[Show abstract][Hide abstract] ABSTRACT: Several observables of unbound nucleons which are to some extent sensitive to the medium modifications of nucleon-nucleon elastic cross sections in neutron-rich intermediate energy heavy ion collisions are investigated. The splitting effect of neutron and proton effective masses on cross sections is discussed. It is found that the transverse flow as a function of rapidity, the $Q_{zz}$ as a function of momentum, and the ratio of halfwidths of the transverse to that of longitudinal rapidity distribution $R_{t/l}$ are very sensitive to the medium modifications of the cross sections. The transverse momentum distribution of correlation functions of two-nucleons does not yield information on the in-medium cross section. Comment: 14 pages, 5 figures
Journal of Physics G Nuclear and Particle Physics 01/2006; 32(4). DOI:10.1088/0954-3899/32/4/001 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Transverse hadron spectra from proton–proton, proton–nucleus and nucleus–nucleus collisions from 2 <i?A</i?·GeV to 21.3 <i?A</i?·TeV are investigated within two independent transport approaches (HSD and UrQMD). For central Au+Au (Pb+Pb) collisions at energies above <i?E</i?lab ~ 5 <i?A</i?·GeV, the measured K± transverse mass spectra have a larger inverse slope parameter than expected from the default calculations. The additional pressure — as supported by lattice QCD calculations at finite quark chemical potential μ<i?q</i? and temperature <i?T</i? — might be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions E.L. Bratkovskaya et al., <i?Phys. Rev. C</i? <b?69</b? (2004) 054907.
[Show abstract][Hide abstract] ABSTRACT: The influence of the isospin-independent, isospin- and momentum-dependent equation of state (EoS), as well as the Coulomb interaction on the pion production in intermediate energy heavy ion collisions (HICs) is studied for both isospin-symmetric and neutron-rich systems. The Coulomb interaction plays an important role in the reaction dynamics, and strongly influences the rapidity and transverse momentum distributions of charged pions. It even leads to the $\pi^-/\pi^+$ ratio deviating slightly from unity for isospin-{\it symmetric} systems. The Coulomb interaction between mesons and baryons is also crucial for reproducing the proper pion flow since it changes the behavior of the directed and the elliptic flow components of pions visibly. The EoS can be better investigated in neutron-rich system if {\it multiple} probes are measured simultaneously. For example, the rapidity and the transverse momentum distributions of the charged pions, the $\pi^-/\pi^+$ ratio, the various pion flow components, as well as the {\it difference} of $\pi^+$-$\pi^-$ flows. A new sensitive observable is proposed to probe the symmetry potential energy at high densities, namely the transverse momentum distribution of the elliptic flow difference [$\Delta v_2^{\pi^+ - \pi^-}(p_t^{\rm c.m.})$]. Comment: 21 pages, 10 figs, 1 table, submitted to Phys. Rev. C
Journal of Physics G Nuclear and Particle Physics 09/2005; 32(2). DOI:10.1088/0954-3899/32/2/007 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Based on the ultrarelativistic quantum molecular dynamics (UrQMD) model, the effects of the density-dependent symmetry potential for baryons and of the Coulomb potential for produced mesons are investigated for neutron-rich heavy ion collisions at intermediate energies. The calculated results of the $\Delta^-/\Delta^{++}$ and $\pi ^{-}/\pi ^{+}$ production ratios show a clear beam-energy dependence on the density-dependent symmetry potential, which is stronger for the $\pi ^{-}/\pi ^{+}$ ratio close to the pion production threshold. The Coulomb potential of the mesons changes the transverse momentum distribution of the $\pi ^{-}/\pi ^{+}$ ratio significantly, though it alters only slightly the $\pi^-$ and $\pi^+$ total yields. The $\pi^-$ yields, especially at midrapidity or at low transverse momenta and the $\pi^-/\pi^+$ ratios at low transverse momenta, are shown to be sensitive probes of the density-dependent symmetry potential in dense nuclear matter. The effect of the density-dependent symmetry potential on the production of both, K$^0$ and K$^+$ mesons, is also investigated. Comment: 28 pages in RevTex, 11 figures, 1 table, submitted to Journal of Physics G
Journal of Physics G Nuclear and Particle Physics 07/2005; 31(11). DOI:10.1088/0954-3899/31/11/016 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the sensitivity of several observables to the density dependence of the symmetry potential within the microscopic transport model UrQMD (ultrarelativistic quantum molecular dynamics model). The same systems are used to probe the symmetry potential at both low and high densities. The influence of the symmetry potentials on the yields of $\pi^{-}$, $\pi^{+}$, the $\pi^{-}/\pi^{+}$ ratio, the $n/p$ ratio of free nucleons and the $t/^3$He ratio are studied for neutron-rich heavy ion collisions ($^{208}Pb+^{208}Pb$, $^{132}Sn+^{124}Sn$, $^{96}Zr+^{96}Zr$) at $E_b=0.4A {\rm GeV}$. We find that these multiple probes provides comprehensive information on the density dependence of the symmetry potential. Comment: 15 pages, 7 figures, 2 tables. Submitted to Phys. Rev. C
Physical Review C 06/2005; 72(3). DOI:10.1103/PhysRevC.72.034613 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We review the results from the various hydrodynamical and transport models on the collective flow observables from AGS to RHIC energies. A critical discussion of the present status of the CERN experiments on hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A$\cdot$GeV: here the hydrodynamic model has predicted the collapse of the $v_1$-flow and of the $v_2$-flow at $\sim 10$ A$\cdot$GeV; at 40 A$\cdot$GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as evidence for a first order phase transition at high baryon density $\rho_B$. Moreover, the connection of the elliptic flow $v_2$ to jet suppression is examined. It is proven experimentally that the collective flow is not faked by minijet fragmentation. Additionally, detailed transport studies show that the away-side jet suppression can only partially ($<$ 50%) be due to hadronic rescattering. Furthermore, the change in sign of $v_1, v_2$ closer to beam rapidity is related to the occurence of a high density first order phase transition in the RHIC data at 62.5, 130 and 200 A$\cdot$GeV. Comment: 15 pages, 7 eps figures, to be published in J. Phys. G - Proceedings of SQM 2004
Journal of Physics G Nuclear and Particle Physics 12/2004; 31(6). DOI:10.1088/0954-3899/31/6/037 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A critical discussion of the present status of the CERN experiments on
charm dynamics and hadron collective flow is given. We emphasize the
importance of the flow excitation function from 1 to 50 A.GeV: here the
hydrodynamic model has predicted the collapse of the v1-flow and of the
v2-flow at ~ 10 A.GeV at 40 A.GeV it has been recently observed by the
NA49 collaboration. Since hadronic rescattering models predict much
larger flow than observed at this energy we interpret this observation
as potential evidence for a first order phase transition at high baryon
density ρB. A detailed discussion of the collective flow as a
barometer for the equation of state (EoS) of hot dense matter at RHIC
follows. Additionally, detailed transport studies show that the
away-side jet suppression can only partially (< 50%) be due to
hadronic rescattering. We, finally, propose upgrades and second
generation experiments at RHIC which inspect the first order phase
transition in the fragmentation region, i.e. at μB ~ 400 MeV (y ~ 4 -
5), where the collapse of the proton flow should be seen in analogy to
the 40 A.GeV data. The study of Jet-Wake-riding potentials and Bow
shocks - caused by jets in the QGP formed at RHIC - can give further
information on the equation of state (EoS) and transport coefficients of
the Quark Gluon Plasma (QGP).
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Physics G Nuclear and Particle Physics 10/2004; 30(12):L35. DOI:10.1088/0954-3899/30/12/L01 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The influence of high and low energy hadronic models on lateral distribution functions of cosmic ray air showers for Auger energies is explored. A large variety of presently used high and low energy hadron interaction models are analysed and the resulting lateral distribution functions are compared. We show that the slope depends on both the high and low energy hadronic model used. The models are confronted with available hadron–nucleus data from accelerator experiments.
[Show abstract][Hide abstract] ABSTRACT: We investigate hadron production and transverse hadron spectra in nucleus-nucleus collisions from 2 $A\cdot$GeV to 21.3 $A\cdot$TeV within two independent transport approaches (UrQMD and HSD) based on quark, diquark, string and hadronic degrees of freedom. The enhancement of pion production in central Au+Au (Pb+Pb) collisions relative to scaled $pp$ collisions (the 'kink') is described well by both approaches without involving a phase transition. However, the maximum in the $K^+/\pi^+$ ratio at 20 to 30 A$\cdot$GeV (the 'horn') is missed by $\sim$ 40%. Also, at energies above $\sim$ 5 A$\cdot$GeV, the measured $K^{\pm}$ $m_{T}$-spectra have a larger inverse slope than expected from the models. Thus the pressure generated by hadronic interactions in the transport models at high energies is too low. This finding suggests that the additional pressure - as expected from lattice QCD at finite quark chemical potential and temperature - might be generated by strong interactions in the early pre-hadronic/partonic phase of central heavy-ion collisions. Finally, we discuss the emergence of density perturbations in a first-order phase transition and why they might affect relative hadron multiplicities, collective flow, and hadron mean-free paths at decoupling.
[Show abstract][Hide abstract] ABSTRACT: We investigate hadron production as well as transverse hadron spectra from proton-proton, proton-nucleus and nucleus-nucleus collisions from 2 $A\cdot$GeV to 21.3 $A\cdot$TeV within two independent transport approaches (HSD and UrQMD) that are based on quark, diquark, string and hadronic degrees of freedom. The comparison to experimental data on transverse mass spectra from $pp$, $pA$ and C+C (or Si+Si) reactions shows the reliability of the transport models for light systems. For central Au+Au (Pb+Pb) collisions at bombarding energies above $\sim$ 5 A$\cdot$GeV, furthermore, the measured $K^{\pm}$ transverse mass spectra have a larger inverse slope parameter than expected from the default calculations. We investigate various scenarios to explore their potential effects on the $K^\pm$ spectra. In particular the initial state Cronin effect is found to play a substantial role at top SPS and RHIC energies. However, the maximum in the $K^+/\pi^+$ ratio at 20 to 30 A$\cdot$GeV is missed by ~40% and the approximately constant slope of the $K^\pm$ spectra at SPS energies is not reproduced either. Our systematic analysis suggests that the additional pressure - as expected from lattice QCD calculations at finite quark chemical potential $\mu_q$ and temperature $T$- should be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions. Comment: 20 pages, 15 figures, Phys. Rev. C, in press
Physical Review C 02/2004; 69(5). DOI:10.1103/PhysRevC.69.054907 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate transverse hadron spectra from relativistic nucleus-nucleus collisions within two independent transport approaches that are based on quark, diquark, string, and hadronic degrees of freedom. Both transport models show their reliability for elementary pp as well as light-ion (C+C, Si+Si) reactions. However, for central Au+Au (Pb+Pb) collisions above approximately 5A GeV the measured K+/- transverse mass spectra have a larger inverse slope parameter than expected from the calculation. Thus, the pressure generated by hadronic interactions in the transport models above approximately 5A GeV is lower than observed in the experimental data. This finding shows that the additional pressure--as expected from lattice QCD calculations at finite quark chemical potential and temperature--is generated by strong partonic interactions in the early phase of central Au+Au (Pb+Pb) collisions.
[Show abstract][Hide abstract] ABSTRACT: We review the recent developments on microscopic transport calculations for two-particle correlations at low relative momenta in ultrarelativistic heavy ion collisions at RHIC.
Acta Physica Polonica Series B 01/2004; 35(1). · 0.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate hadron production as well as transverse hadron spectra in nucleus–nucleus collisions from 2 A GeV to 21.3 A TeV within two independent transport approaches (UrQMD and HSD) that are based on quark, diquark, string and hadronic degrees of freedom. The comparison to experimental data demonstrates that the two approaches agree quite well with each other and with the experimental data on hadron production. The enhancement of pion production in central Au+Au (Pb+Pb) collisions relative to scaled pp collisions (the ‘kink’) is well described by both approaches without involving any phase transition. However, the maximum in the K+/π+ ratio at 20 to 30 A GeV (the ‘horn’) is missed by ∼40%. A comparison to the transverse mass spectra from pp and C+C (or Si+Si) reactions shows the reliability of the transport models for light systems. For central Au+Au (Pb+Pb) collisions at bombarding energies above ∼5 A GeV, however, the measured spectra have a larger inverse slope parameter than expected from the calculations. The approximately constant slope of the K± spectra at SPS (the ‘step’) is not reproduced either. Thus the pressure generated by hadronic interactions in the transport models above ∼5 A GeV is lower than observed in the experimental data. This finding suggests that the additional pressure—as expected from lattice QCD calculations at finite quark chemical potential and temperature—might be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions.
Progress in Particle and Nuclear Physics 01/2004; 53(1-53):225-237. DOI:10.1016/j.ppnp.2004.02.015 · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We review recent developments in the field of microscopic transport model calculations for ultrarelativistic heavy ion collisions. In particular, we focus on the strangeness production, for example, the phi-meson and its role as a messenger of the early phase of the system evolution. Moreover, we discuss the important effects of the (soft) field properties on the multiparticle system. We outline some current problems of the models as well as possible solutions to them. Comment: Invited talk at the 7th International Conference on Strangeness in Quark Matter, SQM 2003, Atlantic Beach, North Carolina, USA, 12-17 Mar, 2003. 11 pages, 12 figures
Journal of Physics G Nuclear and Particle Physics 12/2003; 30(1). DOI:10.1088/0954-3899/30/1/013 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The SENECA model, a new hybrid approach to air shower simulations, is presented. It combines the use of efficient cascade equations in the energy range where a shower can be treated as one-dimensional, with a traditional Monte Carlo method which traces individual particles. This allows one to reproduce natural fluctuations of individual showers as well as the lateral spread of low energy particles. The model is quite efficient in computation time. As an application of the new approach, the influence of the low energy hadronic models on shower properties for AUGER energies is studied. We conclude that these models have a significant impact on the tails of lateral distribution functions, and deserve therefore more attention.
[Show abstract][Hide abstract] ABSTRACT: We present calculations of two-pion and two-kaon correlation functions in relativistic heavy ion collisions from a relativistic transport model that includes explicitly a first-order phase transition from a thermalized quark-gluon plasma to a hadron gas. We compare the obtained correlation radii with recent data from RHIC. The predicted Rside radii agree with data while the Rout and Rlong radii are overestimated. We also address the impact of in-medium modifications, for example, a broadening of the ϱ-meson, on the correlation radii. In particular, the longitudinal correlation radius Rlong is reduced, improving the comparison to data.
Nuclear Physics A 03/2003; 715(715). DOI:10.1016/S0375-9474(02)01492-6 · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We calculate the antibaryon-to-baryon ratios, , and for Au+Au collisions at RHIC ( GeV). The effects of strong color fields associated with an enhanced strangeness and diquark production probability and with an effective decrease of formation times are investigated. Antibaryon-to-baryon ratios increase with the color field strength. The ratios also increase with the strangeness content |S|. The netbaryon number at midrapidity considerably increases with the color field strength while the netproton number remains roughly the same. This shows that the enhanced baryon transport involves a conversion into the hyperon sector (hyperonization) which can be observed in the ratio.
Physics Letters B 09/2002; 551(1-2-551):115-120. DOI:10.1016/S0370-2693(02)03019-8 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We discuss predictions for the pion and kaon interferometry measurements in relativistic heavy ion collisions at SPS and RHIC energies. In particular, we confront relativistic transport model calculations that include explicitly a first-order phase transition from a thermalized quark-gluon plasma to a hadron gas with recent data from the RHIC experiments. We critically examine the "HBT-puzzle" both from the theoretical as well as from the experimental point of view. Alternative scenarios are briefly explained.
[Show abstract][Hide abstract] ABSTRACT: The article looks back on the 183 workshops and briefing sessions of the 15 annual UKSG conferences from 1990 to 2004. The content of this particular form of professional training reflects the development of the professional environment, interests and activities of librarians, especially the emergence of the digital library. Nine major subjects of information and debate are identified: human resource management, new software, acquisition of e-serials, legal aspects, emerging standards, usage statistics, library/vendor relationship, document delivery, and publishing. An analysis of attendance and some remarks on specific features of the sessions complete this “historical study”.
Physics Letters B 03/2002; 446(3-4). DOI:10.1016/S0370-2693(98)01566-4 · 6.13 Impact Factor