Sigma meson production in proton-nucleus collisions

The sigma meson production is investigated in p + ⁴⁰Ca and p + ²⁰⁸Pb at the incident energy 1.5 GeV within the Quantum Molecular Dynamics model. The simulation results indicate a distinctive A dependence of the sigma production that the increase of A is followed by an increase of the production cross section. We find that the sigma meson production is strongly medium dependent and the produced sigma mesons decaying in a dense medium experience a stronger mass shift towards lower masses. This mass shift is an experimentally accessible observable in the final state pion pairs, which did not suffer absorption by the surrounding nucleons. It is pointed out that the ratio of measured sigma cross-sections as a function of the sigma invariant-mass from various reactions is a good probe to explore the existence of the sigma meson in dense nuclear environment. (author)