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The multiplicity fluctuations in A+A collisions at SPS and RHIC energies are studied within the HSD transport approach. We find a dominant role of the fluctuations in the nucleon participant number for the final fluctuations. In order to extract physical fluctuations one should decrease the fluctuations in the participants number. This can be done considering very central collisions. The system size dependence of the multiplicity fluctuations in central A+A collisions at the SPS energy range – obtained in the HSD and UrQMD transport models – is presented. The results can be used as a ‘background’ for experimental measurements of fluctuations as a signal of the critical point. Event-by-event fluctuations of the K/p , K/p and p/p ratios in A+A collisions are also studied. Event-by-event fluctuations of the kaon to pion number ratio in nucleus-nucleus collisions are studied for SPS and RHIC energies. We find that the HSD model can qualitatively reproduce the measured excitation function for the K/p ratio fluctuations in central Au+Au (or Pb+Pb) collisions from low SPS up to top RHIC energies. The forward-backward correlation coefficient measured by the STAR Collaboration in Au+Au collisions at RHIC is also studied. We discuss the effects of initial collision geometry and centrality bin definition on correlations in nucleus-nucleus collisions. We argue that a study of the dependence of correlations on the centrality bin definition as well as the bin size may distinguish between these ‘trivial’ correlations and correlations arising from ‘new physics’. 5th International Workshop on Critical Point and Onset of Deconfinement - CPOD 2009, June 08 - 12 2009 Brookhaven National Laboratory, Long Island, New York, USA
We evaluate the in-medium D and -meson masses in hot hadronic matter induced by interactions with the light hadron sector described in a chiral SU(3) model. The e ective Lagrangian approach is generalized to SU(4) to include charmed mesons. We find that the D-mass drops substantially at finite temperatures and densities, which open the channels of the decay of the charmonium states ( 2, c, J/ ) to D pairs in the thermal medium. The e ects of vacuum polarisations from the baryon sector on the medium modification of the D-meson mass relative to those obtained in the mean field approximation are investigated. The results of the present work are compared to calculations based on the QCD sum-rule approach, the quark-meson coupling model, chiral perturbation theory, as well as to studies of quarkonium dissociation using heavy quark potential from lattice QCD.
We calculate open charm and charmonium production in Au + Au reac- tions at ps = 200 GeV within the hadron-string dynamics (HSD) transport approach employing open charm cross sections from pN and N reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm (D + ¯D pairs) is included dynamically. The comover dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e. an interaction strength M2 0 , that is fitted to the J/ suppression data for Pb + Pb collisions at SPS energies. As a novel feature we implement the backward channels for char- monium reproduction by D ¯D channels employing detailed balance. From our dynamical calculations we find that the charmonium recreation is com- parable to the dissociation by comoving mesons. This leads to the final result that the total J/ suppression at ps = 200 GeV as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the comover dissociation is substantial and the backward channels play no role. Furthermore, even in case that all di- rectly produced J/ mesons dissociate immediately (or are not formed as a mesonic state), a sizeable amount of charmonia is found asymptotically due to the D + ! J/ + meson channels in central collisions of Au + Au at ps = 200 GeV which, however, is lower than the J/ yield expected from f pp collis ns.
Abstract: The medium modification of kaon and antikaon masses, compatible with low energy KN scattering data, are studied in a chiral SU(3) model. The mutual interactions with baryons in hot hadronic matter and the e ects from the baryonic Dirac sea on the K( ¯K ) masses are examined. The in-medium masses from the chiral SU(3) e ective model are compared to those from chiral perturbation theory. Furthermore, the influence of these in-medium e ects on kaon rapidity distributions and transverse energy spectra as well as the K, ¯K flow pattern in heavy-ion collision experiments at 1.5 to 2 A·GeV are investigated within the HSD transport approach. Detailed predictions on the transverse momentum and rapidity dependence of directed flow v1 and the elliptic flow v2 are provided for Ni+Ni at 1.93 A·GeV within the various models, that can be used to determine the in-medium K± properties from the experimental side in the near future.
Dynamics of strange, charm and high momentum hadrons in relativistic nucleus nucleus collisions
(2003)
We investigate hadron production and attenuation of hadrons with strange and charm quarks (or antiquarks) as well as high transverse momentum hadrons in relativistic nucleus-nucleus col- lisions from 2 A·GeV to 21.3 A·TeV within two independent transport approaches (UrQMD and HSD). Both transport models are based on quark, diquark, string and hadronic degrees of freedom, but do not include any explicit phase transition to a quark-gluon plasma. From our dynamical calculations we find that both models do not describe the maximum in the K+/ + ratio at 20 - 30 A·GeV in central Au+Au collisions found experimentally, though the excitation functions of strange mesons are reproduced well in HSD and UrQMD. Furthermore, the transport calculations show that the charmonium recreation by D + J/ + meson reactions is comparable to the dissociation by comoving mesons at RHIC energies contrary to SPS energies. This leads to the final result that the total J/ suppression as a function of centrality at RHIC should be less than the suppression seen at SPS energies where the comover dissociation is substantial and the backward channels play no role. Furthermore, our transport calculations in comparison to exper- imental data on transverse momentum spectra from pp, d+Au and Au+Au reactions show that pre-hadronic e ects are responsible for both the hardening of the hadron spectra for low transverse momenta (Cronin e ect) as well as the suppression of high pT hadrons. The mutual interactions of formed hadrons are found to be negligible in central Au+Au collisions at s = 200 GeV for pT e 6 GeV/c and the sizeable suppression seen experimentally is attributed to a large extent to the interactions of leading pre-hadrons with the dense environment.
We study the collective flow of open charm mesons and charmonia in Au + Au collisions at s = 200 GeV within the hadron-string-dynamics (HSD) transport approach. The detailed studies show that the coupling of D, mesons to the light hadrons leads to comparable directed and elliptic flow as for the light mesons. This also holds approximately for J/ mesons since more than 50% of the final charmonia for central and midcentral collisions stem from D + induced reactions in the transport calculations. The transverse momentum spectra of D, mesons and J/ s are only very moderately changed by the (pre-)hadronic interactions in HSD, which can be traced back to the collective flow generated by elastic interactions with the light hadrons. PACS-Nr. 25.75.-q, 13.60.Le, 14.40.Lb, 14.65.Dw
The isospin and strangeness dimensions of the Equation of State are explored. RIA and the SIS200 accelerator at GSI will allow to explore these regions in compressed baryonic matter. 132 Sn + 132 Sn and 100 Sn + 100 Sn collisions as well as the excitation functions of K/pi, Lambda/pi and the centrality dependence of charmonium suppression from the UrQMD and HSD transport models are presented and compared to data. Unambiguous proof for the creation of a 'novel phase of matter' from strangeness and charm yields is not in sight.
The amount of proton stopping in central Pb+Pb collisions from 20–160 A GeV as well as hyperon and antihyperon rapidity distributions are calculated within the UrQMD model in comparison to experimental data at 40, 80, and 160 A GeV taken recently from the NA49 collaboration. Furthermore, the amount of baryon stopping at 160A GeV for Pb+Pb collisions is studied as a function of centrality in comparison to the NA49 data. We find that the strange baryon yield is reasonably described for central collisions, however, the rapidity distributions are somewhat more narrow than the data. Moreover, the experimental antihyperon rapidity distributions at 40, 80, and 160 A GeV are underestimated by up to factors of 3—depending on the annihilation cross section employed—which might be addressed to missing multimeson fusion channels in the UrQMD model. Pacs-Nr.: 25.75.2q, 24.10.Jv, 24.10.Lx
The amount of proton stopping in central Pb+Pb collisions from 20 160 A·GeV as well as hyperon and antihyperon rapidity distributions are calcu- lated within the UrQMD model in comparison to experimental data at 40, 80 and 160 A·GeV taken recently from the NA49 collaboration. Further- more, the amount of baryon stopping at 160 A·GeV for Pb + Pb collisions is studied as a function of centrality in comparison to the NA49 data. We find that the strange baryon yield is reasonably described for central colli- sions, however, the rapidity distributions are somewhat more narrow than the data. Moreover, the experimental antihyperon rapidity distributions at 40, 80 and 160 A·GeV are underestimated by up to factors of 3 - depending on the annihilation cross section employed - which might be addressed to missing multi-meson fusion channels in the UrQMD model. PACS 25.75.+r
We study central collision of Pb + Pb at 20, 40, 80 and 160 A·GeV within the UrQMD transport approach and compare rapidity distributions of ,K+,K and with the recent measurements from the NA49 Collaboration at 40, 80 and 160 A·GeV. It is found that the UrQMD model reasonably describes the data, however, systematically overpredicts the yield by < 20%, whereas the K+ yield is underestimated by < 15%. The K yields are in a good agreement with the experimental data, the yields are also in a reasonable correspondence with the data for all energies. We find that hadronic flavour exchange reactions largely distort the information about the initial strangeness production mechanism at all energies considered. PACS: 25.75.+r
