Latest documents http://publikationen.ub.uni-frankfurt.de/index/index/ Wed, 16 Nov 2005 09:44:27 +0100 Wed, 16 Nov 2005 09:44:27 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3297 Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 23 S. Agostinelli; Dennis Dean Dietrich; Walter Greiner; Kerstin Anja Paech; Stefan Scherer; Horst Stöcker; Henning Weber; Detlef Zschiesche; et al.; Geant4 Collaboration article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3297 Wed, 16 Nov 2005 09:44:27 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3333 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. Elena L. Bratkovskaya; Wolfgang Cassing; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3333 Mon, 14 Nov 2005 10:57:58 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3303 A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the e ects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarisation e ects from the nucleon sector and is not observed in the mean field approximation. Detlef Zschiesche; Amruta Mishra; Stefan Schramm; Horst Stöcker; Walter Greiner preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3303 Mon, 14 Nov 2005 10:38:37 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3302 We introduce a model for the real-time evolution of a relativistic fluid of quarks coupled to non-equilibrium dynamics of the long wavelength (classical) modes of the chiral condensate. We solve the equations of motion numerically in 3+1 spacetime dimensions. Starting the evolution at high temperature in the symmetric phase, we study dynamical trajectories that either cross the line of first-order phase transitions or evolve through its critical endpoint. For those cases, we predict the behavior of the azimuthal momentum asymmetry for highenergy heavy-ion collisions at nonzero impact parameter. Kerstin Paech; Horst Stöcker; Adrian Dumitru preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3302 Mon, 14 Nov 2005 10:24:38 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3307 The J/psi yield at midrapidity at the top RHIC (relativistic heavy ion collider) energy is calculated within the statistical coalescence model, which assumes charmonium formation at the late stage of the reaction from the charm quarks and antiquarks created earlier in hard parton collisions. The results are compared to the new PHENIX data and to predictions of the standard models, which assume formation of charmonia exclusively at the initial stage of the reaction and their subsequent suppression. Two versions of the suppression scenario are considered. One of them assumes gradual charmonium suppression by comovers, while the other one supposes that the suppression sets in abruptly due to quark-gluon plasma formation. Surprisingly, both versions give very similar results. In contrast, the statistical coalescence model predicts a few times larger J/psi yield in the most central collisions. Andriy P. Kostyuk; Mark I. Gorenstein; Horst Stöcker; Walter Greiner preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3307 Mon, 14 Nov 2005 10:18:10 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3308 The SENECA model, a new hybrid approach to air shower simulations, is presented. It combines the use of e cient 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 e cient 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. Hans-Joachim Drescher; Glennys R. Farrar; Marcus Bleicher; Manuel Reiter; Sven Soff; Horst Stöcker article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3308 Mon, 14 Nov 2005 10:15:24 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3319 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. Hans-Joachim Drescher; Marcus Bleicher; Sven Soff; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3319 Thu, 10 Nov 2005 10:46:24 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3318 We discuss the new data for the production of the psi meson in pA collisions at 450 GeV at CERNSPS (of the NA50-collaboration) [1]. We extract from the CERN data sigma(psi'N) 8 mb under the assumption that the psi is produced as a result of the space-time evolution of a point-like c¯c pair which expands with time to the full size of the charmonium state. In the analysis we assume the existence of a relationship between the distribution of color in a hadron and the cross section of its interaction with a nucleon. However, our result is rather sensitive to the pattern of the expansion of the wave packet and significantly larger values of sigma(psi'N)are not ruled out by the data. We show that recent CERN data confirm the suggestion of ref. [2] that color fluctuations of the strengths in charmonium-nucleon interaction are the major source of suppression of the J/psi yield as observed at CERN in both pA and AA collisions. Lars Gerland; Leonid Frankfurt; Mark Strikman; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3318 Thu, 10 Nov 2005 10:42:14 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3324 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. Amruta Mishra; Elena L. Bratkovskaya; Jürgen Schaffner-Bielich; Stefan Schramm; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3324 Thu, 10 Nov 2005 10:34:59 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3325 Abstract: The e ect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The e ect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This e ect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation (RHA), where the baryon self energy is modified due to interactions with both the non-strange ( ) and the strange ( ) scalar fields. Amruta Mishra; K. Balazs; Detlef Zschiesche; Stefan Schramm; Horst Stöcker; Walter Greiner preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3325 Thu, 10 Nov 2005 10:29:25 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3326 The N/Z ratio of free nucleons from collisions of neutron-rich nuclei as a function of their momentum is studied by means of Isospin dependent Quantum Molecular Dynamics. We find that this ratio is not only sensitive to the form of the density dependence of the symmetry potential energy but also its strength determined by the symmetry energy coe cient. The uncertainties about the symmetry energy coe cient influence the accuracy of probing the density dependence of the symmetry energy by means of the N/Z ratio of free nucleons of neutron-rich nuclei. Qingfeng Li; Zhuxia Li; Enguang Zhao; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3326 Thu, 10 Nov 2005 10:24:17 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3317 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. Wolfgang Cassing; Kai Gallmeister; Elena L. Bratkovskaya; Carsten Greiner; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3317 Wed, 09 Nov 2005 11:24:32 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3371 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. Manuel Reiter; Elena L. Bratkovskaya; Marcus Bleicher; Wolfgang Bauer; Wolfgang Cassing; Henning Weber; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3371 Tue, 01 Nov 2005 13:03:50 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3407 Modifications of the gyromagnetic moment of electrons and muons due to a minimal length scale combined with a modified fundamental scale M_f are explored. Deviations from the theoretical Standard Model value for g-2 are derived. Constraints for the fundamental scale M_f are given. Ulrich Harbach; Sabine Hossenfelder; Marcus Bleicher; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3407 Thu, 27 Oct 2005 16:28:16 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3406 A micro-canonical treatment is used to study particle production in pp collisions. First this micro-canonical treatment is compared to some canonical ones. Then proton, antiproton and pion 4 pi multiplicities from proton-proton collisions at various center of mass energies are used to fix the micro-canonical parameters (E) and (V). The dependences of the micro-canonical parameters on the collision energy are parameterised for the further study of pp reactions with this micro-canonical treatment. Fu-Ming Liu; Klaus Werner; Jörg Aichelin; Marcus Bleicher; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3406 Thu, 27 Oct 2005 16:27:31 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3423 Yields, rapidity and transverse momentum spectra of Delta++(1232), Lambda(1520), Sigma+-(1385) and the meson resonances K0(892), Phi, rho0 and f0(980) are predicted. Hadronic rescattering leads to a suppression of reconstructable resonances, especially at low p_perp. A mass shift of the rho of 10 MeV is obtained from the microscopic simulation, due to late stage rho formation in the cooling pion gas. Marcus Bleicher; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3423 Thu, 27 Oct 2005 16:23:29 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3416 Recent calculations applying statistical mechanics indicate that in a setting with compactified large extra dimensions a black hole might evolve into a (quasi-)stable state with mass close to the new fundamental scale M f. Black holes and therefore their relics might be produced at the LHC in the case of extra-dimensional topologies. In this energy regime, Hawking's evaporation scenario is modified due to energy conservation and quantum effects. We reanalyse the evaporation of small black holes including the quantisation of the emitted radiation due to the finite surface of the black hole. It is found that observable stable black hole relics with masses sim 1-3 M f would form which could be identified by a delayed single jet with a corresponding hard momentum kick to the relic and by ionisation, e.g. in a TPC. Sabine Hossenfelder; Marcus Bleicher; Stefan Hofmann; Horst Stöcker; Ashutosh V. Kotwal preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3416 Thu, 27 Oct 2005 16:18:53 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3415 String theory suggests the existence of a minimum length scale. An exciting quantum mechanical implication of this feature is a modification of the uncertainty principle. In contrast to the conventional approach, this generalised uncertainty principle does not allow to resolve space time distances below the Planck length. In models with extra dimensions, which are also motivated by string theory, the Planck scale can be lowered to values accessible by ultra high energetic cosmic rays (UHECRs) and by future colliders, i.e. M f approximately equal to 1 TeV. It is demonstrated that in this novel scenario, short distance physics below 1/M f is completely cloaked by the uncertainty principle. Therefore, Planckian effects could be the final physics discovery at future colliders and in UHECRs. As an application, we predict the modifications to the e+ e- to f+ f- cross-sections. Sabine Hossenfelder; Marcus Bleicher; Stefan Hofmann; Jörg Ruppert; Stefan Scherer; Horst Stöcker preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3415 Thu, 27 Oct 2005 16:18:06 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/4818 We investigate transverse hadron spectra from relativistic nucleus-nucleus collisions which reflect important aspects of the dynamics - such as the generation of pressure - in the hot and dense zone formed in the early phase of the reaction. Our analysis is performed within two independent transport approaches (HSD and UrQMD) 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 at bombarding energies above ~ 5 A.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 ~ 5 A.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. Elena L. Bratkovskaya; Sven Soff; Horst Stöcker; M. van Leeuwen; Wolfgang Cassing preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/4818 Wed, 13 Apr 2005 17:05:33 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/4814 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 both 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+/Pi+ 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 K +/- m-theta-spectra have a larger inverse slope parameter than expected from the calculations. The approximately constant slope of 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. Elena L. Bratkovskaya; Marcus Bleicher; Wolfgang Cassing; M. van Leeuwen; Manuel Reiter; Sven Soff; Horst Stöcker; Henning Weber preprint http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/4814 Wed, 13 Apr 2005 16:18:08 +0200