714 research outputs found

    Hadron production in relativistic nuclear collisions: thermal hadron source or hadronizing quark-gluon plasma?

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    Measured hadron yields from relativistic nuclear collisions can be equally well understood in two physically distinct models, namely a static thermal hadronic source vs.~a time-dependent, nonequilibrium hadronization off a quark-gluon plasma droplet. Due to the time-dependent particle evaporation off the hadronic surface in the latter approach the hadron ratios change (by factors of <5<\approx 5) in time. Final particle yields reflect time averages over the actual thermodynamic properties of the system at a certain stage of the evolution. Calculated hadron, strangelet and (anti-)cluster yields as well as freeze-out times are presented for different systems. Due to strangeness distillation the system moves rapidly out of the T, μq\mu_q plane into the μs\mu_s-sector. Strangeness to baryon ratios f_s=1-2 prevail during a considerable fraction (50%) of the time evolution (i.e. Λ\Lambda-droplets or even Ξ\Xi^--droplets form the system at the late stage: The possibility of observing this time evolution via HBT correlations is discussed). The observed hadron ratios require Tc160MeVT_c\approx 160 MeV and B1/4>200MeVB^{1/4}>\approx 200 MeV. If the present model is fit to the extrapolated hadron yields, metastable hypermatter can only be produced with a probability p<108p< 10^{-8} for A4A \ge 4.Comment: Submitted to Z. Phys.

    Parity Doublet Model applied to Neutron Stars

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    The Parity doublet model containing the SU(2) multiplets including the baryons identified as the chiral partners of the nucleons is applied for neutron star matter. The chiral restoration is analyzed and the maximum mass of the star is calculated.Comment: Proceeding to the conference International Symposium on Exotic States of Nuclear Matte

    Fast Dynamical Evolution of Hadron Resonance Gas via Hagedorn States

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    Hagedorn states are the key to understand how all hadrons observed in high energy heavy ion collisions seem to reach thermal equilibrium so quickly. An assembly of Hagedorn states is formed in elementary hadronic or heavy ion collisions at hadronization. Microscopic simulations within the transport model UrQMD allow to study the time evolution of such a pure non-equilibrated Hagedorn state gas towards a thermally equilibrated Hadron Resonance Gas by using dynamics, which unlike strings, fully respect detailed balance. Propagation, repopulation, rescatterings and decays of Hagedorn states provide the yields of all hadrons up to a mass of m=2.5 GeV. Ratios of feed down corrected hadron multiplicities are compared to corresponding experimental data from the ALICE collaboration at LHC. The quick thermalization within t=1-2 fm\c of the emerging Hadron Resonance Gas exposes Hagedorn states as a tool to understand hadronization.Comment: 5 pages, 7 figures, 1 tabl

    In-medium properties of D-mesons at FAIR

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    We obtain the D-meson spectral density at finite temperature for the conditions of density and temperature expected at FAIR. We perform a self-consistent coupled-channel calculation taking, as a bare interaction, a separable potential model. The Λc\Lambda_c (2593) resonance is generated dynamically. We observe that the D-meson spectral density develops a sizeable width while the quasiparticle peak stays close to the free position. The consequences for the D-meson production at FAIR are discussed.Comment: 4 pages, 3 figures, to appear in the proceedings of 9th International Conference on Hypernuclear and Strange Particle Physics (HYP2006), Mainz (Germany), 10-14 October 200

    Covariant Canonical Gauge theory of Gravitation resolves the Cosmological Constant Problem

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    The covariant canonical transformation theory applied to the relativistic theory of classical matter fields in dynamic space-time yields a new (first order) gauge field theory of gravitation. The emerging field equations embrace a quadratic Riemann curvature term added to Einstein's linear equation. The quadratic term facilitates a momentum field which generates a dynamic response of space-time to its deformations relative to de Sitter geometry, and adds a term proportional to the Planck mass squared to the cosmological constant. The proportionality factor is given by a dimensionless parameter governing the strength of the quadratic term. In consequence, Dark Energy emerges as a balanced mix of three contributions, (A)dS curvature plus the residual vacuum energy of space-time and matter. The Cosmological Constant Problem of the Einstein-Hilbert theory is resolved as the curvature contribution relieves the rigid relation between the cosmological constant and the vacuum energy density of matter

    New Physics at the International Facility for Antiproton and Ion Research (FAIR) Next to GSI

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    The project of the international Facility for Antiproton and Ion Research (FAIR), co-located to the GSI facility in Darmstadt, has been officially started on November 7, 2007. The current plans of the facility and the planned research program will be described. An investment of about 1 billion euro will permit new physics programs in the areas of low and medium energy antiproton research, heavy ion physics complementary to LHC, as well as in nuclear structure and astrophysics. The facility will comprise about a dozen accelerators and storage rings, which will enable simultaneous operations of up to four different beams.Comment: 7 pages, 1 figure. Invited Talk presented at the "Fourth International Conference on Fission and Properties of Neutron-Rich nuclei", held at Sanibel Island, Florida, November 11-17, 200