Conventional BCS,unconventional BCS,and non-BCS hidden dineutron phases in neutron matter

The nature of pairing correlations in neutron matter is re-examined. Working within the conventional approximation in which the nn pairing interaction is provided by a realistic bare nn potential fitted to scattering data, it is demonstrated that the standard BCS theory fails in regions of neutron number density, where the pairing constant λ, depending crucially on density, has a non-BCS negative sign. We are led to propose a non-BCS scenario for pairing phenomena in neutron matter that involves the formation of a hidden dineutron state. In low-density neutron matter, where the pairing constant has the standard BCS sign, two phases organized by pairing correlations are possible and compete energetically: a conventional BCS phase and a dineutron phase. In dense neutron matter, where λ changes sign, only the dineutron phase survives and exists until the critical density for termination of pairing correlations is reached at approximately twice the neutron density in heavy atomic nuclei.     

High-energy phenomena,short-range nuclear structure and QCD

A systematic review and theoretical analysis of the experimental data on multi GeV lepton, photon, hadron, deuteron (nucleus) reactions from nuclei forbidden in the case of scattering from free nucleons is presented. It is shown that all these data can be quantitatively described as a manifestation of short-range few nucleon correlations. Calculations for elastic and (deep)inelastic electromagnetic and weak form factors of the deuteron and other nuclei, are given. The inclusive production of leading particles in the nucleus fragmentation region in high-energy lepton, hadron or nucleus-induced collisions is analyzed. The straightforward correspondence between the Weinberg equation for the light-cone wave functions of the deuteron and the non-relativistic Schrödinger equation is found. It is shown that the predictions of quantum chromodynamics for short-distance phenomena in nuclei are in agreement both with experimental data and theoretical expectations due to short range correlations in nuclei. Several feasible experiments are considered which could establish the existence of relativistic nuclear physics.     

Do ordinary nuclei contain exotic states of matter?

The strongly repulsive core of the short-range nucleon-nucleon interaction leads to the existence of high-momentum nucleons in nuclei. Inclusive electron scattering can be used to probe these high-momentum nucleons and study the nature of the corresponding short-range correlations in nuclei. With recent data from Jefferson Lab we have begun to map out the strength of two-nucleon correlations in nuclei, while upcoming experiments should allow us to isolate the presence of multi-nucleon correlations. In addition to their importance in describing nuclear structure, these configurations of correlated nucleons represent high-density ‘droplets’ of hadronic matter. As the density of hadronic matter increases there should be a weakening of quark confinement, similar to the onset of deconfinement expected at extremely high temperatures. While there have been hints of non-hadronic structure in nuclei, future measurements will allow us to directly probe the quark distributions of high-density configurations in nuclei. A modified quark structure in these closely packed nucleons would provide a clear signature of exotic components to the structure of nuclei.     

A modified shell model for atomic nuclei

The shell model of spherical nuclei is updated by an approximate count of nucleon-nucleon correlations. A coordinated scheme for calculating the binding energy and nuclear radius is proposed. Good agreement with the experimental data on the binding energies of spherical even-even nuclei is attained.     

Calculations of the β-decay half-lives of neutron-deficient nuclei

In this work,β~+/EC decays of some medium-mass nuclei are investigated within the extended quasiparticle random-phase approximation(QRPA),where neutron-neutron,proton-proton and neutron-proton(np) pairing correlations are taken into consideration in the specialized Hartree-Fock-Bogoliubov(HFB) transformation.In addition to the pairing interaction,the Br¨uckner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions.Calculations are performed for even-even proton-rich isotopes ranging from Z =24 to Z =34.It is found that the np pairing interaction plays a significant role inβ-decay for some nuclei far from stability.Compared with other theoretical calculations,our calculations show good agreement with the available experimental data.Predictions of β-decay half-lives for some very neutron-deficient nuclei are made for reference.     

Short Range Correlations and Wave Function Factorization in Light and Finite Nuclei

Recent BNL and Jlab data provided new evidence on two nucleon correlations (2NC) in nuclei. The data confirm the validity of the convolution model, describing the spectral function (SF) of a correlated pair moving in the mean field with high and low relative and center-of-mass (cm) momenta, respectively. The model is built assuming that the wave function (WF) of a nucleus A, describing a configuration where the cm momentum of a correlated pair is low and its relative momentum is high, factorizes into the product of the two-body WF and that of the A-2 system. Such a factorization has been shown to occur in nuclear matter (NM). Here it is shown that few-body systems exhibit factorization, which seems to be therefore a general property, to be reproduced also in studies of the WF of finite nuclei.     

Fusability and fissionability in 86Kr-induced reactions near and below the fusion barrier

Evaporation-residue excitation functions for the reactions ⁸⁶Kr + ^70,76Ge, ^92,100 Mo, ^99,102,104 Ru have been measured using activation methods and the velocity filter SHIP. The data span the region from well below the fusion barrier up to, and beyond, the energy where limitation by fission competition takes place. The data are shown to be compatible with the concept of complete fusion followed by the statistical decay of the equilibrated compound nucleus. Information on both the fusion probability at and below the fusion threshold and the fissionability of the compound nuclei formed, is extracted. The model dependence of the extracted fission barriers is discussed in detail. In analogy to studies involving lighter projectiles, strong correlations between the low-energy nuclear-structure properties of the nuclei and the subbarrier fusion probability are found. A relative shift of the fusion barrier to higher energies, that increases with the number of valence neutrons in the target nuclei, is observed.     

Combinatorial nuclear level densities based on the Gogny nucleon-nucleon effective interaction

A combinatorial method to calculate total level densities from an arbitrary single-particle level scheme is presented. Parity, angular momentum, pairing correlations as well as collective enhancements are explicitly treated. This method is employed using single-particle level schemes obtained from Hartree-Fock-Bogoliubov calculations based on the Gogny effective interaction. Sixty five even-even nuclei with masses 26 ?A? 250 are considered. Rather good agreements are obtained when comparing our predictions with experimental data for energies of the order of the neutron binding energies and for low excitation energies where discrete levels are experimentally observed. Received: 13 February 2001 / Accepted: 24 September 2001     

Shell model Monte Carlo studies of N = Zpf-shell nuclei with pairing-plus-quadrupole Hamiltonian

We perform shell model Monte Carlo calculations of selected N = Z pf-shell nuclei with a schematic Hamiltonian containing isovector pairing and quadrupole-quadrupole interactions. Compared to realistic interactions, this Hamiltonian does not give rise to the SMMC “sign problem”, while at the same time resembles essential features of the realistic interactions. We study pairing correlations in the ground states of N = Z nuclei and investigate the thermal dependence of selected observables for the odd-odd nucleus ⁵⁴Co and the even-even nuclei ⁶⁰Zn and ⁶⁰Ni. Comparison of the present results to those with the realistic KB3 interaction indicates a transition with increasing temperature from a phase of isovector pairing dominance to one where isoscalar pairing correlations dominate. In addition, our results confirm the qualitative reliability of the procedure used to cure the sign problem in the SMMC calculations with realistic forces.     

Generalization of the N(p)N(n)N(p)N(n) scheme and the structure of the valence space

The N(p)N(n) scheme, which has been extensively applied to even-even nuclei, is found to be a very good benchmark for odd-even, even-odd, and doubly-odd nuclei as well. There are no apparent shifts in the correlations for these four classes of nuclei. The compact correlations highlight the deviant behavior of the Z = 78 nuclei and are used to deduce effective valence proton numbers near Z = 64 as well as to study the evolution of the Z = 64 subshell gap.     

Scales and Universality in Few-Body Systems

The role of scales in the physics of large few-body systems is reviewed. They are evidenced by considering weakly-bound three and four particles, where point-like interactions are regularized and renormalized in a procedure characterized by the emergence of physical scales fixed by observables. The results obtained with renormalized zero-ranged two-body interactions are presented in the form of universal scaling plots, or correlations between observables, where we also consider results of several other model calculations, as well as experimental results obtained in nuclear physics and cold-atom laboratories. The universal correlations between few-body observables are useful to predict one in terms of another observable and we discuss applications in setting low energies properties of halo nuclei, molecular and cold atom systems.     

Universality of multifragmentation of residual nuclei produced in high-energies nucleus-nucleus interactions

Experimental data on the multifragmentation of residual nuclei produced in the krypton interactions with photoemulsion nuclei at 0.9 GeV per projectile nucleon are presented and compared with similar data on fragmentation from experiments where gold nuclei of energy 10.7 GeV per nucleon appear as projectiles. It is shown for the first time that there exist two modes of nuclear multifragmentation, those where less (first mode) or more (second mode) than half of nucleons are knocked out of the incident nucleus. Residual nuclei that have close masses and which are produced in various reactions accompanied by the knock-on of more than half of nucleons of the initial nucleus fragment in nearly the same way. In addition, evidence for a radial flux of spectator fragments is obtained for the first time in the decay of residual nuclei of krypton projectiles.     

Analysis of variances of quasirapidities in collisions of gold nuclei with track-emulsion nuclei

A new method of an analysis of variances was developed for studying n-particle correlations of quasirapidities in nucleus-nucleus collisions for a large constant number n of particles. Formulas that generalize the results of the respective analysis to various values of n were derived. Calculations on the basis of simple models indicate that the method is applicable, at least for n ?? 100. Quasirapidity correlations statistically significant at a level of 36 standard deviations were discovered in collisions between gold nuclei and track-emulsion nuclei at an energy of 10.6 GeV per nucleon. The experimental data obtained in our present study are contrasted against the theory of nucleus-nucleus collisions.     

Nuclear correlations and the r process

We show that long-range correlations for nuclear masses have a significant effect on the synthesis of heavy elements by the r?process. As calculated by Delaroche et?al. [Phys. Rev. C 81, 014303 (2010)], these correlations suppress magic number effects associated with minor shells. This impacts the calculated abundances before the third r-process peak (at mass number A≈195), where the abundances are low and form a trough. This trough and the position of the third abundance peak are strongly affected by the masses of nuclei in the transition region between deformed and spherical. Based on different astrophysical environments, our results demonstrate that a microscopic theory of nuclear masses including correlations naturally smoothens the separation energies, thus reducing the trough and improving the agreement with observed solar system abundances.     

Nucleon momentum distribution of ~(56)Fe from the axially deformed relativistic mean-field model with nucleon-nucleon correlations

Nucleon momentum distribution(NMD), particularly its high-momentum components, is essential for understanding the nucleonnucleon(NN) correlations in nuclei. Herein, we develop the studies of NMD of ~(56)Fe from the axially deformed relativistic mean-field(RMF) model. Moreover, we introduce the effects of NN correlation into the RMF model from phenomenological models basing on deuteron and nuclear matter. For the region k k_F, the effects of deformation on the NMD of the RMF model are investigated using the total and single-particle NMDs. For the region k k_F, the high-momentum components of the RMF model are modified by the effects of NN correlation, which agree with the experimental data. Comparing the NMD of relativistic and non-relativistic mean-field models, the relativistic effects on nuclear structures in momentum space are analyzed. Finally, by analogizing the tensor correlations in deuteron and Jastrow-type correlations in nuclear matter, the behaviors and contributions of NN correlations in ~(56)Fe are further analyzed, which helps clarify the effects of the tensor force on the NMD of heavy nuclei.     

Nuclear Short range correlations in finite nuclei

The short-range correlations between nucleons in finite nuclei are investigated in the framework of Glauber multiple scattering theory without any free parameters. The effects on proton-nucleus and nucleus - nucleus interactions such as p - {4}He$ and {4}He- {12}C elastic scattering, and in particular the proton elastic scattering off hallo-like nuclei, {6,8}He, are estimated. Our calculations show that the short-range correlations play an important role in reproducing experimental data and could be also thought of as being the origin and nature of halo-like phenomena in the nuclear structure. More accurate calculations along this line are needed.     

Self-consistent description of <Emphasis Type="Italic">EL</Emphasis> transitions between one-phonon states in magic nuclei

Transition probabilities between low-lying one-phonon states of magic nuclei are for the first time computed self-consistently within an approach to anharmonic effects based on the quantum theory of many-body systems. In the adopted approach, three-quasiparticle correlations in the ground state are taken into account, and the nuclear mean field is interrelated with the effective nucleon–nucleon interaction. These quantities are derived using the energy density functional method with known parameters of the Fayans functional. The E1 and E2 transitions in the ¹³²Sn and ²⁰⁸Pb nuclei are considered as an example, and a reasonably good agreement with the data on these nuclei is reached. Three-quasiparticle correlations in the ground state are shown to make a significant contribution to the probabilities of the discussed transitions.     

A simple geometrical approach to particle production in collisions with nuclei

It is argued that hadron collisions with nuclei are similar to hadron-hadron collisions, having similar properties for the impact parameter distributions and the leading particle spectra. The relevant existing high-energy data, including the universality of multiplicity distributions and the possibility of geometrical scaling in reactions with nuclei, are easily understood in the framework of geometrical models by extending to p-nucleus collisions what was learnt about impact parameter and leading particles in pp collisions. The questions of forward-backward correlations and photo- and electroproduction are briefly discussed.