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.