Dilepton production in elementary and in heavy ion reactions

Abstract

We present a unified description of the vector meson and dilepton production in elementary and in heavy ion reactions. The production of vector mesons ($\rho ,\omega ,\varphi$) is described via the excitation of nucleon resonances ($R$). The theoretical framework is an extended vector meson dominance model (eVMD) for resonance decays $R⟼NV$ with arbitrary spin which is covariant and kinematically complete. The eVMD includes thereby excited vector meson states in the transition form factors. The model has successfully been applied to $\omega$ and $\varphi$ production in $p+p$ reactions. The same model is used to describe the dilepton production in elementary reactions where corresponding data are well reproduced. However, when the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the experimental dilepton spectra measured by the DLS Collaboration are significantly underestimated at small invariant masses. In view of this fact we discuss further medium effects: One is a substantial collisional broadening of the $\rho$ and in particular of the $\omega$ meson in the vicinity of the $\rho /\omega$-peak. The second medium effect is the destruction of quantum interference in a dense medium. A decoherent dilepton emission through vector mesons decays enhances the corresponding low mass dilepton yield in heavy ion reactions and improves the agreement with existing data.

14 pages, incl. 6 eps figures, invited talk presented at the 25th Course "Heavy Ion Reactions from Nuclear to Quark Matter", Erice, Sept. 16-24, 2003, to be publ. in Prog. Part. Nucl. Phys

References in corpus (5)

• Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV I: pion-induced results and hadronic parameters
• Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV II: photon-induced results
• Dilepton production in heavy ion collisions at intermediate energies
• Off-shell omega production in proton-proton collisions near threshold
• Exclusive $\varphi$ production in proton-proton collisions in the resonance model

Cited by in corpus (3)

• Dilepton production and off-shell transport dynamics at SIS energies
• Isospin dependent kaon and antikaon optical potentials in dense hadronic matter
• Pions valence quark distributions in asymmetric nuclear matter at finite temperature