Nuclear Spin-isospin Response Research Articles

Nuclear Spin-Isospin Response within the Fayans Functional

Nuclear Spin-Isospin Response within the Fayans Functional

Nuclear Spin-Isospin Response within the Fayans Functional

An effective approximation to a fully self-consistent global description of the total force function of b decay within the framework of the theory of finite Fermi systems is presented, based on the calculation of ground states within the framework of the modified energy density functional of Fayans et al. (DF3-f) and the continuum quasiparticle random phase approximation (CQRPA). The isovector parameter ℎ2− of the volume part of the functional has been refined, the permissible range of which was determined earlier by us from restrictions on the parameters of the equation of state for nuclear matter—the symmetry energy and its derivative at equilibrium density, obtained from a joint analysis of the value of the ‘‘neutron skin’’ ΔRnp of the nuclei 208Pb and 48Ca, found in the PREX-II and CREX experiments, results of ab initio calculations of the properties of the ground states of nuclei with the interaction of N3LO and systematics of data on the masses of neutron stars from astrophysical observations. New calculations of the Gamow–Teller strength functions for the reference doubly magic nuclei 208Pb and 132Sn, as well as for the nucleus 130Sn with developed neutron pairing have been carried out. In the proposed model, the global DF3-a + CQRPA calculations of beta-decay half-lives of heavy (quasi)spherical nuclei with Z = 81–83 and T1/2 240 s are conducted. Experimental lifetimes are described with accuracy up to factor 5.

Systematic study of Δ (1232) resonance excitations using single isobaric charge-exchange reactions induced by medium-mass projectiles of Sn

The fragment separator FRS has been for the first time used to measure the (n,p) and (p,n)-type isobaric charge-exchange cross sections of stable 112,124Sn isotopes accelerated at 1A GeV with an uncertainty of 3% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic contribution can be associated to the excitation of isobar {\Delta}(1232) resonances and to the pion emission in s-wave, both in the target and projectile nuclei, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. The data lead to interesting results where we observe a clear quenching of the quasi-elastic component and their comparisons to theoretical calculations demonstrate that the baryonic resonances can be excited in the target and projectile nuclei. To go further in this investigation, we propose to study the excitation of baryonic resonances taking advantage of the combination of high-resolving power magnetic spectrometers with the WASA calorimeter. These new measurements will allow us to determine the momenta of the ejectiles and pions emitted in coincidence after the single isobaric charge-exchange collisions, providing us unique opportunities to study the evolution of the baryonic resonance dynamics with the neutron-proton asymmetry through the use of exotic radioactive ion beams.

Study of Δ excitations in medium-mass nuclei with peripheral heavy ion charge-exchange reactions

Isobaric single charge-exchange reactions, changing nuclear charges by one unit but leaving the mass partitions unaffected, have been for the first time investigated by peripheral collisions of 112Sn ions accelerated up to 1A GeV at the GSI facilities. The high-resolving power of the FRS spectrometer allows us to obtain (p,n)-type isobaric charge-exchange cross sections with an uncertainty of 3.5% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic component is associated to the excitation of the Δ(1232) isobar resonance and the emission of pions in s-wave both in the target and projectile nucleus, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. An apparent shift of the Δ-resonance peak of ∼63 MeV is observed when comparing the missing-energy spectra obtained from the measurements with proton and carbon targets. A detailed analysis, performed with a theoretical model for the reactions, indicates that this observation can be simply interpreted as a change in the relative magnitude between the contribution of the excitation of the resonance in the target and in the projectile.

Temperature dependence of nuclear spin-isospin response and beta decay in hot astrophysical environments

A microscopic approach to the proton-neutron nuclear response is formulated in the finite-temperature relativistic nuclear field theory framework. The approach is based on the meson-nucleon Lagrangian of quantum hadrodynamics and advances the relativistic field theory for spin-isospin response beyond the finite-temperature random phase approximation. The dynamical contribution to the in-medium proton-neutron interaction amplitude is described in a parameter-free way by the coupling between the single nucleons and strongly-correlated particle-hole excitations (phonons) within the newly developed finite-temperature formalism. In this framework we investigate temperature dependence of the Gamow-Teller and spin dipole resonances in the closed-shell nuclei 48Ca, 78Ni, and 132Sn. Broader impacts of their temperature dependence are illustrated for the associated beta decay rates and lifetimes of 78Ni and 132Sn in hot astrophysical environments. We found a remarkable sensitivity of the beta decay rates to the enhanced low-energy spin-isospin strength at finite temperature, in particular, to the contribution of the first-forbidden transitions.

Isospin transfer modes in exotic nuclei

This work presents an approach to nuclear spin-isospin response, which is capable of describing the overall strength distribution up to high excitation energies, including the fine structure of the low-lying strength, and resolving the long-standing quenching problem. The model is a covariant realization of the nuclear field theory and based on the self-consistent extensions of the covariant energy density functional (CEDF) theory. Results of the recent calculations for spin-isospin response of ordinary and exotic medium-mass nuclei are presented and discussed.

New Experimental Studies of Nuclear Spin-Isospin Responses

Possible directions of nuclear spin-isospin response studies are discussed. They includes i) light-ion induced charge exchange reaction studies in inverse-kinematics experiments with RI-beams, ii) studies with heavy-ion stable-beam induced charge exchange reactions, and iii) studies with RI-beam induced charge exchange reactions. Among them, RI-beam induced charge exchange reactions have unique properties which are missing in stable-beam induced reactions and can be used to reveal new aspects of spin-isospin responses in nuclei. Several experiments have been done and are planned with the SHARAQ spectrometer at RI Beam Factory, by utilizing the unique properties.

Neutrino studies in nuclei and intense neutrino sources

Nuclei are used as micro laboratories for studying fundamental properties of neutrinos and weak interactions. Nuclear responses for neutrinos are crucial for neutrino studies in nuclei. The responses, which are mainly nuclear spin isospin responses, are studied indirectly by charge exchange hadronic reactions for charged current responses, and photo nuclear reactions for neutral current responses. Intense neutrino sources provided by stopped pions from intense proton beams are very promising probes for studying directly nuclear weak responses. SNS/ORLaND and JHP combined with large neutrino detectors such as MOON are of potential interest for nuclear response studies with intense neutrino beams.

Nuclear spin responses for neutrinos and neutrino studies in 100Mo

Neutrino masses and mixings, which are key issues of neutrino physics, are studied by investigating low energy neutrinos (λ’s) in nuclei as micro-laboratories. Nuclear spin isospin responses for λ’s are crucial for λ studies in nuclei. Nuclear charge-exchange spinflip reactions are shown to be used for investigating nuclear spin isospin responses. Brief discussions are given on recent studies of nuclear spin isospin responses for low energy λ’s such as solar and supernova λ’s, and for λ’s associated with double beta decays (ββ). 100Mo is found to have large spin isospin responses for these low energy λ’s. Thus spectroscopic studies of ββ decays with a sensitivity of (m λ)≈0.03 eV and realtime studies of low energy solar λ’s are possible by MOON (Mo Observatory of Neutrinos) with multiton 100Mo.

Nuclear Responses for Neutrinos and Mo Observatory of Neutrinos

Nuclear responses for neutrinos and neutrino studies in Mo nuclei are briefly reported. Nuclear spin-isospin responses for neutrinos are crucial for neutrino studies in nuclei. Spin-isospin responses for solar neutrinos, supernova neutrinos and neutrinos involved in double-beta decays are discussed. It is of great interest to study neutrino masses and low energy solar neutrinos. It is shown that it is possible to carry out with 100Mo both spectroscopic studies of double-beta decays with the sensitivity of the order of 〈mν〉 ≈ 0.03eV and real-time exclusive studies of the low energy solar neutrinos.

Spin isospin giant resonances and neutrino nuclear responses

Recent studies on nuclear spin isospin giant resonances and nuclear spin isospin responses for neutrinos are briefly summarized. Subjects discussed include i) experimental probes for nuclear spin isospin modes, ii) microscopic structures of spin isospin giant resonances, iii) spin isospin strengths and isobars, and iv) nuclear spin isospin responses for solar-ν and ββ - ν.

Nuclear Spin Responses for Neutrinos in Astroparticle Physics

Nuclear spin responses are of vital importance for studies of neutrinos, weakly interacting particles and of weak interactions in nuclei. The physics objectives are concerned with lepton nuclear physics within and beyond the standard theory. Here nuclei, which consist of elementary particles in good quantum (eigen) states, are used as excellent micro-laboratories for studying fundamental particles and interactions. Subjects discussed include neutrinos(ν) and weak interactions, weakly interacting massive particles as candidates for dark matters (DM), and other related problems. Experimental studies of them are made by investigating ultra rare nuclear processes at low background underground laboratories. Nuclear responses relevant to electroweak processes, neutrinos, and weakly interacting massive particles are discussed. Nuclear spin isospin responses associated with axial charged weak currents are investigated by using charge-exchange spin flip nuclear reactions at the RCNP ring cyclotron laboratory.

Quasifree (d

Experimental data on the nuclear spin-isospin response in the quasifree region, measured with the charge-exchange reaction (d\ensuremath{\rightarrow},2p${[}^{1}$${\mathit{S}}_{0}$]) at Laboratoire National Saturne, are presented. The use of a tensor-polarized beam enables us to separate the tensor analyzing powers ${\mathit{T}}_{20}$ and ${\mathit{T}}_{22}$. The present publication is intended to serve as a compilation of the complete set of quasifree data with the (d\ensuremath{\rightarrow}${,}^{2}$He) reaction at 1.6 GeV bombarding energy. Data for $^{12}\mathrm{C}$ are compared to calculated cross sections and tensor-analyzing powers. The cross section in the high-energy end of the quasielastic peak is underestimated, whereas the polarization observables are reasonably well reproduced. The distortion effects are, however, found to be large, suggesting that the (d\ensuremath{\rightarrow}${,}^{2}$He) reaction is not sensitive to spin correlations in the continuum.

Nuclear spin isospin responses in double beta decays and dark matter search

Recent studies on electron neutrinos by double beta decays (ββ) and spin-coupled dark matters (DM) are briefly described. Nuclear spin isospin responses in ββ and nuclear spin interactions with DM are discussed.

Nuclear spin and isospin excitations

A review is given of our present knowledge of collective spin-isospin excitations in nuclei. Most of this knowledge comes from intermediate-energy charge-exchange reactions and from inelastic electron- and proton-scattering experiments. The nuclear-spin dynamics is governed by the spin-isospin-dependent two-nucleon interaction in the medium. This interaction gives rise to collective spin modes such as the giant Gamow-Teller resonances. An interesting phenomenon is that the measured total Gamow-Teller transition strength in the resonance region is much less than a model-independent sum rule predicts. Two physically different mechanisms have been discussed to explain this so-called quenching of the total Gamow-Teller strength: coupling to subnuclear degrees of freedom in the form of $\ensuremath{\Delta}$-isobar excitation and ordinary nuclear configuration mixing. Both detailed nuclear structure calculations and extensive analyses of the scattering data suggest that the nuclear configuration mixing effect is the more important quenching mechanism, although subnuclear degrees of freedom cannot be ruled out. The quenching phenomenon occurs for nuclear-spin excitations at low excitation energies ($\ensuremath{\omega}\ensuremath{\sim}10\ensuremath{-}20$ MeV) and small-momentum transfers ($q\ensuremath{\le}0.5$ ${\mathrm{fm}}^{\ensuremath{-}1}$). A completely opposite effect is anticipated in the high ($\ensuremath{\omega}$, $q$)-transfer region ($0\ensuremath{\le}\ensuremath{\omega}\ensuremath{\le}500$ MeV, $0.5\ensuremath{\le}q\ensuremath{\le}3$ ${\mathrm{fm}}^{\ensuremath{-}1}$). The nuclear spin-isospin response might be enhanced due to the attractive pion field inside the nucleus. Charge-exchange reactions at GeV incident energies have been used to study the quasifree peak region and the $\ensuremath{\Delta}$-resonance region. An interesting result of these experiments is that the $\ensuremath{\Delta}$ excitation in the nucleus is shifted downwards in energy relative to the $\ensuremath{\Delta}$ excitation of the free proton. The physical origin of this shift is discussed, and it is shown that it may be related to the energy-dependent, attractive one-pion exchange interaction in the medium.

The nuclear response functions in inclusive processes

The nuclear response function at intermediate energies for inclusive processes is treated in the path integral formalism. The method is then applied to the nuclear charge response, as seen in the deep inelastic (e, e') scattering, which is shown to be depleted by the action of the pion. Also studied is the nuclear spin-isospin response to an hadronic probe in the framework of the random phase approximation (RPA) and of the one-step Glauber theory. A pion-induced softening of the spin-longitudinal response is obtained even at momentum transfers as large as 2.4 fm −1.

Interpretation of the polarization transfer measurement in the (p,p′) reaction onPb208

The results of the experiment of Carey et al. on the polarization transfer in the (p,p\ensuremath{'}) reaction on $^{208}\mathrm{Pb}$ are discussed with respect to their relevance for the absence or presence of collective effects in the nuclear spin-isospin response.

The interplay between nucleonic and nuclear spin-isospin excitations

Following a brief review of pion-nucleon coupling in relativistic quark models and the introduction of the Δ(1232) at the quark level, we develop the nuclear spin-isospin response function in a framework of nucleons and Δ′s interacting through exchange of mesons. The spin-isospin dependent particle-hole interaction will be elaborated and various different aspects of the Landau-Migdal parameter g′ for nucleons and Δ′s will be discussed. We summarize the evidence for broad Δ-hole states at high excitation energies (200–400 MeV). Then the impact of the existence of such Δ-hole excitations on the quenching of Gamow-Teller and magnetic isovector spin transitions at low energy is discussed in combination with conventional nuclear mechanisms like core polarization and ground state correlations.

Charge pion electroproduction a selective probe of nuclear spin-isospin responses

We study the reaction of pion electroproduction on nuclei in the quasi-elastic region. We show that detection of the pion in the direction of the virtual photon permits the separation of the longitudinal and transverse spin responses through a Rosenbluth plot. Emphasis is also put on consistency between medium effects and gauge invariance.