Set Of Polarization Transfer Observables Research Articles

Complete set of polarization transfer observables for the16O(p⃗,n⃗)16F reaction at 296 MeV and 0 degrees

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.

Study of spin-dipole strengths in 16F via complete polarization transfer measurements

A complete set of polarization transfer observables has been measured for the 16O(p, n) reaction at Tp = 296 MeV and θlab = 0°. The measured polarization transfer observables are used in order to investigate the spin-parity of the spin-dipole resonance in 16F. A possible indication of 0− state has been found at Ex = 11.0 MeV. The obtained results also show the energy hierarchy Ex(2−) < Ex(0−) < Ex(l−), which suggests the importance of the tensor correlations.

Complete Set of Polarization Transfer Observables for the12C(p,n) Reaction at 296 MeV and 0°

A complete set of polarization transfer observables has been measured for the 12 C( p , n ) reaction at T p =296 MeV and θ lab =0°. The measured polarization transfer observables indicate that the spin–dipole resonance at E x ≃7 MeV has greater 2 - strength than 1 - strength, which is consistent with recent experimental and theoretical studies. The total spin transfer Σ(0°) deduced from the polarization transfer observables indicates a predominance of the spin-flip strength in the continuum. The exchange tensor interaction at a large momentum transfer of Q ≃3.6 fm -1 is discussed.

Total Spin Transfer in Continuum for90Zr(p,n) Reaction at 295 MeV

A complete set of polarization transfer observables has been measured for the 90 Zr( p , n ) reaction at T p = 295 MeV and θ lab = 0°. The measurement can yield the total spin transfer Σ(0°) which is independent of nuclear reaction mechanisms such as the effective nucleon–nucleon interaction or distortions. The deduced Σ(0°) values indicate the strong spin-flip characteristics of the continuum up to 50 MeV excitation. A predominance of unnatural-parity transitions in the continuum is also observed from polarization transfer observables.

Polarization transfer in quasifree(p→,n→)reactions on2Hand3,4Hetargets at 197 MeV

In this paper, we present a complete set of polarization-transfer observables measured at 197 MeV in the quasifree region for $(\stackrel{\ensuremath{\rightarrow}}{p},\stackrel{\ensuremath{\rightarrow}}{n})$ reactions on ${}^{2}\mathrm{H}$ and ${}^{3,4}\mathrm{He}$ targets. Data were obtained at laboratory scattering angles of $13\ifmmode^\circ\else\textdegree\fi{},$ $24\ifmmode^\circ\else\textdegree\fi{},$ $37\ifmmode^\circ\else\textdegree\fi{},$ and $48\ifmmode^\circ\else\textdegree\fi{}$ for the ${}^{2}\mathrm{H}$ target and at $13\ifmmode^\circ\else\textdegree\fi{}$ and $37\ifmmode^\circ\else\textdegree\fi{}$ for the ${}^{3,4}\mathrm{He}$ targets. The data span an energy-loss range up to 150 MeV, with a corresponding momentum-transfer range $q=0.75--2.4 {\mathrm{fm}}^{\ensuremath{-}1}.$ The polarization-transfer observables are used to calculate the center-of-mass polarization observables. The empirical results for the ${}^{2}\mathrm{H}$ target are compared to the observables obtained from the free nucleon-nucleon database and with Faddeev-type calculations. No discernible differences are observed in either the values of polarization-transfer observables or in the center-of-mass polarization observables among the three nuclei studied in this paper.

Gamow–Teller strength in the continuum and quenching problem

Abstract Differential cross sections at θlab = 0.0°–12.3° and a complete set of polarization transfer observables at θlab = 0.0° are measured for the 90Zr(p, n) reaction at Tp = 295 MeV. A multipole decomposition (MD) technique is applied to the cross sections to extract partial cross sections σL with L=0, 1, 2, and 3 contributions. A significant amount of σL=0 is found in the highly excited continuum region. After subtracting the estimated iso-vector spin-monopole strength from σL=0, the Gamow-Teller (GT) strength B(GT) is deduced to be Sβ− = Σ B(GT) = 28 ± 1.6 ± 5.4. The total spin transfer Σ(0°) which is independent of the nuclear reaction mechanisms such as the effective nucleon-nucleon interaction or distortions is derived from the complete set of polarization transfer observables. It is close to unity up to 50 MeV excitation indicating the strong spin-flip character of the continuum. By using the relation between the polarization transfer observables the fractions of natural-parity and unnatural-parity transitions are also obtained and the dominance of unnatural-parity transitions in the continuum is found. These results are consistent with those derived from the MD analysis. The Sβ− − Sβ+ value is 27.1 and this is 90% of Ikeda's sum rule value of 3(N - Z)=30. Consequently it is concluded that the quenching of the GT strength is small and the quenching mechanism due to the ΔN− admixture seems to play a minor role.

Observation of the spin isovector monopole resonance using thePb(p→,n→)Bireaction at 795 MeV

We examine a broad resonance in the $0\ifmmode^\circ\else\textdegree\fi{}$ ${}^{208}\mathrm{Pb}{(p,n)}^{208}\mathrm{Bi}$ and ${}^{90}\mathrm{Zr}{(p,n)}^{90}\mathrm{Nb}$ cross section spectra obtained at 795 MeV incident energy that appears at 32 MeV excitation energy in ${}^{208}\mathrm{Bi}$ and ${}^{90}\mathrm{Nb}.$ Earlier data taken at 200 MeV incident energy using the same reactions show no evidence for this resonance. We present theoretical results indicating that the spin isovector monopole predicted at this excitation energy is barely excited at 200 MeV while it is strongly excited at the higher energy. To further investigate this structure we have measured the first complete set of polarization-transfer observables for ${}^{\mathrm{nat}}\mathrm{Pb}$ at $0\ifmmode^\circ\else\textdegree\fi{}$ using the $(\stackrel{\ensuremath{\rightarrow}}{p},\stackrel{\ensuremath{\rightarrow}}{n})$ reaction at 795 MeV. The data show this resonance is predominantly a spin flip $\ensuremath{\Delta}S=1$ excitation giving strong supporting evidence for assigning this resonance as the spin isovector monopole.

Gamow-teller strength in the continuum and quenching problem

Differential cross sections at θ lab = 0.0° – 12.3° and a complete set of polarization transfer observables at θ lab = 0.0° are measured for the 90 Zr( p,n ) reaction at T p = 295 MeV. A multipole decomposition analysis (MDA) technique is applied to the cross sections to deduce the Gamow-Teller (GT) strength B (GT). The obtained S β − = Σ B (GT) value is 28.0 ± 1.6. The total spin transfer Σ is obtained for the continuum by using polarization transfer measurements. The S β − — S β + value is deduced to be 27.0 and this is 90% of Ikeda's sum rule value of 3( N — Z )=30. Thus the quenching of the GT strength is small and the quenching mechanism due to the ΔN − admixture seems to play a minor role.

Gamow-Teller strength in the continuum and quenching problem

Differential cross sections at θ lab = 0.0°–12.3° and a complete set of polarization transfer observables at θ lab = 0.0° are measured for the 90Zr( p, n) reaction at T p = 295 MeV. A multipole decomposition (MD) technique is applied to the cross sections to extract partial cross sections σ L with L=0, 1, 2, and 3 contributions. A significant amount of σ L=0 is found in the highly excited continuum region. After subtracting the estimated iso-vector spin-monopole strength from σ L=0 , the Gamow-Teller (GT) strength B(GT) is deduced to be S β − = Σ B(GT) = 28 ± 1.6 ± 5.4. The total spin transfer Σ(0°) which is independent of the nuclear reaction mechanisms such as the effective nucleon-nucleon interaction or distortions is derived from the complete set of polarization transfer observables. It is close to unity up to 50 MeV excitation indicating the strong spin-flip character of the continuum. By using the relation between the polarization transfer observables the fractions of natural-parity and unnatural-parity transitions are also obtained and the dominance of unnatural-parity transitions in the continuum is found. These results are consistent with those derived from the MD analysis. The S β − − S β + value is 27.1 and this is 90% of Ikeda's sum rule value of 3( N - Z)=30. Consequently it is concluded that the quenching of the GT strength is small and the quenching mechanism due to the ΔN − admixture seems to play a minor role.

Quasifree polarization-transfer measurements in the (p

A complete set of polarization transfer observables for quasifree scattering in the ({rvec p}, {rvec n}) reaction at 495 MeV is reported. Measurements were carried out on CD{sub 2}, natural carbon, and calcium targets at a momentum transfer of 1.72 fm{sup {minus}1} using the new Neutron Time-of-Flight facility at LAMPF. The spin-longitudinal and spin-transverse responses are extracted from the data. The ratio of these responses are compared to DWIA-RPA calculations in which the particle-hole interaction is taken to be of the form g{prime}+{pi}+{rho}. No evidence for these RPA correlations is seen in the data at this momentum transfer. 8 refs., 2 figs.

Continuum polarization transfer in 500 MeV proton scattering and pionic collectivity in nuclei.

A complete set of polarization transfer observables was measured for inclusive 500 MeV proton scattering from $^{2}\mathrm{H}$, Ca(nat.), and Pb(nat.) at ${\mathrm{theta}}_{\mathrm{lab}}$=18.5\ifmmode^\circ\else\textdegree\fi{} (q=1.75 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$). The excitation energy ranged over the entire quasielastic peak from 20 to 100 MeV. Longitudinal and transverse spin-flip probabilities were extracted from the data. These have simple model-dependent connections to the spin-longitudinal and transverse response functions for the heavy targets. Detailed analysis of the data reveals no evidence for collective enhancement in the spin-longitudinal response function. The relation of this analysis to the interpretation of the European Muon Collaboration effect in terms of excess pions is discussed in detail.