pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho -> pi gamma* decays in nuclear medium

摘要

We calculate the medium modification of the pi-omega-rho vertex and analyzeits significance for the pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho ->pi gamma* decays in nuclear matter. We use a relativistic hadronic approach atzero temperature and in the leading-density limit, and consider decays ofparticles at rest with respect to the medium. It is shown that for the pi^0 ->gamma gamma* the effects of the Delta isobar cancel almost exactly the effectsof the nucleon ph excitations, such that the net medium effect is small. On thecontrary, for the decays omega -> pi^0 gamma* and rho -> pi gamma* we find asizeable increase of the partial widths at virtualities of the photon in therange 0.3-0.6 GeV. The effect has direct significance for the calculation ofdilepton yields from the Dalitz decays in relativistic heavy-ion collisions.