IN-MEDIUM OMEGA-MESON BROADENING AND S-WAVE PION ANNIHILATION INTO E(-) PAIRS()E()

An omega-meson in motion with respect to a nuclear medium can couple t o a sigma-meson through a particle-hole excitation. This coupling is l arge. We investigate its consequences for the width of omega-mesons in matter and for the s-wave annihilation of pions into lepton pairs whi ch can take place in relativistic heavy ion collisions. We find that t he two pion decay of omega-mesons, resulting from the omega-sigma tran sition and the subsequent 2 pi decay of the sigma-meson, leads to a su bstantial broadening of omega-mesons in matter and possibly to an obse rvable effect in experiments measuring the e(+)e(-) decay of vector me sons produced in nuclei and in relativistic heavy-ion collisions. The inverse process, the s-wave annihilation of pions into omega-mesons de caying into e(+)e(-) pairs, has in general a much smaller cross sectio n than the corresponding p-wave annihilation through rho-mesons and is expected to contribute rather little to the total e(+)e(-) pair produ ction in relativistic heavy ion collisions. (C) 1998 Elsevier Science B.V.