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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
This article generalizes Schwinger’s mechanism for particles production in the arbitrary finite field volume. McLerran-Venugopolan(MV) model and iterative solution of DGLAP equation in the double leading log approximation for small x gluon distribution function were used to derive the new formula for initial chromofield energy density. This initial chromofield energy is distributed among color neutral clusters or strings of different length. This strings are stretched by receding nucleus. From the proposed mechanism of string fragmentation or color field decay based on exact solution of Dirac equation in the different finite volume, the new formulae for esimated baryon kinetic energy loss and rapidity spectrum of produced partons were derived.
Zukunftsforschung ohne Orakel : zur langfristigen Szenarienbildung und der Initiative "Zukunft 25"
(2007)
Jedes Jahrhundert bringt eigene Visionen der Zukunft hervor, wobei vor allem diejenigen Entwicklungen extrapoliert werden, die in der aktuellen Forschung besonders präsent sind. Im 19. Jahrhundert waren dies, wie die gezeigten Sammelbilder belegen, vor allem Verkehr und Mobilität. In seinem Roman »In 80 Tagen um die Erde« drückt Jules Verne die Faszination darüber aus, dass Orte und Menschen zusammenrücken, weil die Entfernungen sich dank moderner Verkehrsmittel wie Auto, Eisenbahn und Flugzeug schneller überbrücken lassen. Die überwiegend optimistischen Zukunftserwartungen des 19. Jahrhunderts sind inzwischen kritischeren, wenn nicht pessimistischen Visionen gewichen. Betrachtet man Filme wie »Blade Runner« oder »Matrix«, so beschäftigen uns heute Themen wie der künstliche oder manipulierte Mensch. Auch der Zukunftsforscher Claudius Gros denkt über die Folgen einer künstlichen Gebärmutter nach. Aber er sieht optimistisch in die Zukunft.
Der Nobelpreisträger Hans Albrecht Bethe war einer der ganz großen Physiker des 20. Jahrhunderts. Er gilt als einer der Väter der modernen Quantenphysik. In seiner Bedeutung für die Entwicklung der modernen Physik kommt er selbst Werner Heisenberg oder Max Planck sehr nahe. Er ist in Frankfurt aufgewachsen, hat hier das Goethe-Gymnasium besucht und an der Universität Frankfurt studiert. 1933 musste er emigrieren, da seine Mutter jüdischen Glaubens war. In seiner Heimatstadt Frankfurt ist er bisher fast unbekannt geblieben. Aus Sorge, dass Hitler-Deutschland »die Bombe« zuerst bauen könnte, unterstützte Bethe die USA bei der Entwicklung der Atombombe. Robert Oppenheimer holte ihn 1941 zum Manhattan Project nach Los Alamos (New Mexico). Hans Bethe war der führende theoretische Konstrukteur der Bombe. Doch Zeit seines Lebens glaubte er, damit das Falsche getan zu haben. Nach dem Krieg engagierte er sich für die Rüstungskontrolle. Bethe initiierte 1959 die Genfer Konferenz führender Forscher zur Empfehlung eines kontrollierten Teststoppabkommens und beriet den damaligen US-Präsidenten Dwight Eisenhower bei Fragen zur Einstellung von Kernwaffenversuchen. Er war in den USA und weltweit ein Wissenschaftler mit großem politischem und moralischem Einfluss. ...
The work presented in this thesis addresses a key issue of the CBM experiment at FAIR, which aims to study charm production in heavy ion collisions at energies ranging from 10 to 40 AGeV . For the first time in this kinematical range, open charm mesons will be used as a probe of the nuclear fireball. Despite of their short decay length, which is typically in the order of few 100 µm in the laboratory frame, those mesons will be identified by reconstructing their decay vertex.
Quantum chromodynamics predicts the existence of a phase transition from hadronic to quark-gluon matter when temperature and pressure are sufficiently high. Colliding heavy nuclei at ultra-relativistic speeds allows to deposit large amounts of energy in a small volume of space, and is the only available experimental mean to produce the extreme conditions necessary to obtain the deconfined state. Numerous models and ideas were developed in the last decades to study heavy ion physics and understand the properties of extremely heated and compressed nuclear matter. With the ever increasing energy available in the center of mass frame (and thus number of particles produced) and the development of large acceptance detectors, it has become possible to study the fluctuations of physical quantities on an event-by-event basis, and access thermodynamical properties not present in particle spectra. The characteristics of the highly excited matter produced, e.g. thermalization, effect of resonance decay. . . can be investigated by fluctuation analyses. In fact, fluctuations are good indicators for a phase transition and a plethora of fluctuation probes have been proposed to pin down the existence and the properties of the QGP. We study various fluctuation quantities within the Ultra-relativistic Quantum Molecular Dynamics UrQMD and the quantum Molecular Dynamics qMD models. UrQMD is based on hadron and string degrees of freedom and allows to disentangle purely hadronic effects. In contrast, the qMD model includes an explicit transition from quark to hadronic matter and can serve to test adequate probes of the initial QGP state. We show that the qMD model can reasonably reproduce various experimental particles rapidity distributions and transverse mass spectra in wide energy range. Within the frame of the dynamical recombination procedure used in qMD, we study the enhancement of protons over pions (p/π) ratio in the intermediate pt range (1.5 < pt < 2.5). We show that qMD can reproduce the large p/π ≈ 1 observed experimentally at RHIC energies at hadronization. However, the subsequent decay of resonances makes the ratio fall to values incompatible with experimental data. We thus conclude that resonance decay might have a drastic influence on this observable in the quark recombination picture. Charged particles multiplicity fluctuations measured at SPS by the NA49 collaboration are enhanced in midperipheral events for Pb+Pb collisions at Elab = 160 AGeV. This feature is not reproduce by hadron-string transport approaches, which show a flat centrality dependence, within the proper experimental acceptance and with the proper centrality selection procedure. However, we show that the behavior of multiplicity fluctuations in transport codes is similar to the experimental result in full 4π acceptance. We identify the centrality selection procedure as the reason for the enhanced particle multiplicity fluctuations in midperipheral reactions and argue that it can be used to distinguish between different scenarios of particle productions. We show that experimental data might indicate a strong mixing of projectile and target related production sources. Strangeness over entropy K/π and baryon number over entropy p/π ratio fluctuations have been measured by the NA49 experiment in the SPS energy range, from Elab = 20 AGeV up to Elab = 160 AGeV. We investigate the sensitivity of this observable to kinematical cuts and discuss the influence of resonance decay. We find the dynamical p/π ratio fluctuations to increase with beam energy, in agreement with the measured data points. On the contrary, the dynamical K/π ratio fluctuations are essential flat as a function of centrality and depend only weakly on the kinematical cuts applied. Our results are in line with the simulations performed earlier by the NA49 collaboration in their detector acceptance filter. Finally, we focus on the correlations and fluctuations of conserved charges. It was proposed that these fluctuations are sensitive to the fractional charge carried by the quarks in the initial QGP stage and survive the whole course of heavy ion reactions. A crucial point is the influence of hadronization that may relax the initial QGP fluctuation/correlation signals to their hadronic values. We use the quark Molecular Dynamics qMD model to disentangle the effect of recombination-hadronization on charged particles ratio fluctuations, charge transfer fluctuations, baryon number-strangeness correlation coefficient and various ratios of susceptibilities (i.e. correlations over fluctuations). We find that the dynamical recombination procedure implemented in the qMD model destroys all studied initial QGP fluctuations and correlations and might ex- plain why no signal of a phase transition based on event-by-event fluctuations was found in the experimental data until now.
We study various fluctuation and correlation signals of the deconfined state using a dynamical recombination approach (quark Molecular Dynamics, qMD). We analyse charge ratio fluctuations, charge transfer fluctuations and baryon-strangeness correlations as a function of the center of mass energy with a set of central Pb+Pb/Au+Au events from AGS energies on (Elab = 4 AGeV) up to the highest RHIC energy available (V sNN = 200 GeV) and as a function of time with a set of central Au+Au qMD events at V sNN = 200 GeV with and without applying our hadronization procedure. For all studied quantities, the results start from values compatible with a weakly coupled QGP in the early stage and end with values compatible with the hadronic result in the final state. We show that the loss of the signal occurs at the same time as hadronization and trace it back to the dynamical recombination process implemented in our model.
The multiplicity of hadronic species created in elementary, and in nucleus-nucleus collisions, are known to be well reproduced by the statistical hadronization model, in its canonical and grand-canonical versions.To understand the origin of the implied equilibrium we revisit the hadronization models developed for e+e- annihilation to hadrons which imply spatial color pre-confinement clusters forming at the end of the pQCD evolution, which decays into on-shell hadrons/resonances. The classical ensemble description arises as a consequence of decoherence and phase space dominance during cluster formation, and decay.For A+A collisions we assume that hadronization occurs from similar singlet clusters which will overlap spatially owing to the extreme density. This is imaged in the transition to the grand-canonical ensemble.This transition sets in with increasing A and collision centrality. It can be described by a percolation model.
The strong nuclear force is described by Quantum Chromodynamics (QCD), the parallel field theory to Quantum Electrodynamics (QED) that describes the electromagnetic force. It is propagated by gluons analogously to photons in the electromagnetic force, but unlike photons, which do not carry electric charge, gluons carry color, and they can self-interact. However, as individual quarks have never been observed in nature, it is postulated that the color charge itself is confined, and hence all baryons and mesons must be colorless objects. To study nuclear matter under extreme conditions, it is necessary to create hot and dense nuclear matter in the laboratory. In such conditions the confinement between quarks and gluons is cancelled (deconfinement). This state is characterized with a qusi-free behavior of quarks and gluons. The strange (s) and anti-strange (anti-s) quarks are not contained in the colliding nuclei, but are newly produced and show up in the strange hadrons in the final state. It was suggested that strange particle production is enhanced in the QGP with respect to that in a hadron gas. This enhancement is relative to a collision where a transition to a QGP phase does not take place, such as p+p collisions where the system size is very small. Therefore the energy- and system size dependence is studied to receive a picture about the initial state. In this thesis experimental results on the energy- and system size dependence of Xi hyperon production at the CERN SPS is shown. All measurements were performed with the NA49 detector at the CERN SPS. NA49 took central lead-lead collisions from 20 - 158 AGeV, minimus bias lead-lead collisions at 40 and 158 AGeV, and semi-central silicon-silicon colisions at 158 AGeV. The NA49 experiment features a large acceptance in the forward hemisphere allowing for measurements of Xi rapidity spectra. At the SPS accelerator at CERN Pb+Pb collisions are performed with beam energies to 158 AGeV. The analyzed data sets were taken in the period from 1999 to 2002. The NA49 experiment is a large acceptance hadron spectrometer, which measures charged hadrons in a wide acceptance. The main components are the four TPCs (Time Projection Chamber). The centrality of nucleon-nucleon collisions was done by measuring the not in the collision participating (spectator-) nucleons in the VETO-calorimeter. The study of strangeness is motivated by its role as a signature for the Quark Gluon Plasma. Any enhancement in the yield must be with respect to a ’normal’ yield, where a QGP is not formed. This is usually taken to mean suitably scaled p+p collisions, where the volume of the system created is too small for a QGP to occur. The results at SPS and RHIC energies show an enhancement, with the doubly strange Xi? being enhanced more than the Lambda, in accordance with the original prediction. However, the enhancement at SPS energies is higher than at RHIC energies.