# Bonn 2010 – wissenschaftliches Programm

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# HK: Fachverband Physik der Hadronen und Kerne

## HK 50: Schwerionenkollisionen und QCD Phasen V

### HK 50.3: Vortrag

### Donnerstag, 18. März 2010, 17:00–17:15, HG I

**Covariant computation of ***e*^{+}*e*^{−}** production in nucleon-nucleon collisions at HADES energies** — •R. Shyam and U. Mosel — Institut für Theoretische Physik, Universität Giessen

We present the results of our calculations for the electron-positron production
cross sections in nucleon-nucleon (*NN*)collisions within a fully relativistic
and gauge-invariant framework [1]. The model is based on the meson-exchange
approximation for the *NN*-scattering amplitudes. The production diagrams
include contributions from *NN* bremsstrahlung as well as from the mechanism
of excitation, propagation, and radiative decay of Δ(1232), Δ(1600),
*N*^{*}(1440), *N*^{*}(1520) intermediate baryonic resonant states.

Our particular emphasis is on describing the data taken by the HADES collaboration
[2] for both *pp* and the deuteron induced quasi-free *pn* reactions at the beam
energy of 1.25 GeV. In the latter case the available energy in the center of mass
(CM) has been smeared to include neutron momentum distribution in the deuteron. In
this case contributions from the η Dalitz decay have also been included as the
corresponding CM energies get larger than the *NN*η production threshold
due to Fermi smearing.

[1] R. Shyam, and U. Mosel, Phys. Rev. C **67**, 065202 (2003),
Phys. Rev. C **79**, 065202 (2009)

[2] G. Agakishiev *et al.*, arXiv:0910:5875