Role Of Short-range Correlations Research Articles

Study of multinucleon knockout reactions of exotic nuclei in the region of Sn

The experimental data collected during the S515 experiment performed by the R3B collaboration at GSI/FAIR represent a great opportunity to investigate nucleon knockout reactions of exotic nuclei in the region of Sn using complete kinematics measurements. These cross sections can be used in the future to investigate the quenching in the knockout of the minority species (neutrons or protons) in nuclei far from stability. Some of the arguments put forward are the underestimation of the knockout of deeply bound nucleons, final state interactions or the role of short-range correlations (SRC). Recently, several works based on inclusive measurements have shown that these SRCs could reduce the single nucleon knockout cross sections by around 50%, depending on the neutron excess (N/Z) of the initial projectile. The S515 data can help us to go further in this investigation because it allows to correlate the knockout cross sections of one, two or more nucleons with the number of protons and neutrons emitted from the target and which can be detected by the CALIFA and NeuLAND detectors, respectively, and perform complete kinematical studies on the nature of the event (SRC, evaporation, emission of clusters, final-state interactions...). Here the results obtained for the charge distribution of reaction residues are presented, which is one of the first steps of the still on-going analysis.

Green's Function Techniques for Infinite Nuclear Systems

I review the application of self-consistent Green's functions methods to study the properties of infinite nuclear systems. Improvements over the last decade, including the consistent treatment of three-nucleon forces and the development of extrapolation methods from finite to zero temperature, have allowed for realistic predictions of the equation of state of infinite symmetric, asymmetric and neutron matter based on chiral interactions. Microscopic properties, like momentum distributions or spectral functions, are also accessible. Using an indicative set of results based on a subset of chiral interactions, I summarise here the first-principles description of infinite nuclear system provided by Green's functions techniques, in the context of several issues of relevance for nuclear theory including, but not limited to, the role of short-range correlations in nuclear systems, nuclear phase transitions and the isospin dependence of nuclear observables.

A systematic study of the effect of short range correlations on the occupation numbers of the shell model orbits in light nuclei

The role of short-range correlations on the depletion of the Fermi sea is studied in light nuclei.The short range correlations are considered in an approximate treatment allowing a systematic study of nuclei in the region 4 < A < 40. The "natural orbital" representation is used for the determination of the occupation probabilities of the shell model orbits of the ground state wave function. The depletion of the nuclear Fermi sea appears to be, on the average, about 32%.

Scale dependence of deuteron electrodisintegration

A model calculation of deuteron electrodisintegration is used to explore renormalization group (RG) scale dependence for knock-out reactions. When evolved to different resolutions with the similarity RG (SRG), the initial deuteron wave function, the current operator, and the final state interactions (FSI) are all modified, but how they combine depends strongly on the kinematic region. In some regions, for example, the FSI are largely unaffected by evolution, while elsewhere FSI are greatly reduced. For certain kinematics, the impulse approximation at a high RG resolution gives an intuitive picture in terms of a one-body current breaking up a short-range correlated neutron-proton pair, although FSI distort this simple picture. With evolution to low resolution, however, the cross section is unchanged but a very different and arguably simpler intuitive picture emerges, with the evolved current efficiently represented at low momentum through derivative expansions or low-rank singular value decompositions. A consequence is that intuition about physics such as the role of short-range correlations or $D$-state mixing in particular kinematic regimes can be strongly scale dependent.

EXPECTATION OF FORWARD–BACKWARD RAPIDITY CORRELATIONS IN p+p COLLISIONS AT THE LHC ENERGIES

Forward–backward correlation strength (b) as a function of pseudorapidity intervals for experimental data from [Formula: see text] nonsingly diffractive collisions are compared to PYTHIA and PHOJET model calculations. The correlations are discussed as a function of rapidity window (Δη) symmetric about the central rapidity as well as rapidity window separated by a gap (η gap ) between forward and backward regions. While the correlations are observed to be independent of Δη, it is found to decrease with increase in η gap . This reflects the role of short range correlations and justifies the use of η gap to obtain the accurate information about the physics of interest, the long range correlations. The correlation strength from PYTHIA are in agreement with the available experimental data while those from the PHOJET give higher values. For p+p collisions at [Formula: see text], 10 and 14 TeV, the correlation strength from PHOJET are lower compared to those from PYTHIA, this is in contrast to the observations at lower energies. The experimental b value shows a linear dependence on [Formula: see text] with the maximum value of unity being reached at [Formula: see text], beyond the top LHC energy. However calculations from the PYTHIA and PHOJET models indicate a deviation from linear dependence on [Formula: see text] and saturation in the b values being reached beyond [Formula: see text]. Such a saturation in correlation values could have interesting physical interpretations related to clan structures in particle production. Strong forward–backward correlations are associated with cluster production in the collisions. The average number of charged particles to which the clusters fragments, called the cluster size, are found to also increase linearly with [Formula: see text] for both data and the models studied. The rate of increase in cluster size versus [Formula: see text] from models studied are larger compared to those from the data and higher for PHOJET compared to PYTHIA. Our study indicates that the forward–backward measurements will provide a clear distinguishing observable for the models studied at LHC energies.

Thermodynamics and Energy Spectrum of Strongly Correlated Proton and Ionic Conductors

We describe proton and ionic conductors with lattice models. For proton conductors with hydrogen bonds we use the orientational-tunneling model that takes into account the proton transfer in the spirit of two-stage Grotthuss mechanism as well as the short-range interaction between protons. When simplified this model is reduced to the well-known spinless fermion model. In our investigation we focus on the role of short-range correlations between protons (ions) that may affect the behaviour of the system considerably. In frames of the projected coherent potential approximation we calculate the energy spectrum of the system in one-dimensional case. It consists of one or several energy bands depending on correlation strength. At half filling the system is in the insulating state when correlations are strong and is in the quasi-metallic state when correlations are weak. At certain range of parameters values we also observe the insulator-metal-like transition in the spectrum as it closes the gap with the temperature increase while the system exits in the charge-ordered state. This fact can be considered as theoretical explanation of superionic transition, i.e. transition from the low-temperature ordered (ferroelastic) state to high temperature conducting state with random distribution of ions (protons). We test the results with numerical calculations on finite clusters using exact diagonalization technique.

Short-range correlations in quark matter

We investigate the role of short-range correlations in quark matter within the framework of the SU(2) Nambu-Jona-Lasinio model. Employing a next-to-leading order expansion in 1/N{sub c} for the quark self-energy, we construct a fully self-consistent model that is based on the relations between spectral functions and self-energies. In contrast to the usual quasiparticle approximations, we take the collisional broadening of the quark spectral function consistently into account. Mesons are dynamically generated in the fashion of a random phase approximation, using full in-medium propagators in the quark loops. The results are self-consistently fed back into the quark self-energy. Calculations have been performed for finite chemical potentials at zero temperature. The short-range correlations not only generate finite widths in the spectral functions but also have influence on the chiral phase transition.

Vijay Pandharipande: Correlations in many-body systems

We discuss some of the aspects of V.R. Pandharipande's work, related mainly to the role of short-range correlations in nuclei and the understanding of quasi-elastic lepton scattering from nuclei and nucleons.

Molecular light scattering of multiplicity 1.5

The “interference” contributions from compact groups of scattering centers to the total intensity of molecular scattering in a liquid are analyzed. The result of the algebra of fluctuating quantities has been restored for the case of long-range correlations between the groups. The role of short-range correlations is most significant for moderate deviations (10−3−10−2) of the dimensionless temperature from its critical value. Estimates of the relative value and temperature peculiarities of the contributions of multiplicity 1.5 proportional to the third-order moment of the density fluctuations and an analysis of experimental data indicate that they can be partially observed under conditions deviating from the critical isochore.

Effects of short-range correlations on Ca isotopes.

The effect of Short Range Correlations (SRC) on Ca isotopes is studied using a simple phenomenological model. Theoretical expressions for the charge (proton) form factors, densities and moments of Ca nuclei are derived. The role of SRC in reproducing the empirical data for the charge density differences is examined. Their influence on the depletion of the nuclear Fermi surface is studied and the fractional occupation probabilities of the shell model orbits of Ca nuclei are calculated. The variation of SRC as function of the mass number is also discussed.

Short range correlations and fractional occupation probabilities.

The results of a recent study about the role of short-range correlations on the occupation numbers of the shell model orbits in light nuclei are reconsidered by assuming a sort of state dependence of the single particle wave functions in the ``natural orbital'' representation, which is used for the determination of the occupation probabilities. It turns out that such a treatment leads to a significant reduction of the total depletion of the nuclear Fermi sea. The state dependence of short-range correlations is also discussed.

Systematic study of the effect of short range correlations on the occupation numbers of the shell model orbits in light nuclei.

The role of short range correlations on the depletion of the Fermi sea is studied in light nuclei. The short range correlations are considered in an approximate treatment allowing a systematic study of nuclei in the region 4{le}{ital A}{le}40. The natural orbital'' representation is used for the determination of the occupation probabilities of the shell model orbits of the ground-state wave function. The depletion of the nuclear Fermi sea appears to be, on the average, about 32%.

Delta component in the nuclear ground state.

The \ensuremath{\Delta} component in the nuclear ground state is evaluated in connection with the \ensuremath{\Delta} dynamics. The various microscopic processes which could originate such components are separately studied. The role of short-range correlations is emphasized, as well as that of random-phase-approximation corrections. It is shown moreover that a rather large number of \ensuremath{\Delta}'s in a nucleus does not lead to contradictions with the standard shell model.

The magnetic form factors of 3He and 3H with mesonic-exchange corrections : Effects of the D-state and the role of short-range correlations

We show that the D-state of the trinucleon and the short-range behavior of the S- and D-state wave functions are extremely important in determining the magnetic form factors of the three-body system. We present a complete calculation of the form factors taking into account the conventional impulse approximation for the nuclear current and contributions from mesonic exchange currents. The D-state wave function has been determined by perturbation theory.

The role of short-range correlations in the nuclear photoeffect

The role of short-range correlations in the nuclear photoeffect

Short-Range Correlations and the Three-Body Binding Energy

The separable-potential approach of Mitra is extended by introducing an additional interaction which yields two-nucleon $S$-wave phase shifts to 340 MeV. A calculation of the exact binding energy and wave function of a simplified three-body system is used to determine the role of short-range correlations and the associated off-energy-shell matrix elements of the interaction. We find that the three-body binding energy ranges from 9.33 to 8.40 MeV; the larger value is calculated using a two-body interaction fitting low-energy data only, while the smaller value results from including a hard-shell repulsion. A smooth repulsion, which is equivalent to the hard shell in the two-body problem, yields a three-body binding energy of 8.79 MeV.