Continuum Random Phase Approximation Research Articles

Inclusive56Fe(νe,e−)56Cocross section

We study the ${}^{56}\mathrm{Fe}({\ensuremath{\nu}}_{e}{,e}^{\ensuremath{-}}{)}^{56}\mathrm{Co}$ cross section for the KARMEN neutrino spectrum. The Gamow-Teller contribution to the cross section is calculated within the shell model, while the forbidden transitions are evaluated within the continuum random phase approximation. We find a total cross section of $2.73\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}40}{\mathrm{cm}}^{2},$ in agreement with the data.

Cross sections for neutral-current neutrino-nucleus interactions: Applications for12Cand16O

We study quasielastic neutrino-nucleus scattering on ${}^{12}\mathrm{C}$ $\mathrm{and}{ }^{16}\mathrm{O}$ within a continuum random phase approximation (RPA) model. The RPA equations are solved using a Green's function approach with an effective Skyrme (SkE2) two-body interaction. Besides a comparison with existing calculations, we carry out a detailed study using various methods (Tamm-Dancoff approximation and RPA) and different forces (SkE2 and Landau-Migdal). We evaluate cross sections that may be relevant for neutrino nucleosynthesis.

Weak reactions on 12C within the continuum random phase approximation with partial occupancies

We extend our previous studies of the neutrino-induced reactions on 12C and muon capture to include partial occupation of nuclear subshells in the framework of the continuum random phase approximation. We find, in contrast to the work by Auerbach et al., that a partial occupation of the p 1 2 subshell reduces the inclusive cross sections only slightly. The extended model describes the muon capture rate and the 12C( ν e , e −) 12 N cross section very well. The recently updated flux and the improved model bring the calculated 12C( ν μ , μ −) 12 N cross section (≈ 17.5 × 10 −40 cm 2) and the data ((12.4 ± 0.3(stat.) ± 1.8(syst.) × 10 −40 cm 2) closer together, but does not remove the discrepancy fully.

Isoscalar spin excitation in90Zrand208Pb

Isoscalar spin-transfer excitations have been measured in ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ by inelastic scattering of vector and tensor polarized 400 MeV deuterons in an excitation energy range from 2.5 to 43 MeV and 2.3 to 23 MeV, respectively. For ${}^{90}\mathrm{Zr},$ spin excitations were found between 7.5 and 10.7 MeV and in a large structure in the continuum (18 to 28 MeV). For ${}^{208}\mathrm{Pb},$ spin excitations were found at 3.55 and 5.85 MeV, between 6.5 and 11 MeV, and spread over the continuum. Elastic scattering cross sections and vector and tensor analyzing powers were measured between 3.4 and $24\ifmmode^\circ\else\textdegree\fi{}$ for Zr and Pb, and optical potential parameters were derived. The experimental results are compared to DWIA/RPA calculations. The transition densities used are generated using the continuum random phase approximation.

Quasielastic K + scattering in nuclei

The quasielastic scattering kaon-nucleus experiment performed at BNL is analyzed in a finite nucleus continuum random phase approximation framework, treating the reaction mechanism in Glauber theory up to two-step inelastic processes. A good description of the data is achieved, also providing a useful constraint on the strength of the effective particle-hole interaction in the scalar-isoscalar channel at intermediate momentum transfers.

Measurements of the reactions12C(νe,e−)12Ng.s.and12C(νe,e−)12N*

Charged current reactions of nu_e on 12C have been studied using a mu decay-at-rest nu_e beam from the Los Alamos Meson Physics Facility. More than 500 events from the exclusive reaction 12C + nu_e -> e- + 12N g.s. were measured in a large Liquid Scintillator Neutrino Detector (LSND). The observed energy dependence of the cross section and the angular distribution of the outgoing electron agree well with theoretical expectations. Measurements are also presented for inclusive transitions to 12N excited states, 12C + nu_e -> e- + 12N and compared with theoretical expectations. Results are consistent with a recent Continuum Random Phase Approximation (CRPA) calculation.

QuasielasticK+-nucleus scattering

Quasielastic K{sup +}-nucleus scattering data at q=290, 390, and 480 MeV/{ital c} are analyzed in a finite nucleus continuum random phase approximation framework, using a density-dependent particle-hole interaction. The reaction mechanism is consistently treated according to Glauber theory, keeping up to two-step inelastic processes. A good description of the data is achieved, also providing a useful constraint on the strength of the effective particle-hole interaction in the scalar-isoscalar channel at intermediate momentum transfers. We find no evidence for the increase in the effective number of nucleons participating in the reaction which has been reported in the literature. {copyright} {ital 1997} {ital The American Physical Society}

Comparison of continuum random phase approximation and the elementary particle model for the inclusive muon neutrino reaction on 12C

We have shown previously that the continuum random phase approximation (CRPA) reproduces the muon capture rate on 12C and the inclusive 12C( ν e , e −) 12N cross section for Michel spectrum neutrinos, while it overestimates the inclusive 12C( ν μ , μ −) 12N cross section for the LAMPF pion decay-in-flight ν μ neutrino beam. On the other hand, the elementary particle model of Mintz and collaborators is in rough agreement with the ν μ LAMPF data using the muon capture rate as input. In this paper we show that the CRPA also consistently reproduces inelastic electron scattering data at the excitation energies in 12C probed by the LAMPF experiment. To understand the different results of the two models, we compare the assumptions of the elementary particle model with the results of the CRPA and discuss whether experiments can decide which of them is correct.

Continuum random phase approximation method applied to the inclusive transverse electron scattering response.

A continuum random phase approximation (RPA) method for evaluating the structure function of nuclear matter is developed, where exchange terms for any particle-hole interaction are explicitly included. The method is applied to the inclusive transverse quasielastic electron scattering response at momentum transfer ranging from q=300 to 550 MeV/c. The interaction employed is a ${\mathit{g}}^{\ensuremath{'}}$ Landau-Migdal constant plus a (\ensuremath{\pi}+\ensuremath{\rho})-meson exchange interaction. A comparison with the standard ring series is made showing that the inclusion of finite range effects in the exchange terms is necessary. \textcopyright{} 1996 The American Physical Society.

Differential cross sections for neutrino scattering on 12C.

Differential cross sections for neutrino scattering on $^{12}\mathrm{C}$ are calculated within the (continuum) random phase approximation model. The charged current (${\ensuremath{\nu}}_{\mathit{e}}$,${\mathit{e}}^{\mathrm{\ensuremath{-}}}$) and (${\ensuremath{\nu}}_{\mathrm{\ensuremath{\mu}}}$,${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$) capture reactions on $^{12}\mathrm{C}$ are measured by the LSND Collaboration at LAMPF. We investigate and discuss the merits of such studies, especially the information that can be extracted from data for differential neutrino scattering cross sections. \textcopyright{} 1996 The American Physical Society.

Glauber isovector spin responses for (p

The separated isovector spin-longitudinal and spin-transverse responses from a recent (p,n) quasifree experiment at 494 MeV are analyzed in a Glauber theory framework up to two-step contributions. Nuclear correlations are treated in the continuum random phase approximation, accounting for the spreading width of the particle-hole states. A good description of the spin-longitudinal response is achieved, hinting at some evidence of pionic effects in the quasielastic region. The spin-transverse response is underestimated and we show that multistep contributions, while sizable, are not sufficient to provide an explanation of the discrepancy.

Muon capture, continuum random phase approximation, and in-medium renormalization of the axial-vector coupling constant.

We use the continuum random phase approximation to describe the muon capture on C-12, O-16 and Ca-40. We reproduce the experimental total capture rates on these nuclei to better than 10% using the free nucleon weak form factors and two different residual interactions. However, the calculated rates for the same residual interactions are significantly lower than the data if the in-medium quenching of the axial-vector coupling constant is employed.

Quasielastic nuclear scattering: a Glauber analysis

The nuclear quasielastic response in a continuum random phase approximation framework is discussed. Both (p,n) and (p,p′) reactions are considered, including one- and two-step contributions within a Glauber description.

Neutrino-induced reactions on 12C within the continuum random phase approximation.

Motivated by recent experiments we have studied ${\ensuremath{\nu}}_{\mathit{e}}$ and ${\ensuremath{\nu}}_{\mathrm{\ensuremath{\mu}}}$ induced charged- and neutral-current reactions on $^{12}\mathrm{C}$ within the continuum random phase approximation employing two different residual interactions. We find good agreement with the measured cross sections for the ${\ensuremath{\nu}}_{\mathit{e}}$ reactions, while our calculation signficantly differs from recently measured ${\ensuremath{\nu}}_{\mathrm{\ensuremath{\mu}}}$ cross sections. Our calculation indicates that the measurements of the total $^{12}\mathrm{C}$(${\ensuremath{\nu}}_{\mathit{e}}$,${\mathit{e}}^{\mathrm{\ensuremath{-}}}$${)}^{12}$${\mathrm{N}}^{\mathrm{*}}$ cross sections are consistent with the total $^{12}\mathrm{C}$(\ensuremath{\mu},${\ensuremath{\nu}}_{\mathrm{\ensuremath{\mu}}}$${)}^{12}$${\mathrm{B}}^{\mathrm{*}}$ capture rate.

Continuum random phase approximation self-consistent approaches to the theory of isobaric analog resonances.

Two approaches (exact and approximate) to the isobaric analog resonance (IAR) theory within the random phase approximation in the continuum are considered. Both of them are based on the partial self-consistency condition which is the result of the isospin symmetry of the nuclear Hamiltonian. The evaluations of the IAR partial proton widths for near magic nuclei over a wide atomic mass region are performed. The results obtained within the framework of these approaches are compared with each other and with the experimental data. The method of the calculation of the Coulomb correction to the IAR transition density is also given.

Calculations on the giant-dipole resonance in the continuum random-phase approximation with a momentum-dependent interaction

A formulation of the continuum random-phase approximation (CRPA) nuclear response with a velocity-dependent residual interaction of the Skyrme type is presented. The inhomogeneous coupled-channel integro-differential equations obtained are modified so as to use the Lanczos method, by means of which they can be solved relatively easy. The CRPA method here presented can give information on the direct and statistical decay as well as their partial ph components. We apply the method to a detailed analysis of photonuclear reactions in 4He, 16O and 40Ca in the giant-dipole-resonance region. Total cross sections, contributions from direct emission and spreading as well as partial γp and γn emission ph components are calculated and compared to experimental data.

Quasielastic nuclear response.

We explore the nuclear responses at intermediate energies, particularly in the spin longitudinal and spin transverse isovector channels, within the continuum random phase approximation framework. We also employ an extension of the standard random phase approximation to account for the spreading width of the single particle states through the inclusion of a complex and energy-dependent nucleon self-energy. The nuclear responses are then used as the basic ingredient to calculate hadronic reactions in the Glauber theory framework. Here both one and two-step contributions to the multiple scattering series in the quasi-elastic peak region are taken into account. We find evidence for shell effects in the one-step response and a strong dependence on the momentum regime of the two-step contribution.

Role of strange quarks in quasielastic neutrino scattering.

Confirming our previous proposal, we show within a continuum random-phase approximation calculation that the ratio of proton-to-neutron neutrino-induced quasielastic yield is a sensitive way to determine the strange quark axial form factor of the nucleon. Particularly, we find that the ratio is virtually independent of final state interactions (accounted for by a finite-range force derived from the Bonn meson-exchange potential) and nuclear structure effects. We present the ratio calculated for the neutrino beam available in an experiment currently approved at LAMPF.

Inelastic neutrino scattering on nuclei and neutrino-nucleosynthesis

Within the Continuum Random Phase Approximation we have calculated neutral current cross sections for various neutrino-induced particle reactions on selected nuclei. These cross sections are important for the neutrino-nucleosynthesis in explosive supernova burning. As a byproduct we find that neutrinos and antineutrinos excite parts of the giant dipole resonance differently, with scattering on 16O showing the most noticeable deviations.

Simple approximation to continuum random phase approximation (RPA): Application to the giant dipole resonance in 16O

We implement a reaction-theory based version of the continuum random phase approximation (RPA) approach to the microscopic structure of nuclear giant resonances in its simplest form. This involves a discrete RPA diagonalization of standard size but involving complex matrices so as to account for single-particle resonance widths. Escape widths of individual resonant structures in the case of the giant E1 strength in 16O are obtained in reasonable agreement with available data. The overall strength distribution agrees with that obtained in full continuum RPA calculations.