78 research outputs found
Spinodal amplification of density fluctuations in fluid-dynamical simulations of relativistic nuclear collisions
Extending a previously developed two-phase equation of state, we simulate
head-on relativistic lead-lead collisions with fluid dynamics, augmented with a
finite-range term, and study the effects of the phase structure on the
evolution of the baryon density. For collision energies that bring the bulk of
the system into the mechanically unstable spinodal region of the phase diagram,
the density irregularities are being amplified significantly. The resulting
density clumping may be exploited as a signal of the phase transition, possibly
through an enhanced production of composite particles.Comment: 4 pages 4 figures, version accepted by PR
Spinodal decomposition during the hadronization stage at RHIC?
The expansion of strongly interacting matter formed in high-energy nuclear
collisions drives the system through the region of phase coexistence. The
present study examines the associated spinodal instability and finds that the
degree of amplification may be sufficient to raise the prospect of using the
spinodal pattern formation as a diagnostic tool for probing the hadronization
phase transition.Comment: 4 pages, 4 eps figure
Phi-Meson production at RHIC, strong color fields and intrinsic transverse momenta
We investigate the effects of strong color fields and of the associated enhanced intrinsic transverse momenta on the phi-meson production in ultrarelativistic heavy ion collisions at RHIC. The observed consequences include a change of the spectral slopes, varying particle ratios, and also modified mean transverse momenta. In particular, the composition of the production processes of phi-mesons, that is, direct production vs. coalescence-like production, depends strongly on the strength of the color fields and intrinsic transverse momenta and thus represents a sensitive probe for their measurement
Signals of spinodal hadronization: strangeness trapping
If the deconfinement phase transformation of strongly interacting matter is
of first-order and the expanding chromodynamic matter created in a high-energy
nuclear collision enters the corresponding region of phase coexistence, a
spinodal phase separation might occur. The matter would then condense into a
number of separate blobs, each having a particular net strangeness that would
remain approximately conserved during the further evolution. We investigate the
effect that such `strangeness trapping' may have on strangeness-related
hadronic observables. The kaon multiplicity fluctuations are significantly
enhanced and thus provide a possible tool for probing the nature of the phase
transition experimentally.Comment: 15 pages, 11 eps figure
Quantitative analysis of the relation between entropy and nucleosynthesis in central Ca + Ca and Nb + Nb collisions
The final states of central Ca + Ca and Nb + Nb collisions at 400 and 1050 MeV/nucleon and at 400 and 650 MeV/nucleon, respectively, are studied with two independently developed statistical models, namely the classical microcanonical model and the quantum-statistical grand canonical model. It is shown that these models are in agreement with each other for these systems. Furthermore, it is demonstrated that there is essentially a one-to-one relationship between the observed relative abundances of the light fragments p, d, t, 3He, and α and the entropy per nucleon, for breakup temperatures greater than 30 MeV. Entropy values of 3.5–4 are deduced from high-multiplicity selected fragment yield data
Treatment of Pionic Modes at the Nuclear Surface for Transport Descriptions
Dispersion relations and amplitudes of collective pionic modes are derived in
a pi + nucleon-hole + delta-hole model for use in transport descriptions by
means of a local density approximation. It is discussed how pionic modes can be
converted to real particles when penetrating the nuclear surface and how
earlier treatments can be improved. When the surface is stationary only free
pions emerge. The time-dependent situation is also addressed, as is the
conversion of non-physical (i.e. unperturbed delta-hole) modes to real
particles when the nuclear density vanishes. A simplified one-dimensional
scenario is used to investigate the reflection and transmission of pionic modes
at the nuclear surface. It is found that reflection of pionic modes is rather
unlikely, but the process can be incorporated into transport descriptions by
the use of approximate local transmission coefficients.Comment: LaTeX 24 pages, 12 postscript figures in accompanying uuencoded fil
INCORPORATION OF QUANTUM STATISTICAL FEATURES IN MOLECULAR DYNAMICS
We formulate a method for incorporating quantum fluctuations into molecular-
dynamics simulations of many-body systems, such as those employed for energetic
nuclear collision processes. Based on Fermi's Golden Rule, we allow spontaneous
transitions to occur between the wave packets which are not energy eigenstates.
The ensuing diffusive evolution in the space of the wave packet parameters
exhibits appealing physical properties, including relaxation towards quantum-
statistical equilibrium.Comment: 8 latex pages + 1 uuencoded ps figur
Effects of Spin-Isospin Modes in Transport Simulations
In-medium properties derived for nuclear matter in a microscopic pi +
nucleon-hole + delta-hole model are incorporated into transport simulations of
nuclear collisions by means of a local-density approximation and by utilizing a
local medium frame. Certain features of the transport results differ from those
based on the corresponding vacuum properties. Comparisons of the pi and delta
production rates, as well as pion energy spectra, are discussed in particular.Comment: 11 pages total, Latex with psfig, and embedded 4 eps figure
Dynamical simulation of DCC formation in Bjorken rods
Using a semi-classical treatment of the linear sigma model, we simulate the
dynamical evolution of an initially hot cylindrical rod endowed with a
longitudinal Bjorken scaling expansion (a ``Bjorken rod''). The field equation
is propagated until full decoupling has occurred and the asymptotic many-body
state of free pions is then obtained by a suitable Fourier decomposition of the
field and a subsequent stochastic determination of the number of quanta in each
elementary mode. The resulting transverse pion spectrum exhibits visible
enhancements below 200 MeV due to the parametric amplification caused by the
oscillatory relaxation of the chiral order parameter. Ensembles of such final
states are subjected to various event-by-event analyses. The factorial moments
of the multiplicity distribution suggest that the soft pions are
non-statistical. Furthermore, their emission patterns exhibit azimuthal
correlations that have a bearing on the domain size in the source. Finally, the
distribution of the neutral pion fraction shows a significant broadening for
the soft pions which grows steadily as the number of azimuthal segments is
increased. All of these features are indicative of disoriented chiral
condensates and it may be interesting to apply similar analyses to actual data
from high-energy nuclear collision experiments.Comment: 38 pages total, incl 26 ps figures ([email protected]
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