OPUS 4 | Search

Antibaryons in massive heavy ion reactions : importance of potentials (1995)

Christian Spieles Marcus Bleicher André Jahns Raffaele Mattiello Heinz Sorge Horst Stöcker Walter Greiner

In the framework of RQMD we investigate antiproton observables in massive heavy ion collisions at AGS energies and compare to preliminary results of the E878 collaboration. We focus here on the considerable influence of the real part of an antinucleon nucleus optical potential on the ¯p momentum spectra. Pacs-numbers: 14.20 Dh, 25.70.-z

Phasespace Correlations of Antideuterons in Heavy Ion Collisions (1995)

Marcus Bleicher Christian Spieles André Jahns Raffaele Mattiello Heinz Sorge Horst Stöcker Walter Greiner

In the framework of the relativistic quantum molecular dynamics approach (RQMD) we investigate antideuteron (d) observables in Au+Au collisions at 10.7 AGeV. The impact parameter dependence of the formation ratios d/p2 and d/p2 is calculated. In central collisions, the antideuteron formation ratio is predicted to be two orders of magnitude lower than the deuteron formation ratio. The d yield in central Au+Au collisions is one order of magnitude lower than in Si+Al collisions. In semicentral collisions di erent configuration space distributions of p s and d s lead to a large squeeze out e ect for antideuterons, which is not predicted for the p s.

Distillation of strangelets for low initial mu/T (1995)

Christian Spieles Carsten Greiner Horst Stöcker Jean Pierre Coffin

We calculate the evolution of quark-gluon-plasma droplets during the hadronization in a thermodynamical model. It is speculated that cooling as well as strangeness enrichment allow for the formation of strangelets even at very high initial entropy per baryon S/Ainit H 500 and low initial baryon numbers of Ainit B H 30. It is shown that the droplet with vanishing initial chemical potential of strange quarks and a very moderate chemical potential of up/down quarks immediately charges up with strangeness. Baryon densi- ties of H 2 0 and strange chemical potentials of µs > 350 MeV are reached if strangelets are stable. The importance of net baryon and net strangeness fluctuations for the possible strangelet formation at RHIC and LHC is em- phasized. Pacs-Classif.: 25.15.tr, 12.38.Mh, 24.85.tp

Hypermatter : properties and formation in relativistic nuclear collisions (1995)

Lars Gerland Christian Spieles Marcus Bleicher Panajotis Papazoglou Jörg Brachmann Adrian Dumitru Horst Stöcker Walter Greiner Jürgen Schaffner Carsten Greiner

The extension of the Periodic System into hitherto unexplored domains - anti- matter and hypermatter - is discussed. Starting from an analysis of hyperon and single hypernuclear properties we investigate the structure of multi-hyperon objects (MEMOs) using an extended relativistic meson field theory. These are contrasted with multi-strange quark states (strangelets). Their production mechanism is stud- ied for relativistic collisions of heavy ions from present day experiments at AGS and SPS to future opportunities at RHIC and LHC. It is pointed out that abso- lutely stable hypermatter is unlikely to be produced in heavy ion collisions. New attention should be focused on short lived metastable hyperclusters ( / 10 10s) and on intensity interferometry of multi-strange-baryon correlations.

Dynamics of strangeness production and strange matter formation (1996)

Christian Spieles Marcus Bleicher Lars Gerland Horst Stöcker Carsten Greiner

We want to draw the attention to the dynamics of a (finite) hadronizing quark matter drop. Strange and antistrange quarks do not hadronize at the same time for a baryon-rich system1. Both the hadronic and the quark matter phases enter the strange sector fs 6= 0 of the phase diagram almost immediately, which has up to now been neglected in almost all calculations of the time evolution of the system. Therefore it seems questionable, whether final particle yields reflect the actual thermodynamic properties of the system at a certain stage of the evolution. We put special interest on the possible formation of exotic states, namely strangelets (multistrange quark clusters). They may exist as (meta-)stable exotic isomers of nuclear matter 2. It was speculated that strange matter might exist also as metastable exotic multi-strange (baryonic) objects (MEMO s 3). The possible creation in heavy ion collisions of long-lived remnants of the quark-gluon-plasma, cooled and charged up with strangeness by the emission of pions and kaons, was proposed in 1,4,5. Strangelets can serve as signatures for the creation of a quark gluon plasma. Currently, both at the BNL-AGS and at the CERN-SPS experiments are carried out to search for MEMO s and strangelets, e. g. by the E864, E878 and the NA52 collaborations9,

Detectability of strange matter in heavy ion experiments (1996)

Jürgen Schaffner-Bielich Carsten Greiner Alexander Diener Horst Stöcker

We discuss the properties of two distinct forms of hypothetical strange matter, small lumps of strange quark matter (strangelets) and of hyperon matter (metastable exotic multihypernuclear objects: MEMOs), with special empha- sis on their relevance for present and future heavy ion experiments. The masses of small strangelets up to AB = 40 are calculated using the MIT bag model with shell mode filling for various bag parameters. The strangelets are checked for possible strong and weak hadronic decays, also taking into account multiple hadron decays. It is found that strangelets which are stable against strong decay are most likely highly negative charged, contrary to previous findings. Strangelets can be stable against weak hadronic decay but their masses and charges are still rather high. This has serious impact on the present high sensitivity searches in heavy ion experiments at the AGS and CERN facilities. On the other hand, highly charged MEMOs are predicted on the basis of an extended relativistic mean field model. Those objects could be detected in future experiments searching for short lived, rare composites. It is demonstrated that future experiments can be sensitive to a much wider variety of strangelets.

Hadron and hadron cluster production in a hydrodynamical model including particle evaporation (1997)

Adrian Dumitru Christian Spieles Horst Stöcker Carsten Greiner

We discuss the evolution of the mixed phase at RHIC and SPS within boostinvariant hydrodynamics. In addition to the hydrodynamical expansion, we also consider evaporation of particles o the surface of the fluid. The back-reaction of this evaporation process on the dynamics of the fluid shortens the lifetime of the mixed phase. In our model this lifetime of the mixed phase is d 12 fm/c in Au + Au at RHIC and d 6.5 fm/c in Pb + Pb at SPS, even in the limit of vanishing transverse expansion velocity. Strong separation of strangeness occurs, especially in events (or at rapidities) with relatively high initial net baryon and strangeness number, enhancing the multiplicity of MEMOs (multiply strange nuclear clusters). If antiquarks and antibaryons reach saturation in the course of the pure QGP or mixed phase, we find that at RHIC the ratio of antideuterons to deuterons may exceed 0.3 and even 4He/4He > 0.1. In S + Au at SPS we find only N/N H 0.1. Due to fluctuations, at RHIC even negative baryon number at midrapidity is possible in individual events, so that the antibaryon and antibaryon-cluster yields exceed those of the corresponding baryons and clusters.

Intermediate mass excess of dilepton production in heavy ion collisions at BEVALAC energies (1998)

Christoph Ernst Steffen A. Bass Mohamed Belkacem Horst Stöcker Walter Greiner

Dielectron mass spectra are examined for various nuclear reactions recently measured by the DLS collaboration. A detailed description is given of all dilepton channels included in the transport model UrQMD 1.0, i.e. Dalitz decays of π, η, ω, ή mesons and of the (1232) resonance, direct decays of vector mesons and pn bremsstrahlung. The microscopic calculations reproduce data for light systems fairly well, but tend to underestimate the data in pp at high energies and in pd at low energies. These conventional sources, however, cannot explain the recently reported enhancement for nucleus-nucleus collisions in the mass region 0.15GeV ≤ Me+e- ≤ 0.6GeV. Chiral scaling and ω meson broadening in the medium are investigated as a source of this mass excess. They also cannot explain the recent DLS data.

Dissociation rates of J / psi's with comoving mesons : thermal versus nonequilibrium scenario. (1998)

Christian Spieles Ramona Vogt Lars Gerland Steffen A. Bass Marcus Bleicher Horst Stöcker Walter Greiner

We study J/psi dissociation processes in hadronic environments. The validity of a thermal meson gas ansatz is tested by confronting it with an alternative, nonequilibrium scenario. Heavy ion collisions are simulated in the frame- work of the microscopic transport model UrQMD, taking into account the production of charmonium states through hard parton-parton interactions and subsequent rescattering with hadrons. The thermal gas and microscopic transport scenarios are shown to be very dissimilar. Estimates of J/psi survival probabilities based on thermal models of comover interactions in heavy ion collisions are therefore not reliable.

Signatures of quark gluon plasma formation in high-energy heavy ion collisions : a critical review (1998)

Steffen A. Bass Miklos Gyulassy Horst Stöcker Walter Greiner

Ultra-relativistic heavy ion collisions offer the unique opportunity to probe highly excited dense nuclear matter under controlled laboratory conditions. The compelling driving force for such studies is the expectation that an entirely new form of matter may be created from such reactions. That form of matter, called the Quark Gluon Plasma (QGP), is the QCD analogue of the plasma phase of ordinary atomic matter. However, unlike such ordinary plasmas, the deconfined quanta of a QGP are not directly observable because of the fundamental confining property of the physical QCD vacuum. What is observable are hadronic and leptonic residues of the transient QGP state. There is a large variety of such individual probes.

Refine

Author

Year of publication

Document Type

Keywords

11 search hits