arXiv subjects

U. Mosel

Publications and source records attributed to U. Mosel.

At least 91 records · Page 5Linked to original sources

arXiv2006

The spectral function of the omega meson in nuclear matter from a coupled-channel resonance model

We calculate the spectral function of the omega meson in nuclear matter at zero temperature by means of the low-density theorem. The omega N forward scattering amplitude is calculated within a unitary coupled-channel effective Lagrangian model that has been applied successfully to the combined analysis of pion- and photon-induced reactions. While the peak of the omega spectral distribution is shifted only slightly, we find a considerable broadening of the omega meson due to resonance-hole excitations. For omega mesons at rest with respect to the surrounding nuclear medium, we find an additional width of about 60 MeV at saturation density.

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arXiv2006

In-Medium Effects in Photo- and Neutrino-Induced Reactions on Nuclei

In this talk various aspects of in-medium behavior of hadrons are discussed with an emphasis on observable effects. It is stressed that final state interactions can have a major effect on observables and thus have to be considered as part of the theory. This is demonstrated with examples from photo-nucleus and neutrino-nucleus interactions.

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arXiv2006

Pion induced double charge exchange reactions in the Delta resonance region

We have applied the Giessen BUU (GiBUU) transport model to the description of the double charge exchange (DCX) reaction of pions with different nuclear targets at incident kinetic energies of 120-180 MeV . The DCX process is highly sensitive to details of the interactions of pions with the nuclear medium and, therefore, represents a major benchmark for any model of pion scattering off nuclei at low and intermediate energies. The impact of surface effects, such as the neutron skins of heavy nuclei, is investigated. The dependence of the total cross section on the nuclear mass number is also discussed. We achieve a good quantitative agreement with the extensive data set obtained at LAMPF. Furthermore, we compare the solutions of the transport equations obtained in the test-particle ansatz using two different schemes - the full and the parallel ensemble method.

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arXiv2006

Charged Current Neutrino Nucleus Interactions at Intermediate Energies

We have developed a model to describe the interactions of neutrinos with nucleons and nuclei, focusing on the region of the quasielastic and Delta(1232) peaks. We describe neutrino nucleon collisions with a fully relativistic formalism which incorporates state-of-the-art parametrizations of the form factors for both the nucleon and the N-Delta transition. The model has then been extended to finite nuclei, taking into account nuclear effects such as Fermi motion, Pauli blocking (both within the local density approximation), nuclear binding and final state interactions. The in-medium modification of the Delta resonance due to Pauli blocking and collisional broadening have also been included. Final state interactions are implemented by means of the Boltzmann-Uehling-Uhlenbeck (BUU) coupled-channel transport model. Results for charged current inclusive cross sections and exclusive channels as pion production and nucleon knockout are presented and discussed.

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arXiv2006

Prediction for the transverse momentum distribution of Drell-Yan dileptons at GSI-PANDA

We predict the triple differential cross section of the Drell-Yan process (pbar p -> l^+l^-X) in the kinematical regimes relevant for the upcoming PANDA experiment, using a model that accounts for quark virtuality as well as primordial transverse momentum. We find a cross section magnitude of up to 10 nb in the low mass region. A measurement with 10% accuracy is desirable in order to constrain the partonic transverse momentum dispersion and the spectral function width within +-50 MeV and to study their evolution with M and sqrt(s).

hep-ph↗

arXiv2006

Omega attenuation in nuclei

We study inclusive omega photoproduction in nuclei and propose a measurement of the nuclear transparency ratio as a means to learn about the in-medium properties of the omega meson. To this end we are using the semi-classical coupled-channel BUU transport approach that allows for a consistent treatment of all nuclear effects. The conditions of our calculations are chosen such as to match the setup of existing experimental facilities at ELSA or MAMI C. We show that the observables (total production cross section and transparency) indeed are sensitive to the omega N interaction in the nuclear medium.

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arXiv2006

Neutrino interactions with nucleons and nuclei at intermediate energies

We investigate neutrino-nucleus collisions at intermediate energies incorporating quasielastic scattering and Delta(1232) excitation as elementary processes, together with Fermi motion, Pauli blocking and mean-field potentials in the nuclear medium. A full coupled-channel treatment of final state interactions is achieved with a semiclassical BUU transport model. Results for inclusive reactions and nucleon knockout are presented.

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arXiv2005

Hadronization in nuclear DIS and ultra-relativistic HIC

We present a transport theoretical analysis of hadron attenuation in deep inelastic lepton scattering (DIS) off complex nuclei in the kinematic regime of the HERMES experiment. The HERMES data indicate the presence of strong prehadronic final state interactions shortly after the elementary lepton-nucleon interaction. The contribution of such (pre-)hadronic final state interactions to the observed jet quenching in ultra-relaticistic heavy ion collisions (HIC) at RHIC is estimated under the assumption that a similar space-time picture for hadronization also holds in a hot hadronic medium. Our results show that an additional mechanism for jet quenching must be at work for most central collisions.

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arXiv2005

Meson Production on the Nucleon in the Giessen K-Matrix Approach

Meson production on the proton is described in a coupled channels K-matrix approach. Both hadronic and photonic scenarios are taken into account on the same theoretical footing. At tree-level the Born amplitudes are obtained from an effective Lagrangian with phenomenologically adjustable coupling constants. The spectral distributions, resonances and their width and the background contributions are obtained within the same approach, thus accounting properly for interference effects. Applications to omega- and associated strangeness production on the proton are discussed.

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arXiv2005

Modelling Nuclear Effects in Neutrino Scattering

We have developed a model to describe the interactions of neutrinos with nucleons and nuclei via charged and neutral currents, focusing on the region of the quasielastic and Delta(1232) peaks. For neutrino nucleon collisions a fully relativistic formalism is used. The extension to finite nuclei has been done in the framework of a coupled-channel BUU transport model where we have studied exclusive channels taking into account in-medium effects and final state interactions.

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arXiv2005

Attenuation of phi mesons in gamma A reactions

We present a theoretical analysis of inclusive photoproduction of phi mesons in nuclei. In particular the dependence of the total phi meson yield on the target mass number is investigated. The calculations are done using the semi-classical BUU transport approach that combines the initial state interaction of the incoming photon with the coupled-channel dynamics of the final state particles. The conditions of the calculations are chosen such as to match the set up of a recent experiment performed at SPring8/Osaka. Whereas the observables prove to be rather sensitive to the phi self energy in the medium, the attribution of deviations from the standard scenario to a particular in-medium effect seems to be impossible.

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arXiv2005

A relativistic two-nucleon model for $A(p,K^+){_Λ}B$ reaction

We investigate the $A(p,K^+){_Λ}B$ reaction within a covariant two nucleon model. We focus on amplitudes which are described by creation, propagation and decay into relevant channel of $N^*$(1650), $N^*$(1710), and $N^*$(1720) intermediate baryonic resonance states in the initial collision of the projectile nucleon with one of its target counterparts. This collision is modeled by the exchange of $π$ as well as $ρ$ and $ω$ mesons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Expressions for the reaction amplitudes are derived taking continuum particle wave functions in both distorted wave and plane wave approximations. Detailed numerical results are presented in the plane wave approximation; estimates of the effects of the initial and final state interactions are given in the eikonal approximation. Cross sections of 1 - 2 nb/sr at the peak positions, are obtained for favored transitions in case of heavier targets.

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arXiv2005

Hadron attenuation by (pre)hadronic FSI at HERMES

We investigate hadron production in deep inelastic lepton-nucleus scattering in the kinematic regime of the HERMES experiment. Our calculations are carried out in the framework of a BUU transport model which contains the Lund event generators PYTHIA and FRITIOF for the simulation of high-energy elementary interactions. For the first time we consistently use the complete four-dimensional information of the Lund string break up vertices as input for our transport theoretical studies of (pre)hadronic final state interactions. We compare our results with experimental HERMES data on charged hadron attenuation.

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arXiv2005

Short Range Correlations and Spectral Functions in Asymmetric Nuclear Matter

Dynamical correlations in asymmetric infinite nuclear matter are investigates in a transport theoretical approach. Self-energies due to short range correlations and their influence on the nucleon spectral functions are described in an approach accounting for a realistic treatment of mean-field dynamics and a self-consistently derived quasi-particle interaction. Landau-Migdal theory is used to derived the short range interaction from a phenomenological Skyrme energy density functional. The spectral functions in asymmetric nuclear matter are found to follow in their gross features closely the patterns observed previously in symmetric nuclear matter. An interesting sensitivity of dynamical self-energies and spectral functions on the momentum structure of the underlying interactions is found.

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arXiv2005

Hadrons in Medium

After a short motivation I outline a consistent treatment of hadronic spectral functions based on transport theory. As examples I discuss nucleon spectral functions and the observable effects of changes of the properties of vector mesons inside nuclei.

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arXiv2005

Modelling Drell-Yan pair production in pbar-p

We predict the triple differential cross section of the unpolarized Drell-Yan process at sqrt(S)=6 GeV. The model incorporates primordial parton transverse momentum and quark off-shellness effects caused by the initial state interaction.

hep-ph↗

arXiv2005

Coupled-channel analysis of the $ω$-meson production in $πN$ and $γN$ reactions for c.m. energies up to 2 GeV

The pion- and photon induced reactions for the final states $γN$, $πN$, $2πN$, $ηN$, and $ωN$ are studied within a coupled-channel effective Lagrangian approach in the energy region from the pion threshold up to 2 GeV. To investigate the role of the nucleon resonances in the different reactions we include all known states with spin-$\foh$,-$\fth$, and -$\ffh$ and masses below 2 GeV. We find a strong contribution from the $D_{15}(1675)$ resonance to the $πN \to ωN$ reaction. While the $F_{15}(1680)$ state only slightly influences the $ω$ meson production in the $πN$ scattering its role is enhanced in the $ω$ photoproduction due to the large electromagnetic coupling of this resonance. We predict the beam asymmetry $Σ_X$ to be a negative in the $γp \to ωp$ reaction near to the threshold. Above the 1.85 GeV the asymmetry is found to change its sign and becomes positive at forward directions. The presented findings can be experimentally tested at GRAAL, CLAS, and CB-ELSA facilities.

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arXiv2005

Kaon production and propagation at intermediate relativistic energies

We systematically study $K^+$ observables in nucleus-nucleus collisions at 1-2 A GeV within the Boltzmann-Uehling-Uhlenbeck (BUU) transport model. We compare our calculations with the KaoS data on the kaon multiplicities and spectra. In addition, the kaon collective flow is computed and compared with the FOPI and KaoS data. We show, that the elliptic kaon flow measured recently by the KaoS Collaboration is best described by using the Brown-Rho parametrization of the kaon potential ($U_K(ρ_0) \simeq 30$ MeV).

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