Latest documents http://publikationen.ub.uni-frankfurt.de/index/index/ Fri, 12 Feb 2010 10:04:46 +0100 Fri, 12 Feb 2010 10:04:46 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20408 Relying on the existing estimates for the production cross sections of mini black holes in models with large extra dimensions, we review strategies for identifying those objects at collider experiments. We further consider a possible stable final state of such black holes and discuss their characteristic signatures. Keywords: Black holes Horst Stöcker; Ben Koch; Marcus Bleicher article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20408 Thu, 02 Dec 2010 10:04:46 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20407 We discuss the present collective flow signals for the phase transition to the quark-gluon plasma (QGP) and the collective flow as a barometer for the equation of state (EoS). We emphasize the importance of the flow excitation function from 1 to 50A GeV: here the hydrodynamicmodel has predicted the collapse of the v1-flow at ~ 10A GeV and of the v2-flow at ~ 40A GeV. In the latter case, this has recently been 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 pB. Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20407 Thu, 02 Dec 2010 09:31:00 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/7163 Background: In this interdisciplinary project, the biological effects of heavy ions are compared to those of X-rays using tissue slice culture preparations from rodents and humans. Advantages of this biological model are the conservation of an organotypic environment and the independency from genetic immortalization strategies used to generate cell lines. Its open access allows easy treatment and observation via live-imaging microscopy. Materials and methods: Rat brains and human brain tumor tissue are cut into 300 micro m thick tissue slices. These slices are cultivated using a membrane-based culture system and kept in an incubator at 37°C until treatment. The slices are treated with X-rays at the radiation facility of the University Hospital in Frankfurt at doses of up to 40 Gy. The heavy ion irradiations were performed at the UNILAC facility at GSI with different ions of 11.4 A MeV and fluences ranging from 0.5–10 x 106 particles/cm². Using 3D-confocal microscopy, cell-death and immune cell activation of the irradiated slices are analyzed. Planning of the irradiation experiments is done with simulation programs developed at GSI and FIAS. Results: After receiving a single application of either X-rays or heavy ions, slices were kept in culture for up to 9d post irradiation. DNA damage was visualized using gamma H2AXstaining. Here, a dose-dependent increase and time-dependent decrease could clearly be observed for the X-ray irradiation. Slices irradiated with heavy ions showed less gamma H2AX-positive cells distributed evenly throughout the slice, even though particles were calculated to penetrate only 90–100 micro m into the slice. Conclusions: Single irradiations of brain tissue, even at high doses of 40 Gy, will result neither in tissue damage visible on a macroscopic level nor necrosis. This is in line with the view that the brain is highly radio-resistant. However, DNA damage can be detected very well in tissue slices using gamma H2AX-immuno staining. Thus, slice cultures are an excellent tool to study radiation-induced damage and repair mechanisms in living tissues. M. Müller; F. Merz; Marco Durante; Volker Seifert; Johannes Rieger; Michel Guy André Mittelbronn; Patrick Nikolaus Harter; Igor Mishustin; Igor Pshenichnov; Franz Rödel; Horst Stöcker; Kosta Schopow; Faramarz Dehghani; Gisela Taucher-Scholz; Ingo Bechmann article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/7163 Tue, 13 Oct 2009 17:44:50 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/6242 The interplay of charmonium production and suppression in In+In and Pb+Pb reactions at 158 AGeV and in Au+Au reactions at sqrt(s)=200 GeV is investigated with the HSD transport approach within the hadronic comover model' and the QGP melting scenario'. The results for the J/Psi suppression and the Psi' to J/Psi ratio are compared to the recent data of the NA50, NA60, and PHENIX Collaborations. We find that, at 158 AGeV, the comover absorption model performs better than the scenario of abrupt threshold melting. However, neither interaction with hadrons alone nor simple color screening satisfactory describes the data at sqrt(s)=200 GeV. A deconfined phase is clearly reached at RHIC, but a theory having the relevant degrees of freedom in this regime (strongly interacting quarks/gluons) is needed to study its transport properties. Elena L. Bratkovskaya; Olena Linnyk; Wolfgang Cassing; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/6242 Fri, 13 Mar 2009 09:25:31 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/927 Schwarze Löcher – das sind im Allgemeinen alles verschlingende, gigantisch schwere astronomische Objekte mit bis zu einigen Milliarden Sonnenmassen. Am Frankfurt Institute for Advanced Studies (FIAS) und am Institut für Theoretische Physik sind in den vergangenen fünf Jahren eine ganz neue Art von Schwarzen Löchern theoretisch vorhergesagt worden, die genau das Gegenteil der astronomisch gemessenen Giganten darstellen, nämlich winzig kleine Schwarze Löcher, so genannte »mini black holes«. Auftreten könnten sie, wenn im kommenden Jahr der neue Teilchenbeschleuniger am CERN in Genf in Betrieb genommen wird. Marcus Bleicher; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/927 Mon, 18 Jun 2007 09:07:52 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/959 We discuss the present collective flow signals for the phase transition to quark-gluon plasma (QGP) and the collective flow as a barometer for the equation of state (EoS). A study of Mach shocks induced by fast partonic jets propagating through the QGP is given. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. Results of a hydrodynamical study of jet energy loss are presented. Horst Stöcker; Barbara Betz; Philip Rau article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/959 Thu, 14 Jun 2007 08:51:49 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/1690 Event-by-event fluctuations of the net baryon number and electric charge in nucleus-nucleus collisions are studied in Pb+Pb at SPS energies within the HSD transport model. We reveal an important role of the fluctuations in the number of target nucleon participants. They strongly influence all measured fluctuations even in the samples of events with rather rigid centrality trigger. This fact can be used to check different scenarios of nucleus-nucleus collisions by measuring the multiplicity fluctuations as a function of collision centrality in fixed kinematical regions of the projectile and target hemispheres. The HSD results for the event-by-event fluctuations of electric charge in central Pb+Pb collisions at 20, 30, 40, 80 and 158 A GeV are in a good agreement with the NA49 experimental data and considerably larger than expected in a quark-gluon plasma. This demonstrate that the distortions of the initial fluctuations by the hadronization phase and, in particular, by the final resonance decays dominate the observable fluctuations. Volodymyr P. Konchakovski; Mark I. Gorenstein; Elena L. Bratkovskaya; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/1690 Fri, 16 Feb 2007 14:50:21 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/1689 Based on the UrQMD transport model, the transverse momentum and the rapidity dependence of the Hanbury-Brown-Twiss (HBT) radii R_L, R_O, R_S as well as the cross term R_OL at SPS energies are investigated and compared with the experimental NA49 and CERES data. The rapidity dependence of the R_L, R_O, R_S is weak while the R_OL is significantly increased at large rapidities and small transverse momenta. The HBT "life-time" issue (the phenomenon that the calculated sqrt R_O^2-R_S^2 value is larger than the correspondingly extracted experimental data) is also present at SPS energies. Qingfeng Li; Marcus Bleicher; Xianglei Zhu; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/1689 Fri, 16 Feb 2007 14:41:50 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/1686 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 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. Laura Tolos; Jürgen Schaffner-Bielich; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/1686 Fri, 16 Feb 2007 14:26:13 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2173 We examine experimental signatures of TeV-mass black hole formation in heavy ion collisions at the LHC. We find that the black hole production results in a complete disappearance of all very high p_T (> 500 GeV) back-to-back correlated di-jets of total mass M > M_f ~ 1 TeV. We show that the subsequent Hawking-decay produces multiple hard mono-jets and discuss their detection. We study the possibility of cold black hole remnant (BHR) formation of mass ~ M_f and the experimental distinguishability of scenarios with BHRs and those with complete black hole decay. Finally we point out that a Heckler-Kapusta-Hawking plasma may form from the emitted mono-jets. In this context we present new simulation data of Mach shocks and of the evolution of initial conditions until the freeze-out. Barbara Betz; Marcus Bleicher; Ulrich Harbach; Thomas J. Humanic; Benjamin Koch; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2173 Tue, 31 Oct 2006 10:01:29 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2172 We propose to measure azimuthal correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions. In particular, we show that hadronic interactions at the late stage cannot significantly disturb the initial back-to-back azimuthal correlations of DDbar pairs. Thus, a decrease or the complete absence of these initial correlations does indicate frequent interactions of heavy-flavor quarks and also light partons in the partonic stage, which are essential for the early thermalization of light partons. Kai Oliver Schweda; Xianglei Zhu; Marcus Bleicher; Shengli Huang; Horst Stöcker; Nu Xu; Pengfei Zhuang preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2172 Tue, 31 Oct 2006 09:40:57 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2171 The experimental signatures of TeV-mass black hole (BH) formation in heavy ion collisions at the LHC is examined. We find that the black hole production results in a complete disappearance of all very high p_T (> 500 GeV) back-to-back correlated di-jets of total mass M > M_f ~ 1 TeV. We show that the subsequent Hawking-decay produces multiple hard mono-jets and discuss their detection. We study the possibility of cold black hole remnant (BHR) formation of mass ~ M_f and the experimental distinguishability of scenarios with BHRs and those with complete black hole decay. Due to the rather moderate luminosity in the first year of LHC running the least chance for the observation of BHs or BHRs at this early stage will be by ionizing tracks in the ALICE TPC. Finally we point out that stable BHRs would be interesting candidates for energy production by conversion of mass to Hawking radiation. Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2171 Tue, 31 Oct 2006 09:23:18 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2170 The concept of Large Extra Dimensions (LED) provides a way of solving the Hierarchy Problem which concerns the weakness of gravity compared with the strong and electro-weak forces. A consequence of LED is that miniature Black Holes (mini-BHs) may be produced at the Large Hadron Collider in p+p collisions. The present work uses the CHARYBDIS mini-BH generator code to simulate the hadronic signal which might be expected in a mid-rapidity particle tracking detector from the decay of these exotic objects if indeed they are produced. An estimate is also given for Pb+Pb collisions. Thomas J. Humanic; Benjamin Koch; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2170 Tue, 31 Oct 2006 09:12:18 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2169 We develop a 1+1 dimensional hydrodynamical model for central heavy-ion collisions at ultrarelativistic energies. Deviations from Bjorken's scaling are taken into account by implementing finite-size profiles for the initial energy density. The calculated rapidity distributions of pions, kaons and antiprotons in central Au+Au collisions at the c.m. energy 200 AGeV are compared with experimental data of the BRAHMS Collaboration. The sensitivity of the results to the choice of the equation of state, the parameters of initial state and the freeze-out conditions is investigated. The best fit of experimental data is obtained for a soft equation of state and Gaussian-like initial profiles of the energy density. Leonid M. Satarov; A.V. Merdeev; Igor N. Mishustin; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2169 Tue, 31 Oct 2006 08:38:30 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2417 The properties of symmetric nuclear matter are investigated in the nonlinear relativistic mean field theory of nuclear matter. We consider the constraints imposed by four nuclear ground state properties on the coupling constants and on the equation of state at zero and at finite temperature. We find that the compression constant K(ρ0) as well as the temperature is irrelevant for the stiffness of the equation of state for m*(ρ0)≤0.7. The main point is that the relativistic mean field theory exhibits acausal and unphysical behavior for compressibilities below K(ρ0)=200 MeV. Every set of coupling constants with a negative quartic coupling constant c is unstable against small quantum fluctuations. B. M. Waldhauser; Joachim A. Maruhn; Horst Stöcker; Walter Greiner article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2417 Fri, 07 Jul 2006 16:20:32 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2451 We present a mechanism for the separation of strangeness from antistrangeness in the deconfinement transition. For a net strangeness of zero in the total system, the population of s quarks is greatly enriched in the quark-gluon plasma, while the s¯ quarks drift into the hadronic phase. This separation could result in ‘‘strangelet’’ formation, i.e., metastable blobs of strange-quark matter, which could serve as a unique signature for quark-gluon plasma formation in heavy-ion collisions. PACS: 25.70.Np, 12.38.Mh Carsten Greiner; Peter Koch; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2451 Tue, 04 Jul 2006 11:25:48 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2577 Collisions of Si(14.5A GeV+Au are investigated in the relativistic-quantum-molecular-dynamics approach. The calculated pseudorapidity distributions for central collisions compare well with recent experimental data, indicating a large degree of nuclear stopping and thermalization. Nevertheless, nonequilibrium effects play an important role in such complex multihadron reactions: They lead to a strong enhancement of the total kaon production cross sections, in good agreement with the experimental data, without requiring the formation of a deconfined quark-gluon plasma. R. Mattiello; Heinz Sorge; Horst Stöcker; Walter Greiner article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2577 Tue, 20 Jun 2006 11:09:35 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2581 Up to now no experimentally feasible method for detecting abnormal nuclear states has been known. We propose to observe them in high-energy heavy-ion collisions through the disappearance of, or irregularities in, high-density nuclear Mach shock phenomena. Jürgen Hofmann; Horst Stöcker; Ulrich Heinz; Werner Scheid; Walter Greiner article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2581 Tue, 20 Jun 2006 10:50:41 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2585 Angular and energy distributions of fragments emitted from fast nucleus-nucleus collisions (Ne--> U at 250, 400, and 800 MeV/N) are calculated with use of nuclear fluid dynamics. A characteristic dependence of the energy spectra and angular distributions on the impact parameter is predicted. The preferential sideward emission of reaction fragments observed in the calculation for nearly central collisions seems to be supported by recent experimental data. Horst Stöcker; Joachim A. Maruhn; Walter Greiner article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2585 Tue, 20 Jun 2006 10:44:52 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2584 We present an analysis of high energy heavy ion collisions at intermediate impact parameters, using a two-dimensional fluid-dynamical model including shear and bulk viscosity, heat conduction, a realistic treatment of the nuclear binding, and an analysis of the final thermal emission of free nucleons. We find large collective momentum transfer to projectile and target residues (the highly inelastic bounce-off effect) and explosion of the hot compressed shock zones formed during the impact. As the calculated azimuthal dependence of energy spectra and angular distributions of emitted nucleons depends strongly on the coefficients of viscosity and thermal conductivity, future exclusive measurements may allow for an experimental determination of these transport coefficients. The importance of 4π measurements with full azimuthal information is pointed out. Gerd Buchwald; László Pal Csernai; Joachim A. Maruhn; Walter Greiner; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2584 Tue, 20 Jun 2006 10:41:14 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2583 Problems arising in viscous nuclear fluid dynamical models of high-energy heavy-ion collisions are discussed. The importance of an accurate treatment of the transport properties of the hot and dense nuclear matter is pointed out. László Pal Csernai; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2583 Tue, 20 Jun 2006 10:34:24 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2613 Two-particle correlation data are presented for the reaction Ar (800 MeV/ nucleon) + Pb. The experimental results are analyzed in the nuclear fluid dynamical and in a linear cascade model. We demonstrate that the collective hydrodynamical correlations dominate the measured two-particle correlation function for the heavy system studied. We discuss the transition from the early stages of the reaction which are governed by few nucleon correlations, to the later stages with their macroscopic flow which can only be reached using heavy colliding systems. The sensitivity of the correlation data on the underlying compressional dissipative processes is analyzed. László Pal Csernai; Walter Greiner; Horst Stöcker; Isao Tanihata; Shoji Nagamiya; Jörn Knoll article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2613 Tue, 13 Jun 2006 12:56:53 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2625 The fluid dynamical model is used to study the reactions 20Ne+238U and 40Ar+40Ca at Elab=390 MeV/nucleon. The calculated double differential cross sections d2σ/dΩdE exhibit sidewards maxima in agreement with recent experimental data. The azimuthal dependence of the triple differential distributions, to be obtained from an event-by-event analysis of 4π exclusive experiments, can yield deeper insight into the collision process: Jets of nuclear matter are predicted with a strongly impact-parameter-dependent thrust angle θjet(b). NUCLEAR REACTIONS Ar+Ca, Ne+U, Elab=393 MeV/nucleon, fluid dynamics with thermal breakup, double differential cross sections, azimuthal dependence of triple differential cross sections, event-by-event thrust analysis of 4π exclusive experiments. Horst Stöcker; László Pal Csernai; Gerhard Graebner; Gerd Buchwald; Hans Kruse; R. Y. Cusson; Joachim A. Maruhn; Walter Greiner article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2625 Tue, 13 Jun 2006 12:52:18 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2623 Intermediate-rapidity fragments with A=1-14 emitted from 42-137-MeV/nucleon Ar + Au have been measured. Evidence is presented that these fragments arise from a common moving source. Entropy values are extracted from the mass distributions by use of quantum statistical and Hauser-Feshbach theories. The extracted entropy values of S/A≈2-2.4 are much smaller than the values expected from measured deuteron-to-proton ratios, but are still considerably higher than theoretically predicted values. B. V. Jacak; G. D. Westfall; C. K. Gelbke; L.H. Harwood; W. G. Lynch; D.K. Scott; Horst Stöcker; M.B. Tsang; T. J. M. Symons article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2623 Tue, 13 Jun 2006 12:47:32 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2622 Proton spectra have been calculated for the reaction 12C(85 MeV/nucleon) + 197Au using a three-dimensional hydrodynamical model with viscosity and thermal conductivity and final thermal breakup. The theoretical results are compared to recent data. It is shown that the predicted flow effects are not observable as a result of the impact parameter averaging inherent in the inclusive proton spectra. In contrast, angular distributions of medium mass nuclei (A>3) in nearly central collisions can provide signatures for flow effects. Gerd Buchwald; Gerhard Graebner; J. Theis; Joachim A. Maruhn; Walter Greiner; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2622 Tue, 13 Jun 2006 12:42:16 +0200