Bochum 1998 – scientific programme
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HK: Hadronen und Kerne
HK 54: Structure of Baryons, Mesons VII, Theory
HK 54.4: Group Report
Wednesday, March 18, 1998, 15:30–16:00, H
Rho-Meson Propagation in Hadronic Matter — •M. Buballa1, M. Urban1, R. Rapp2, Th. Roth1, and J. Wambach1 — 1Institut für Kernphysik, TU Darmstadt — 2Dept. of Physics, SUNY at Stony Brook, U.S.A.
Because of their close relation to electromagnetic processes the properties of vector mesons at finite densities or temperatures are of great interest. We present a new hadronic model for the ρ-meson in hadronic matter. We start from a vacuum model with a bare propagator dressed by ππ-loops. This gives a good description of the pion electromagnetic formfactor and the phase shifts for p-wave ππ-scattering. In matter we consider the renormalization of these pion loops through patricle-hole and Δ-hole excitations as well as rescattering processes of the ρ-meson in the medium. Special care is taken to preserve gauge invariance not only for the ρ-meson at rest but also at finite 3-momenta. This turns out to be important to shift part of the strength down to the regime of low invariant masses. The main effect can be attributed to the decay of the ρ into a pion and a transverse Δ-hole pair.
In order to further constrain the parameters we apply our model to the calculation of total photoabsorption cross sections in γ-proton and γ-nucleus reactions. We obtain a satisfactory description of the data up to ∼ 1 GeV. As an additional test we analyse the reaction π N → ρ N. Having the parameters fixed in this way, we calculate the dilepton spectra which have been measured in central heavy-ion collisions at CERN/SpS. Our results which are in reasonable agreement with the data are discussed in the light of competing models.