Ken Kawahigashi

Spin-isospin response functions in quasi-elastic region☆

Abstract We calculate the isovector spin-longitudinal and -transverse response functions R L and R T in the quasi-elastic region by means of a continuum RPA with the Δ-hole configurations. We treat the Landau-Migdal parameters g ′ NN , g ′ NΔ and g ′ ΔΔ independently. Effects of Δ and dependence on g ′s are studied. The spin-transverse structure function S T obtained by ( e , e ′) is compared with the results by various effective interactions. The cross sections as well as spin observables of ( p , n ) are calculated by DWIA. Distortion reduces the ratio R L / R T , though RPA makes it too large. Free response functions with distortion reproduce the observed ratio reasonably well.

Enhancement of pionic modes in the quasielastic region

We report an evidence for the precursor phenomena of the pion condensation, which is found in the enhancement of the spin longitudinal cross sections ID q of the quasielastic 12C, \(^{40} Ca(\vec p, \vec n)\), reactions at the incident energy 494 and 346 MeV around the momentum transfer q ≈ q c , the critical momentum of the pion condensation. We utilized the distorted wave impulse approximation incorporated with the continuum random phase approximation. We adjusted the Landau-Migdal parameters, g′ NN and g′ NΔ, and obtained g′ NN ≈ 0.6–0.7 and g′ N Δ ≈ 0.3–0.4, which are consistent with those obtained from the energy of the Gamov-Teller giant resonance and the quenching factor of the Gamov-Teller sum rule.

Momentum transfer dependence of spin isospin modes in quasielastic (p⃗,n⃗) reactions

A complete set of polarization transfer coefficients has been measured for quasielastic (p,n) reactions on 2H and 12C at a bombarding energy of 346 MeV and laboratory scattering angles of 16°, 22°, and 27°. The spin-longitudinal IDq and spin-transverse IDp polarized cross sections are deduced. The theoretically expected enhancement in the spin-longitudinal mode is observed. The observed IDq is consistent with the pionic enhanced IDq evaluated in a distorted wave impulse approximation (DWIA) calculation employing a random phase approximation (RPA) response function. On the contrary, the theoretically predicted quenching in the spin-transverse mode is not observed. The observed IDp is not quenched, but rather enhanced in comparison with the DWIA+RPA calculation.

Momentum Transfer Dependence of Spin Isospin Modes in the Quasielastic Region

A complete set of polarization transfer coefficients has been measured for the quasi‐elastic 12C(p,n) reaction at a bombarding energy of 345 MeV and laboratory scattering angles of 16°, 22°, and 27°. The spin‐longitudinal IDq and spin‐transverse IDp polarized cross sections are deduced. The theoretically expected enhancement in the spin‐longitudinal mode is observed. The observed IDq is consistent with the pionic enhanced IDq evaluated in a distorted wave impulse approximation (DWIA) calculation employing a random phase approximation (RPA) response function. On the contrary, the theoretically predicted quenching in the spin‐transverse mode is not observed. The observed IDp is not quenched, but rather enhanced in comparison with the DWIA+RPA calculation. Two‐step contributions are responsible in part for the enhancement of ID p.