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HK: Hadronen und Kerne

HK 20: Structure of Baryons, Mesons III, Theory

HK 20.4: Group Report

Monday, March 16, 1998, 18:00–18:30, H

Pion-pion scattering in the rho-meson channel at finite temperature — •Yongbin He, J. Hüfner, S.P. Klevansky, and P. Rehberg — Institut für Theoretische Physik, Universität Heildelberg, Philosophenweg 19, 69120 Heidleberg

We study ππ scattering in the I=1, J^P=1⁻ channel at finite temperature in the framework of the extended Nambu-Jona-Lasinio model that explicitly includes vector and axial-vector degrees of freedom in addition to the usual scalar and pseudoscalar sector. The S-matrix in the coupled channels qq and π π is constructed via ρ-exchange in the s-channel. The self-energy of the ρ-meson contains both quark and pion loop contributions. The analytic structure of the S-matrix for T≥ 0 is investigated and the motion of the ρ-pole as a function of coupling constant and temperature is followed in the complex √s-plane. For numerical calculations, parameters are chosen in order that m_π, f_π and the experimental ππ phase shifts δ₁¹ at zero temperature are reproduced, and then the behavior of the ρ-pole as well as the ππ cross section is investigated as a function of the temperature. We find that the position of the ρ mass stays practically constant for 0≤ T≤ 150 MeV, and then moves down in energy by about 200 MeV for 150 MeV≤ T≤ 230 MeV.