of polarization transfer coefficients for the ${}^{3}{\rm He}(p,n)$ reaction at 346 MeV and 0 degrees

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 $θ_{\rm lab}$ = $0^{\circ}$. The data are compared 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.

nucl-ex↗

arXiv2007

Study of nuclear correlation effects via 12C(p,n)12N(g.s.,1+) at 296 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 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.

nucl-ex↗

arXiv2007

Complete Set of Polarization Transfer Observables for the $^{12}{\rm C}(p,n)$ Reaction at 296 MeV and 0$^{\circ}$

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 $θ_{\rm lab}=0^{\circ}$. The total spin transfer $Σ(0^{\circ})$ 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.

nucl-ex↗

arXiv2006

Evidence for an alpha cluster condensed state in 16O(alpha,alpha') at 400 MeV

Inelastic $α$ scattering on 16O is studied at 400 MeV by using an ice target. Near the 4-alpha breakup threshold of 14.4 MeV, a broad peak is observed at an excitation energy of 13.6+/-0.2 MeV with a width of 0.6+/-0.2 MeV. The spin-parity is estimated to be 0+ from the momentum-transfer dependence. The observed width is significantly larger than those of the neighboring 0+ states indicating a state with a well-developed alpha cluster structure. The magnitude of the cross section is sensitive to the density distribution of the constituent alpha clusters. The observed cross section is consistent with the theoretical prediction for the alpha cluster condensed state characterized by its dilute density distribution with a large root-mean-square radius of about 4.3 fm.

nucl-ex↗