arXiv subjects

Pawel Danielewicz

Publications and source records attributed to Pawel Danielewicz.

47 records · Page 3Linked to original sources

arXiv2006

Nuclear symmetry energy: from nuclear extremes to neutron-star matter

Extrapolations from nuclei to neutron stars hinge on the symmetry term in nuclear binding formulas. The term describes reduction in the binding associated with neutron-proton (np) imbalance. Regrettably, binding formulas in the literature commonly lack an intrinsic consistency with regard to the symmetry term. Our elementary considerations determine the universal macroscopic limit for the term and predict its weakening in light nuclei due to emergence of the nuclear asymmetry-skin. Experimental systematic of isobaric-analogue states allows for a determination of the volume and surface coefficients within the macroscopic limit of the symmetry term, disregarding any reminder of a binding formula. The results are next exploited to constrain the dependence of symmetry energy on nuclear density, essential for the neutron-star predictions.

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arXiv2005

Hadron production from resonance decay in relativistic collisions

A statistical model for decay and formation of heavy hadronic resonances is formulated. The resonance properties become increasingly uncertain with increasing resonance mass. Drawing on analogy with the situation in low-energy nuclear physics, we employ the Weisskopf approach to the resonance processes. In the large-mass limit, the density of resonance states in mass is governed by a universal Hagedorn-like temperature T_H. As resonances decay, progressively more and more numerous lighter states get populated. For T_H \simeq 170 MeV, the model describes data for the hadron yield ratios at the RHIC and SPS energies under the extreme assumption of a single heavy resonance giving rise to measured yields.

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arXiv2005

Probing the isospin dependence of the in-medium nucleon-nucleon cross sections with radioactive beams

Within a transport model we search for potential probes of the isospin dependence of the in-medium nucleon-nucleon (NN) cross sections. Traditional measures of the nuclear stopping power are found sensitive to the magnitude but they are ambiguous for determining the isospin dependence of the in-medium NN cross sections. It is shown that isospin tracers, such as the neutron/proton ratio of free nucleons, at backward rapidities/angles in nuclear reactions induced by radioactive beams in inverse kinematics is a sensitive probe of the isospin dependence of the in-medium NN cross sections. At forward rapidities/angles, on the other hand, they are more sensitive to the density dependence of the symmetry energy. Measurements of the rapidity/angular dependence of the isospin transport in nuclear reactions will enable a better understanding of the isospin dependence of in-medium nuclear effective interactions.

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arXiv2004

3D Imaging in Heavy-Ion Reactions

We report an extension of the source imaging method for imaging full three-dimensional sources from three-dimensional like-pair correlations. Our technique consists of expanding the correlation data and the underlying source function in spherical harmonics and inverting the resulting system of one-dimensional integral equations. With this method of attack, we can image the source function quickly, even with the extremely large data sets common in three-dimensional analyses. We apply our method to the recently measured E859 un-Coulomb corrected data.

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arXiv2000

Clocking hadronization in relativistic heavy ion collisions with balance functions

A novel state of matter has been hypothesized to exist during the early stage of relativistic heavy ion collisions, with normal hadrons not appearing until several fm/c after the start of the reaction. To test this hypothesis, correlations between charges and their associated anticharges are evaluated with the use of balance functions. It is shown that late-stage hadronization is characterized by tightly correlated charge/anticharge pairs when measured as a function of relative rapidity.

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arXiv1999

Implications of the unusual structure in the pp correlation from Pb+Pb collisions at 158 AGeV

The recent NA49 measurement of two-proton correlation function shows an interesting and unexpected structure at large relative momentum. Applying source imaging techniques to the measurement, we find an unusually steep drop-off in the two-proton source function. We show that the steep drop-off is due to the structure in the correlation and the drop-off cannot be explained using conventional correlation analysis. We suggest possible physics reasons for the unusual source function.

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arXiv1998

Partons in Phase Space

Within QED, we examine several issues related to constructing a parton-model-based QCD transport theory. We rewrite the QED analog of the parton model, the Weizsaecker-Williams Approximation, entirely in terms of phase-space quantities and we study the phase-space photon and electron densities created by a classical point charge. We find that the densities take a distinctive ``source-propagator'' form. This form does not arise in a conventional derivation of the semiclassical transport equations because of the overuse of the gradient approximation. We do not apply the gradient approximation and so derive the phase-space analog of the Generalized Fluctuation-Dissipation Theorem. Together, this theorem and the expression for the phase-space particle self-energies give a set of coupled phase-space evolution equations. We illustrate how these evolution equations can be used perturbatively or to derive semiclassical transport equations. Our work relies on phase-space propagators and sources, so we describe them in detail when calculating the photon and electron phase-space densities. We use these tools to discuss the shape of a nucleon's parton cloud.

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arXiv1997

Optimized Discretization of Sources Imaged in Heavy-Ion Reactions

We develop the new method of optimized discretization for imaging the relative source from two particle correlation functions. In this method, the source resolution depends on the relative particle separation and is adjusted to available data and their errors. We test the method by restoring assumed pp sources and then apply the method to pp and IMF data. In reactions below 100 MeV/nucleon, significant portions of the sources extend to large distances (r > 20 fm). The results from the imaging show the inadequacy of common Gaussian source-parametrizations. We establish a simple relation between the height of the pp correlation function and the source value at short distances, and between the height and the proton freeze-out phase-space density.

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arXiv1997

Imaging of Sources in Heavy-Ion Reactions

Imaging of sources from data within the intensity interferometry is discussed. In the two-pion case, the relative pion source function may be determined through the Fourier transformation of the correlation function. In the proton-proton case, the discretized source function may be fitted to the correlation data.

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arXiv1996

Non-equilibrium modifications of the nuclear equation of state

Non-equilibrium modifications of the nuclear equation of state are assessed in the framework of Extended Irreversible Thermodynamics. The expected size of the non-equilibrium corrections to quantities like the nuclear-matter incompressibility $K$ and the liquid-vapor critical temperature $T_c$ are compared to the uncertainties associated at present with the usual equilibrium values. The quantitative estimates are obtained in situations characterized by a stationary planar shear flow of realistic magnitude, or by a stationary temperature gradient.

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arXiv1995

Delays Associated with Elementary Processes in Nuclear Reaction Simulations

Scatterings, particularly those involving resonances, and other elementary processes do not happen instantaneously. In the context of semiclassical nuclear reaction simulations, we consider delays associated with an interaction for incident quantum wave-packets. As a consequence, we express delays associated with elementary processes in terms of elements of the scattering matrix and phase shifts for elastic scattering. We show that, to within the second order in density, the simulation must account for delays in scattering consistently with the mean field in order to properly model thermodynamic properties such as pressure and free-energy density. The delays associated with nucleon-nucleon and pion-nucleon scattering in free space are analysed with their nontrivial energy dependence. Finally, an example of s-channel scattering of massless partons is studied, and scattering schemes in nuclear reaction simulations are investigated in the context of scattering delays.

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