Correlations In Light Nuclei Research Articles

Study of Short-Range nuclear Correlations in light nuclei using the BeAGLE event generator

Nuclear dynamics at short distances among nucleons is one of the most outstanding phenomena in nuclear physics. Understanding the role of QCD in generating nuclear forces is important for uncovering the underlying physics of Short-Range Correlations (SRCs). In recent years, SRCs has been observed from light to heavy nuclei using fixed target experiments at Jefferson lab via high energy electron-nucleus scattering. In this talk, I will talk about the opportunity of studying SRCs using light nuclei with collider experiments, e.g., the Electron-Ion Collider (EIC). The experimental technique of studying the light nuclei can be based on exclusive processes with tagging final-state particles, in order to fully control the initial state of the target wavefunction. In particular, incoherent diffractive production of J/\psiJ/ψ particle off deuteron will be presented. In addition, the spectral function in light nuclei has been recently modeled in the BeAGLE event generator, where the decay kinematics of the light nuclei and their influence on the very forward detector design at the EIC will be discussed.

Search for three-nucleon short-range correlations in light nuclei

We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nucleon (3N) correlation dominance. While contributions beyond those from stationary 2N- SRCs are observed, our data show that isolating 3N-SRCs is more complicated than for 2N-SRCs.

Tensor correlations in light nuclei with tensor-optimized antisymmetrized molecular dynamics

We investigate the light nuclei using the nucleon-nucleon interaction. We describe the tensor and short-range correlations with the new variational theory named “tensor-optimized antisymmetrized molecular dynamics” (TOAMD). In TOAMD, the correlation functions for the tensor force FD and the short-range repulsion FS and their multiples are multiplied to the AMD wave function and the total wave function is expressed as the sum of all the components. We take all the necessary matrix elements of many-body operators coming from the products of the multiple correlation functions and the Hamiltonian. We use the interaction AV8′ and discuss the effect of tensor and short-range correlations in the s-shell nuclei, 3H and 4He.

Universality of Short-Range Nucleon-Nucleon Correlations in Nuclei

We investigate the short-range correlations in light nuclei. The highly correlated many-body states are obtained with an explicitly correlated basis which enables us to get a precise solution of a many-body Schrodinger equation for a realistic interaction. We show two-body density distributions for the different spin-isospin channels calculated from three- and four-body states to investigate the short-range correlations between nucleon pairs. At distances below 1 fm a universal behavior is found which does not depend on the many-body states. The universality is also seen in high momentum components of the two-body momentum distributions.

Spatial particle correlations in light nuclei. I two-particle systems

Expressions for spatial two-particle correlations in an LS-coupled basis of the harmonic oscillator are used to display the probability distribution of two identical nucleons as a function of their relative distance and their distance from the center of the nucleus. It is shown that a two-nucleon state in the p shell with total orbital angular momentum L=0 and total spin S=0 contains a di-neutron and a cigar-like component with equal probability. This result can also be proven analytically with the use of angular correlation functions. Scattering of the nucleons from the p shell to other shells leads to the enhancement of the di-neutron configuration. A semi-quantitative application to 6He is presented which shows that the probability of the di-neutron configuration in the ground state is of the order of 60%. The long-term goal of this work is to obtain a geometric insight into the properties of nuclei with several nucleons in a valence shell.

Spatial particle correlations in light nuclei. II four-particle systems

The geometry of configurations of identical particles in a shell is extended from two to four particles. Results are derived for a general ℓ shell and particular attention is paid to the p shell (ℓ=1), which is of relevance for the nucleus 8He. Expressions are given for the angular probability density in terms of the six angles between pairs of position vectors of the particles. The analysis of the p shell reveals the existence of two classes of favored four-particle configurations, with three members each. The transition from one class to the other is governed by the nuclear dynamics and depends on the conflicting tendencies of the short-range nuclear interaction versus the spin–orbit splitting.

Universality of short-range correlations in light nuclei

In this contribution, we investigate the structure of short-range correlations in many-body states. We obtain the highly correlated many-body states with an explicitly correlated basis which enables us to get a precise solution of a many-body Schrödinger equation for a realistic interaction. We show two-body density distributions calculated from three- and four-body states to investigate the short-range correlations between nucleon pairs. At distances below 1 fm a universal behavior is found which does not depend on the many-body states. The universality is also seen in the high momentum components of the two-body momentum distributions.

Microscopic analysis of two-body correlations in light nuclei

Within a nonperturbative dynamical two-body approach — based on coupled equations of motion for the one-body density matrix and the two-body correlation function — we study the distribution of occupation numbers in a correlated system close to the groundstate, the relaxation of singleparticle excitations and the damping of collective modes. For this purpose the nonlinear equations of motion are solved numerically within a finite oscillator basis for the first time adopting shortrange repulsive and long-range attractive two-body forces. We find in all cases that the formation of long- and short-range correlations and their mixing is related to the long- and short-range part of the nucleon-nucleon interaction which dominate the resummation of loop or ladder diagrams, respectively. However, the proper description of relaxation or damping phenomena is found to require both types of diagrams as well as the mixed terms simultaneously.

Short-range correlations in light nuclei near the neutron drip line

The particular stability of light nuclei with N=2 Z near the neutron drip line is evidenced from binding energy analyses and discussed in view of triton correlations. Properties of nuclei with one or two extra neutrons are discussed on the same ground.

Mode-Mode Coupling Model for the Four-Body Correlations in Light Nuclei

The four-body correlations in light nuclei are investigated from a viewpoint of many-body theoretical description. The four-body scattering modes are described in the quadratic form of two-body scattering modes. The two effects of the ground-state correlations and of the many-j configurations are taken into account by the random phase approximation, on the assumption of the spherical single-particle field. This mode-mode coupling model, which leads to a unified picture for even nuclei near closed-shell nuclei, is applied to the study of the low-lying positive-parity states of even nuclei in Ca region. Fundamental aspect of the level structures in 44Ti, 44Ca, 36Ar and 36S is reproduced. The structure of the four-body eigenmodes and electric-transition properties are investigated.

Kinematically correct optical potentials

The Watson multiple scattering formalism for the optical potential describing elastic nucleon-nucleus scattering is developed while paying careful attention to the kinematics. No approximations are made in handling the recoil of the target nucleus so that internal and external energies can be uniquely separated. The resultant formalism allows a careful examination of the impulse, form-factor, and closure approximations without the confusion of the admixture of recoil energies; it also allows an explicit display of the nuclear correlations due to target recoil. With the many necessary (but incompletely understood) approximations explicity displayed, it appears that their confluence makes it unlikely that meaningful information about dynamical correlations in light nuclei can be obtained from elastic double-scattering experiments.

Alpha-Like Spatial Four-Body Correlations in Light Nuclei

Alpha-Like Spatial Four-Body Correlations in Light Nuclei

Four-body correlations in light nuclei: (I). First excited 0 + states in 16O and 40Ca

A new theory of treating the four-particle-four-hole excitations (with the ground-state correlations) in light, closed-shell nuclei is proposed by using the basic idea of a “two-step method” proposed by Eichler and Marumori. In the theory, four-body scattering correlations are taken up in the first step as the most important correlations in light nuclei, and the corresponding four-body scattering eigenmodes are constructed in the framework of the new Tamm-Dancoff approximation. The interaction between these eigenmodes are treated as the next step. Thus the four-particle-four-hole excitations in light, closed-shell nuclei are described by “phonons” composed of a correlated pair of the four-particle scattering eigenmode and the four-hole one. Here in part I, properties of the four body scattering eigenmodes are investigated in detail, and a close connection between the four-body scattering correlations and the α-cluster is clarified. As a result of the theory, it can be shown that the first excited 0 + states in 16O and 40Ca are mainly composed of the four-particle-four-hole excitations in the new Tamm-Dancoff sense. Essential ingredients to produce intrinsic deformations in the 0 + states are discussed.

On the Four-Body Correlations in Light Nuclei

On the Four-Body Correlations in Light Nuclei

Four-particle correlations in light nuclei (II)

The problem of two protons and two neutrons in an open shell with either pairing or contact interactions is studied. It is found that these interactions, which were equivalent for the two-neutron case, are no longer equivalent, contact interactions being stronger in four-particle configurations. The nucleus 32S, which is considered as formed of two clusters of four holes of the most general form, is then studied.

Four-particle correlations in light nuclei

It is proposed to use, for light nuclei, trial wave functions describing dynamically independent groups of four particles formed of two protons and two neutrons, each group being of the most general form. The usual methods of the pairing problem cannot be generalized to this case. A variational method adapted to this wave function is developed.

Charge symmetric pairing correlations in light nuclei

Charge symmetric pairing correlations in light nuclei

Photonuclear reaction (γ, np) and nucleon-nucleon correlations in light nuclei

The photonuclear reaction (γ, np) on light nuclei is considered on the model of independent pairs in order to obtain information about nucleon-nucleon correlations in the nucleus. A general expression for the effective cross section for the process under study is obtained. The O16(γ, np) and N14(γ, np) reactions are used to illustrate the fact that the energy dependence of the total cross section and distribution over the relative energies of the emitted nucleons are sensitive to changes of the parameters of the wave function of the correlated pair in the nucleus. The role of the four-nucleon correlations on the nucleus O16 is discussed for the process under study. The theory is compared with available experimental data.

Effect of quadrupole correlations in light nuclei

Quadrupole correlations of nucleons having equal energies are considered on the basis of the effective Hamiltonian describing the interaction of nucleon pairs. It is shown that the formation of quadrupole correlations in light nuclei is energetically favoured if the interaction among pairs is attractive. Certain laws in the binding energy of the last neutron in light nuclei are explained by taking into account pair and quadrupole correlations. A criterion obtained shows at what excess of the number of neutrons over that of protons in stable nuclei, as a result of the parting of the Fermi surfaces, some outer neutrons cease to participate in quadruple correlations, which leads to the disappearance of explicit α-particle properties of nuclei.