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Scott Pratt

Publications and source records attributed to Scott Pratt.

At least 73 records · Page 4Linked to original sources
arXiv2007

Interpreting scattering wave functions in the presence of energy-dependent interactions

In scattering theory, the squared relative wave function $|ϕ({\bf q},{\bf r})|^2$ is often interpreted as a weight, due to final-state interactions, describing the probability enhancement for emission with asymptotic relative momentum $q$. An equivalence relation also links the integral of the squared wave function over all coordinate space to the density of states. This relation, which plays an important role in understanding two-particle correlation phenomenology, is altered for the case where the potential is energy dependent, as is assumed in various forms of reaction theory. Here, the modification to the equivalence relation is derived, and it is shown that the squared wave function should be augmented by a additional factor if it is to represent the emission enhancement for final-state interactions. Examples with relativistic vector interactions, e.g., the Coulomb interaction, are presented.

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arXiv2007

Status and Promise of Particle Interferometry in Heavy-Ion Collisions

After five years of running at RHIC, and on the eve of the LHC heavy-ion program, we highlight the status of femtoscopic measurements. We emphasize the role interferometry plays in addressing fundamental questions about the state of matter created in such collisions, and present an enumerated list of measurements, analyses and calculations that are needed to advance the field in the coming years.

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arXiv2007

Analyzing Correlation Functions with Tesseral and Cartesian Spherical Harmonics

The dependence of inter-particle correlations on the orientation of particle relative-momentum can yield unique information on the space-time features of emission in reactions with multiparticle final states. In the present paper, the benefits of a representation and analysis of the three-dimensional correlation information in terms of surface spherical harmonics is presented. The harmonics include the standard complex tesseral harmonics and the real cartesian harmonics. Mathematical properties of the lesser-known cartesian harmonics are illuminated. The physical content of different angular harmonic components in a correlation is described. The resolving power of different final-state effects with regarding to determining angular features of emission regions is investigated. The considered final-state effects include identity interference and strong and Coulomb interactions. The correlation analysis in terms of spherical harmonics is illustrated with the cases of gaussian and blast-wave sources for proton-charged meson and baryon-baryon pairs.

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arXiv2006

A Co-moving Coordinate System for Relativistic Hydrodynamics

The equations of relativistic hydrodynamics are transformed so that steps forward in time preserves local simultaneity. In these variables, the space-time coordinates of neighboring points on the mesh are simultaneous according to co-moving observers. Aside from the time step varying as a function of the location on the mesh, the local velocity gradient and the local density then evolve according to non-relativistic equations of motion. Analytic solutions are found for two one-dimensional cases with constant speed of sound. One solution has a Gaussian density profile when mapped into the new coordinates. That solution is analyzed for the effects of longitudinal acceleration in relativistic heavy ion collisions at RHIC, especially in regards to two-particle correlation measurements of the longitudinal size.

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arXiv2006

Shapes and Sizes from Non-Identical-Particle Correlations

I review the prospects for measuring source characteristics from correlations other than those involving identical pions. Correlations generated from Coulomb and strong interactions are shown to provide remarkable resolving power for determining three-dimensional information, in some cases accessing more detail than can be represented by Gaussian fits.

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arXiv2006

Origins of Bulk Viscosity at RHIC

A variety of physical phenomena can lead to viscous effects. Several sources of shear and bulk viscosity are reviewed with an emphasis on the bulk viscosity associated with chiral restoration and with chemical non-equilibrium. We show that in a mean-field treatment of the limiting case of a second order phase transition, the bulk viscosity peaks in a singularity at the critical point.

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arXiv2006

Viscosity at RHIC

A variety of physical phenomena can lead to viscous effects. In this talk we review several sources of shear and bulk viscosity with an emphasis on the bulk viscosity associated with chiral restoration. We show that in the limit of a second order phase transition, the viscosity peaks in a singularity at the critical point.

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arXiv2005

The nuclear matter phase diagram, multifragmentation, Zipf's law

Some of the progress in determining the phase boundaries of the nuclear phase diagram, the location of the critical point of the nuclear fragmentation phase transition, and the values of the critical exponents of this transition is reviewed. The recently postulated connection of the size of the largest fragments as a function of their rank with Zipf's law known from linguistics is discussed, and an exact formula is derived. We show that Zipf's law is not strictly observed in nuclear fragmentation, but that one can derive useful approximations.

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arXiv2005

Refractive Distortions of Two-Particle Correlations

Using optical model calculations it has recently been shown that refractive phenomena from the collective mean field can significantly alter the sizes inferred from two-pion correlations. We demonstrate that such effects can be accounted for in classical calculations if mean field effects are included.

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arXiv2005

Is HBT really puzzling?

Two-particle correlations from RHIC have provided a surprising snapshot of the final state at RHIC. In this talk I discuss the nature of the HBT puzzle and attempt to delineate several factors which might ultimately resolve the issue.

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arXiv2005

Zipf's Law and the Universality Class of the Fragmentation Phase Transition

We show that Zipf's Law for the largest clusters is not valid in an exact sense at the critical point of the fragmentation phase transition, contrary to previous claims. Instead, the extracted distributions of the largest clusters reflects the choice of universality class through the value of the critical exponent tau.

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arXiv2005

Correlation Functions: Getting into Shape

The ability to measure characteristics of source shapes using non-identical particle correlations is discussed. Both strong-interaction induced and Coulomb induced correlations are shown to provide sensitivity to source shapes. By decomposing correlation functions with spherical or Cartesian harmonics, details of the shapes can be especially well isolated.

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arXiv2005

Femtoscopy in Relativistic Heavy Ion Collisions: Two Decades of Progress

Analyses of two-particle correlations have provided the chief means for determining spatio-temporal characteristics of relativistic heavy ion collisions. We discuss the theoretical formalism behind these studies and the experimental methods used in carrying them out. Recent results from RHIC are put into context in a systematic review of correlation measurements performed over the past two decades. The current understanding of these results is discussed in terms of model comparisons and overall trends.

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arXiv2005

Refractive Distortions of Two-Particle Correlations from Classical Trajectory Calculations

Calculations of two-particle correlations usually assume particles interact only pair-wise after their final collisions with third bodies. By considering classical trajectories, we show that interactions with the mean field can alter the spatial dimensions of the outgoing phase-space-density profiles by tens of percent, consistent with more complicated quantum complications.

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arXiv2004

Quark recombination and elliptic flow

Elliptic flow systematics for different hadron species have been explained by quark coalescence models. It has been argued that the elliptic asymmetry v_2 should scale with the number of quarks that comprise the hadron. We show how these arguments are sensitive to the relative role of asymmetries in the phase space density vs. asymmetries in the effective volume of emission. We also discuss the degree to which coalescence arguments differ from thermal models. Illustrative calculations based on solving the Boltzmann equation are presented along with the results of blast-wave models. Although the issue is complicated, ambiguities might be clarified by measurements of source-size parameters for nucleons at higher transverse momenta.

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arXiv2003

Entropy Production at RHIC

For central heavy ion collisions at the RHIC energy, the entropy per unit rapidity dS/dy at freeze-out is extracted with minimal model dependence from available experimental measurements of particle yields, spectra, and source sizes estimated from two-particle interferometry. The extracted entropy rapidity density is consistent with lattice gauge theory results for a thermalized quark-gluon plasma with an energy density estimated from transverse energy production at RHIC.

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arXiv2003

Thermal production of the $ρ$ meson in the $π^+π^-$ channel

Recent measurements of the pi^+pi^- invariant mass distribution at RHIC show a shifted peak for the rho meson in 100A GeV in peripheral Au + Au and even in p + p collisions. A recent theoretical study based on a picture of in-medium production rates of pions, showed that a large shift could result from a combination of the Boltzmann factor and the collisional broadening of the rho. Here we argue that the two-pion density of states is the appropriate quantity if one assumes a sudden break-up of the system. Methods for calculating the density of states which include Bose effects are derived. The resulting invariant mass distributions are significantly enhanced at lower masses and the rho peak is shifted downward by ~ 35 MeV.

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