Isospin Correlations Research Articles

Isospin Correlations in Isotope Yields at Intermediate and High Energy Heavy-Ion Collisions

Isospin Correlations in Isotope Yields at Intermediate and High Energy Heavy-Ion Collisions

Experimental studies of neutrino nuclear responses and nuclear structures for neutrino nuclear physics

Neutrino nuclear responses associated with astro neutrinos and double beta decays are crucial to extract neutrino properties of astro particle physics interests. The present report reviews briefly recent experimental studies of the neutrino nuclear responses. Single beta decays and electron captures, charge exchange nuclear reactions, muon and photon nuclear reactions, neutrino nuclear reactions and nucleon transfer reactions are used to study neutrino nuclear responses. Discussions are made on nucleonic and nonnucleonic spin isospin correlations and renormalization (quenching) effects on axial weak responses.

Universality of nucleon-nucleon short-range correlations: The factorization property of the nuclear wave function, the relative and center-of-mass momentum distributions, and the nuclear contacts

The two-nucleon momentum distributions have been calculated for nuclei up to A=40 and various values of the relative and center-of-mass momenta and angle between them. For complex nuclei a parameter-free linked-cluster expansion, based upon a realistic local two-nucleon interaction of the Argonne family and variational wave function featuring central, tensor, spin and iso-spin correlations, has been used. The obtained results show that: 1) independently of the mass number A, at values of the relative momentum k_rel> 2 fm^{-1} the proton-neutron momentum distributions for back-to-back (BB) nucleons (K_cm=0) exhibit the factorization property n_A^{pn}(k_rel,K_cm=0)=C_A^{pn} n_D(k_rel) n_{cm}^{pn}(K_cm=0), where n_D is the deuteron momentum distribution, n_{cm}^{pn}(K_{cm}=0) the momentum distribution of the c.m. motion of the pair and C_A^{pn} the nuclear contact measuring the number of BB pn pairs with deuteron-like momenta; 2) the values of the proton-neutron nuclear contact C_A^{pn} are obtained in a model-independent way from the ratio n_A^{pn}(k_rel,K_cm=0)/n_D(k_rel) n_{cm}^{pn}(K_cm=0); 3) also the K_cm-integrated pn momentum distributions divided by the deuteron momentum distribution exhibits a constant behavior equal to C_A^{pn}, but only at very high values of k_{rel}> 3.5fm^{-1}, where the relative momentum distribution is entirely governed by BB short-range correlated nucleons; 4) the absolute value of the number of pn and pp short-range correlated pairs is calculated, illustrating that the high values (K_cm>1 fm^{-1}) of the pair c.m. momentum appreciably reduce the dominance of the pn over pp pairs produced by the tensor force when K_cm=0; 5) calculations are in good agreement with the VMC calculations for light nuclei and with available experimental on the processes A(e,e'pn)X and A(e,e'pp)X.

GT neutrino–nuclear responses for double beta decays and astro neutrinos

Gamow–Teller nuclear matrix elements (NMEs) for pairs of ground-state-to-ground-state transitions, in particular their geometric mean NME , are studied. The observed means in the medium-heavy mass region are compared with the corresponding single-quasiparticle (qp) NMEs and the means calculated by the proton neutron qp random-phase approximation (pnQRPA). The NMEs turn out to be insensitive to the nucleon occupancy/vacancy amplitudes and to the particle–particle interaction parameter of the pnQRPA. The observed mean NMEs are found to be reduced by a coefficient relative to the effective qp NMEs and by a coefficient with respect to the pnQRPA NMEs. The reductions associated with the spin isospin correlations and nuclear medium effects, and their impact on nuclear double beta decays and astro-neutrino–nuclear interactions are discussed.

Isospin correlations in two-partite hexagonal optical lattices

Two-component mixtures in optical lattices reveal a rich variety of different phases. We employ an exact diagonalization method to obtain the relevant correlation functions in hexagonal optical lattices to characterize those phases. We relate the occupation difference of the two species to the magnetic polarization. `Iso'-magnetic correlations disclose the nature of the system, which can be of easy-axis type, bearing phase segregation, or of easy-plane type, corresponding to super-counter-fluidity. In the latter case, the correlations reveal easy-plane segregation, involving a highly-entangled state. We identify striking correlated supersolid phases appearing within the superfluid limit.

Spin-dipole nuclear matrix elements for double beta decays and astro-neutrinos

Spin-dipole (SD) nuclear matrix elements (NMEs) M±(SD2) for unique first forbidden β±2−→0+ ground-state-to-ground-state transitions are studied by using effective microscopic two-nucleon interactions in realistic single-particle model spaces. The observed values of the NMEs Mexp±(SD2) are compared with the values of the single-quasiparticle NMEs Mqp±(SD2) without nucleon spin–isospin (στ) correlation and the QRPA NMEs MQRPA±(SD2) with the στ correlation. The observed SD matrix elements are found to be reduced by the factor k≈0.2 with respect to Mqp±(SD2) and by the factor kNM≈0.5 with respect to MQRPA±(SD2). We then infer that the SD NME is reduced considerably partly by the nucleon στ correlations and partly by other non-nucleonic and nucleonic correlations which are not explicitly included in the QRPA. Impact of the found reduction factors on the magnitudes of the NMEs involved in neutrino-less double beta decays and astro-neutrino interactions are discussed.

Two-Dimensional Heisenberg Behavior ofJeff=1/2Isospins in the Paramagnetic State of the Spin-Orbital Mott InsulatorSr2IrO4

The dynamical correlations of J(eff)=1/2 isospins in the paramagnetic state of spin-orbital Mott insulator Sr2IrO4 were revealed by resonant magnetic x-ray diffuse scattering. We found a two-dimensional antiferromagnetic fluctuation with a large in-plane correlation length exceeding 100 lattice spacings at even 20 K above the magnetic ordering temperature. In marked contrast to the naive expectation of the strong magnetic anisotropy associated with an enhanced spin-orbit coupling, we discovered an isotropic isospin correlation that is well described by the two-dimensional S=1/2 quantum Heisenberg model. The estimated antiferromagnetic coupling constant as large as J∼0.1 eV that is comparable to the small Mott gap (<0.5 eV) points out the weak and marginal Mott character of this spin-orbital entangled system.

From multifragmentation to neck fragmentation: Mass, isospin, and velocity correlations

From multifragmentation to neck fragmentation: Mass, isospin, and velocity correlations

Density, spin, and isospin correlations in low-density two-component Fermi superfluid

Finding the distinct features of the crossover from the regime of large overlapping Cooper pairs to the limit of non-overlapping pairs of fermions (Shafroth pairs) in multi-component Fermi systems remains a topical problem in a quantum many-body theory. Here this transition is studied by calculating the two-body density, spin and isospin correlation functions in dilute two-component Fermi superfluid, taking as an example an infinite system of protons and neutrons (nuclear matter). It is shown that criterion of the crossover [Phys. Rev. Lett. 95, 090402 (2005)], formulated for ultracold fermionic atomic gases and consisting in the change of the sign of the density correlation function at low momentum transfer, fails to describe correctly the density-driven BEC–BCS transition at finite isospin asymmetry or finite temperature. As an unambiguous signature of the BEC–BCS transition, one can use the presence (BCS regime) or absence (BEC regime) of the singularity in the momentum distribution of the quasiparticle density of states.

Two-body correlation functions in dilute nuclear matter

Finding the distinct features of the crossover from the regime of large overlapping Cooper pairs to the limit of non-overlapping pairs of fermions (Shafroth pairs) in multicomponent Fermi systems remains one of the actual problems in a quantum many-body theory. Here this transition is studied by calculating the two-body density, spin and isospin correlation functions in dilute asymmetric nuclear matter. It is shown that criterion of the crossover (Phys. Rev. Lett. 95, 090402 (2005)), consisting in the change of the sign of the density correlation function at low momentum transfer, fails to describe correctly the density-driven BEC-BCS transition at finite isospin asymmetry or finite temperature. As an unambiguous signature of the BEC-BCS transition, there can be used the presence (BCS regime) or absence (BEC regime) of the singularity in the momentum distribution of the quasiparticle density of states.

Two-body correlation functions in nuclear matter with neutron-proton condensate

The density, spin, and isospin correlation functions in nuclear matter with a neutron-proton condensate are calculated to study the possible signatures of the BEC-BCS crossover in the low-density region. It is shown that the criterion of the crossover (Phys. Rev. Lett. 95, 090402 (2005)), consisting in the change of the sign of the density correlation function at low momentum transfer, fails to describe correctly the density-driven BEC-BCS transition at finite isospin asymmetry or finite temperature. The presence (BCS regime) or absence (BEC regime) of the singularity in the momentum distribution of the quasiparticle density of states can be used as an unambiguous signature of the BEC-BCS transition.

Resummation of angular dependent corrections in spontaneously broken gauge theories

Recent investigations of electroweak radiative corrections have revealed the importance of higher order contributions in high energy processes, where the size of typical corrections can exceed those associated with QCD considerably. Beyond one loop, only universal (angular independent) corrections are known to all orders except for massless $e^+ e^- \longrightarrow f {\overline f}$ processes where also angular dependent corrections exist in the literature. In this paper we present general arguments for the consistent resummation of angular dependent subleading (SL) logarithmic corrections to all orders in the regime where all invariants are still large compared to the gauge boson masses. We discuss soft isospin correlations, fermion mass and gauge boson mass gap effects, the longitudinal and Higgs boson sector as well as mixing contributions including CKM effects for massive quarks. Two loop arguments are interpreted in the context of the effective high energy effective theory based on the Standard Model Lagrangian in the symmetric basis with the appropriate matching conditions to include the soft QED regime. The result is expressed in exponentiated operator form in a CKM-extended isospin space in the symmetric basis. Thus, a full electroweak SL treatment based on the infrared evolution equation method is formulated for arbitrary high energy processes at future colliders. Comparisons with known results are presented.

Isospin asymmetry in the pseudospin dynamical symmetry.

Pseudospin symmetry in nuclei is investigated considering the Dirac equation with a Lorentz structured Woods-Saxon potential. The isospin correlation of the energy splittings of pseudospin partners with the nuclear potential parameters is studied. We show that, in an isotopic chain, the pseudospin symmetry is better realized for neutrons than for protons. This behavior comes from balance effects among the central nuclear potential parameters. In general, we found an isospin asymmetry of the nuclear pseudospin interaction, opposed to the nuclear spin-orbit interaction which is quasi-isospin symmetric.

Effects of strong and electromagnetic correlations on neutrino interactions in dense matter

An extensive study of the effects of correlations on both charged and neutral current weak interaction rates in dense matter is performed. Both strong and electromagnetic correlations are considered. The propagation of particle-hole interactions in the medium plays an important role in determining the neutrino mean free paths. The effects due to Pauli blocking and density, spin, and isospin correlations in the medium significantly reduce the neutrino cross sections. As a result of the lack of experimental information at high density, these correlations are necessarily model dependent. For example, spin correlations in nonrelativistic models are found to lead to larger suppressions of neutrino cross sections compared to those of relativistic models. This is due to the tendency of the nonrelativistic models to develop spin instabilities. Notwithstanding the above caveats, and the differences between nonrelativistic and relativistic approaches such as the spin- and isospin-dependent interactions and the nucleon effective masses, suppressions of order 2--3, relative to the case in which correlations are ignored, are obtained. Neutrino interactions in dense matter are especially important for supernova and early neutron star evolution calculations. The effects of correlations for protoneutron star evolution are calculated. Large effects on the internal thermodynamic properties of protoneutron stars, such as the temperature, are found. These translate into significant early enhancements in the emitted neutrino energies and fluxes, especially after a few seconds. At late times, beyond about 10 s, the emitted neutrino fluxes decrease more rapidly compared to simulations without the effects of correlations, due to the more rapid onset of neutrino transparency in the protoneutron star.

Many-body effects in 16O(e,e'p).

Effects of nucleon-nucleon correlations on exclusive (e,e'p) reactions on closed-shell nuclei leading to single-hole states are studied using $^{16}\mathrm{O}$(e, e'p${)}^{15}$N (6.32 MeV, 3/${2}^{\mathrm{\ensuremath{-}}}$) as an example. The quasihole wave function, calculated from the overlap of translationally invariant many-body variational wave functions containing realistic spatial, spin, and isospin correlations, seems to describe the initial state of the struck proton accurately inside the nucleus; however, it is too large at the surface. The effect of short-range correlations on the final state is found to be largely cancelled by the increase in the transparency for the struck proton. It is estimated that the values of the spectroscopic factors obtained wth the distorted wave impulse approximation may increase by a few percent due to correlation effects in the final state.

Disoriented chiral condensates and quantum mechanical isospin correlation

Classical considerationss suggest that the probability distribution P( R), where R is the ratio of neutral pions to total pions emitted from a disoriented chiral condensate (which has been hypothesized to form in heavy ion reactions) is R −1 2 2 . Quantum mechanical isospin correlations between the condensate and the remainder of the system can alter this. Moments of the P( R) distribution can be expressed in term of expectation values of ( I 2 N 2 ) m where I is the isospin carried by the condensate, N is the number of pions emitted and m is an arbitrary integer. We find that the probability distribution is very similar to the classical distribution for 0.1< R<0.9 unless the isospin carried by the condensate is very large.

Pion condensation in relativistic heavy ion collisions

Recently it was pointed out that coherent or condensated states of pions may account for the explanation of the Centauro events observed in cosmic ray showers. We argue that an occurence of condensed pions requires that the system evolves far out of thermal equilibrium. Besides an unusual charge ratio distribution we show that such a produced state also would lead to strong isospin correlations.

Electron-scattering studies of correlations in nuclei

The authors review theoretical estimates of spatial, spin, and isospin correlations among the nucleons in nuclei. The momentum distribution and spectral function of nucleons in nuclei are also discussed. The theoretical estimates are compared with the observed correlation effects in the inclusive scattering of electrons from nuclei, at energies ranging from a few hundred MeV to several GeV. The observed transparencies of nuclei to protons ejected in inclusive [ital e],[ital e][prime][ital p] reactions are also compared with their theoretical estimates. Finally, the quenching of exclusive single-quasiparticle-type reactions, indicative of the overall strength of correlations in nuclei, is discussed. There appears to be a qualitative agreement between theory and experiment, but a firm quantitative understanding is still to be obtained.

DISORIENTED CHIRAL CONDENSATE IN (1+1) LORENTZ-INVARIANT GEOMETRY

We consider isospin correlations of pions produced in a relativistic nuclear collision, using an effective theory of the chiral order parameter. Our theory has (1+1) Lorentz invariance as appropriate for the central rapidity region. We argue that in certain regions of space correlations of the chiral order parameter are described by the fixed point of the (1+1) WZNW model. The corresponding anomalous dimension determines scaling of the probability to observe a correlated cluster of pions with the size of this cluster in rapidity. Though the maximal size of clusters for which this scaling is applicable is cutoff by pion mass, such clusters can still include sufficiently many particles to make the scaling observable.

Correlation between neutrons and protons in heavy ion collisions

Generalized relationships between the variances of isobaric and isotopic distributions and the inclusive charge and mass distributions are deduced for isospin correlated statistical reaction processes in heavy ion collisions. We further deduce a general relation between the ratio of the inclusive mass to charge variances and the isospin correlation coefficient. In the context of the nucleon exchange model, the theoretical predictions agree with the experimental data in most of the cases.