258 research outputs found
Why a long-lived fireball can be compatible with HBT measurements
The common interpretation of HBT data measured at top SPS energies leads to
apparent source lifetimes of 6-8 fm/c and emission duration of approximately
2-3 fm/c. We investigate a scenario with continuous pion emission from a
long-lived (~17 fm/c) thermalized source in order to show that it is not
excluded by the data. Starting from a description of the source's spacetime
expansion based on gross thermodynamical properties of hot matter (which is
able to describe a number of experimental observables), we introduce the pion
emission function with a contribution from continuous emission during the
source's lifetime and another contribution from the final breakup and proceed
by calculating the HBT parameters R_out and R_side. The results are compared
with experimental data measured at SPS for 158 AGeV central Pb-Pb collisions.
We achieve agreement with data, provided that some minor modifications of the
fireball evolution scenario are made and find that the parameter R_out is not
sensitive to the fireball lifetime, but only to the duration of the final
breakup, in spite of the fact that emission takes place throughout the whole
lifetime. We explicitly demonstrate that those findings do not alter previous
results obtained within this model.Comment: 13 pages, 5 figures, submitted to Phys. Rev. C. (revised description
of fireball expansion
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.Comment: 32 pages 10 figure
A model for the spacetime evolution of heavy-ion collisions at RHIC
We investigate the space-time evolution of ultrarelativistic Au-Au collisions
at full RHIC energy using a schematic model of the expansion. Assuming a
thermally equilibrated system, we can adjust the essential scale parameters of
this model such that the measured transverse momentum spectra and Hanbury-Brown
Twiss (HBT) correlation parameters are well described. We find that the
experimental data strongly constrain the dynamics of the evolution of the
emission source although hadronic observables for the most part reflect the
final breakup of the system.Comment: 9 pages, 3 figures, submitted to Phys. Rev.
Measures Of International Transport Cost For OECD Countries
This paper presents new estimates of country-specific international transport costs for 21 OECD countries over the period 1973-2005. The methodology is based on direct measures of air, maritime, and road transport costs rather than on cif/fob ratios or other balance of payments data employed in previous studies. Transport costs are calculated as costs per kilogramme for each mode of transport at a bilateral level and then aggregated. Australia and New Zealand are found to have the highest transport costs among the OECD countries considered, followed by Japan. The time trends are sensitive to the choice of deflator, but the results do not show an overall downward trend in transport costs for OECD countries, contrary to conventional wisdom, but consistent with Hummels’ (2007) recent study of global transport costs
Photonic measurements of the longitudinal expansion dynamics in Heavy-Ion collisions
Due to the smallness of the electromagnetic coupling, photons escape from the
hot and dense matter created in an heavy-ion collision at all times, in
contrast to hadrons which are predominantly emitted in the final freeze-out
phase of the evolving system. Thus, the thermal photon yield carries an imprint
from the early evolution. We suggest how this fact can be used to gain
information about where between the two limiting cases of Bjorken
(boost-invariant expansion) and Landau (complete initial stopping and
re-expansion) hydrodynamics the actual evolution can be found. We argue that
both the rapidity dependence of the photon yield and photonic HBT radii are
capable of answering this question.Comment: 10 pages, 3 figure
Yano-Koonin-Podgoretskii Parametrisation of the Hanbury Brown-Twiss Correlator
The Yano-Koonin-Podgoretskii (YKP) parametrisation of Hanbury Brown-Twiss
(HBT) two-particle correlation functions opens new strategies for extracting
the emission duration and testing the longitudinal expansion in heavy-ion
collisions. Based on the recently derived model-independent expressions, we
present a detailed parameter study of the YKP parameters for a finite,
hydrodynamically expanding source model of heavy-ion collisions. For the class
of models studied here, we show that the three YKP radius parameters have an
interpretation as longitudinal extension, transverse extension and emission
duration of the source in the YKP frame. This frame is specified by the fourth
fit parameter, the Yano-Koonin velocity which describes to a good approximation
the velocity of the fluid element with highest emissivity and allows to test
for the longitudinal expansion of the source. Deviations from this
interpretation of the YKP parameters are discussed quantitatively.Comment: 38 pages, REVTeX, 11 PS-figures, to be published in Z.Phys.
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