Bonn 2010 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 50: Schwerionenkollisionen und QCD Phasen V

HK 50.3: Talk

Thursday, March 18, 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 NNη 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