arXiv subjects

Ulrich Mosel

Publications and source records attributed to Ulrich Mosel.

69 records · Page 4Linked to original sources

arXiv2003

Hadrons in Nuclei

Changes of hadronic properties in dense nuclear matter as predicted by theory have usually been investigated by means of relativistic heavy-ion reactions. In this talk I show that observable consequences of such changes can also be seen in more elementary reactions on nuclei. Particular emphasis is put on a discussion of photonuclear reactions; examples are the dilepton production at $\approx 1$ GeV and the hadron production in nuclei at 10 - 20 GeV photon energies. The observable effects are expected to be as large as in relativistic heavy-ion collisions and can be more directly related to the underlying hadronic changes.

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arXiv2003

Hadrons in Nuclei

Changes of hadronic properties in dense nuclear matter as predicted by theory have usually been investigated by means of relativistic heavy-ion reactions. In this talk I show that observable consequences of such changes can also be seen in more elementary reactions on nuclei. Particular emphasis is put on a discussion of photonuclear reactions; examples are the dilepton production at $\approx 1$ GeV and the hadron production in nuclei at 10 - 20 GeV virtual photon energies. The observable effects are expected to be as large as in relativistic heavy-ion collisions and can be more directly related to the underlying hadronic changes.

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arXiv2003

Short-Range Correlations in Nuclear Matter at Finite Temperatures and High Densities

The density and temperature dependence of nucleonic single particle spectral function in symmetric nuclear matter at finite temperatures and densities beyond normal nuclear matter density is investigated in a model emphasizing short-range correlations and phase space aspects. A simple but self-consistent approach based on quantum transport theory is used. In particular we consider the density and temperature regime occuring e.g. during the core collapse in a supernova explosion and the subsequent formation of a neutron star. Mean-field effects are incorporated by a Skyrme type potential.

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arXiv2003

Spectral Function of Quarks in Quark Matter

We investigate the spectral function of light quarks in infinite quark matter using a simple, albeit self-consistent model. The interactions between the quarks are described by the SU(2) Nambu--Jona-Lasinio model. Currently mean field effects are neglected and all calculations are performed in the chirally restored phase at zero temperature. Relations between correlation functions and collision rates are used to calculate the spectral function in an iterative process.

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arXiv2003

Chromofields of Strings and Baryons

We calculate color electric fields of quark/antiquark ($\bar{q}q$) and 3 quark ($qqq$) systems within the chromodielectric model (CDM). We explicitly evaluate the string tension of flux tubes in the $\bar{q}q$--system and analyze their profile. To reproduce results of lattice calculations we use a bag pressure $B = (320 MeV)^4$ from which an effective strong coupling constant $α_s \approx 0.3$ follows. With these parameters we get a $Y$ shaped configuration for large $qqq$--systems.

hep-ph↗

arXiv2002

Spectral Functions of Quarks in Quark Matter

We present a simple albeit self-consistent approach to the spectral function of light quarks in infinite quark matter. Relations between correlation functions and collision rates are used to calculate the spectral function in an iterative procedure. The quark interactions are described by the SU(2) Nambu--Jona-Lasinio model. Calculations were performed in the chirally restored phase at zero temperature.

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arXiv2000

Shadowing and Fragmentation in High-Energy Photo-Mesonproduction

A model for the description of photonuclear reactions in the multi-GeV range is described that combines the coherent initial state interactions (shadowing) of the incoming photon with an incoherent coupled channel description of final state interactons of outgoing particles. Particle production itself is treated either, at low energies, through nucleon resonance decays or, at higher energies, through string fragmentation. The initial state nucleons can be far-off-shell due to ground state correlations. Results are shown for semi-inclusive meson production.

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arXiv1999

Dilepton Production from Rho-Mesons in a Quark-Gluon Plasma

Assuming that rho-mesons exist in a quark-gluon plasma close to the QCD phase transition, we calculate the dilepton production rate from quark-antiquark annihilation via a rho-meson state using Vector Meson Dominance. The result is compared to the rates from direct quark-antiquark annihilation and from pion annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma.

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arXiv1998

Hadrons in the Nuclear Medium

In this talk I first discuss predictions based on QCD sum rules and on hadronic models for the properties of vector mesons in the nuclear medium. I then describe possible experimental signatures and show detailed predictions for dilepton invariant mass spectra with a special emphasis on nuclear reactions involving elementary incoming beams and nuclear targets. I will in particular illustrate that the sensitivity of pion and photon induced reactions to in-medium effects is nearly as large as that of heavy-ion reactions.

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arXiv1998

On QCD sum rules for vector mesons in nuclear medium

Vector mesons show up in the electromagnetic current-current correlator. QCD sum rules provide a constraint on hadronic models for this correlator. This constraint is discussed for the case of finite nuclear density concerning the longitudinal as well as the transverse part of the current-current correlator at finite three-momentum.

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arXiv1998

Pion Electroproduction and Pion-induced Dileptonproduction on the Nucleon

By introducing electromagnetic formfactors in the spacelike region we extend an effective, gauge invariant Lagrangian model considering Born terms, baryon resonances up to 1.7 GeV and vector meson contributions (Rho, Omega) to calculate electroproduction of Pi-mesons. This model forms the basis for predictions of pion induced dilepton production on the nucleon. Therefore, the implemented formfactors are constructed in such a way that their analytic continuation into the timelike region is possible. It is shown that the seagull term and the N*(1520) resonance play a dominant role in the dilepton production.

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arXiv1997

What QCD sum rules tell about the rho meson

Using a simple parametrization of Breit-Wigner type for the hadronic side of the QCD sum rule for $ρ$ mesons in vacuum as well as in a nuclear medium we explore the range of values for the mass and the width of the $ρ$ meson which are compatible with the operator product expansion.

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arXiv1994

Analysis of Subthreshold Antiproton Production in p-Nucleus and Nucleus-Nucleus Collisions in the RBUU Approach

We calculate the subthreshold production of antiprotons in the Lorentz-covariant RBUU approach employing a weighted testparticle method to treat the antiproton propagation and absorption nonperturbatively. We find that the pbar differential cross sections are highly sensitive to the baryon and antiproton selfenergies in the dense baryonic environment. Adopting the baryon scalar and vector selfenergies from the empirical optical potential for proton-nucleus elastic scattering and from Dirac-Brueckner calculations at higher density rho > rho_0 we examine the differential pbar spectra as a function of the antiproton selfenergy. A detailed comparison with the available experimental data for p-nucleus and nucleus-nucleus reactions shows that the antiproton feels a moderately attractive mean-field at normal nuclear matter density rho_0 which is in line with a dispersive potential extracted from the free annihilation cross section.

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arXiv1993

Study of High Energy Heavy-Ion Collisions in a Relativistic BUU-Approach with Momentum-Dependent Mean-Fields

We introduce momentum-dependent scalar and vector fields into the Lorentz covariant relativistic BUU- (RBUU-) approach employing a polynomial ansatz for the relativistic nucleon-nucleon interaction. The momentum-dependent parametrizations are shown to be valid up to about 1 GeV/u for the empirical proton-nucleus optical potential. We perform numerical simulations for heavy-ion collisions within the RBUU-approach adopting momentum-dependent and momentum-independent mean-fields and calculate the transverse flow in and perpendicular to the reaction plane, the directivity distribution as well as subthreshold K+-production. By means of these observables we discuss the particular role of the momentum-dependent forces and their implications on the nuclear equation of state. We find that only a momentum-dependent parameter-set can explain the experimental data on the transverse flow in the reaction plane from 150 - 1000 MeV/u and the differential K+-production cross sections at 1 GeV/u at the same time.

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arXiv1993

Antiproton Production in p-Nucleus and Nucleus-Nucleus Collisions within a Relativistic Transport Approach

The production of antiprotons in proton-nucleus and nucleus-nucleus reactions is calculated within the relativistic BUU approach employing proper selfenergies for the baryons and antiprotons and treating the p-bar annihilation nonperturbatively. The differential cross section for the antiprotons is found to be very sensitive to the p-bar selfenergy adopted. A detailed comparison with the available experimental data for p-nucleus and nucleus-nucleus reactions shows that the antiproton feels a moderately attractive mean-field at normal nuclear matter density which is in line with a dispersive potential extracted from the free annihilation cross section.

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