ρ⁰Production and possible modification in Au + Au and p + p collisions at √S_NN= 200 GeV

We report results on ρ(770)⁰ → π⁺ π^- production at midrapidity in p + p and peripheral Au + Au collisions at ps_NN = 200 GeV. This is the first direct measurement of ρ(770)⁰ → π⁺ π^- in heavy-ion collisions. The measured ρ⁰ peak in the invariant mass distribution is shifted by ∼40 MeV=c² in minimum bias p + p interactions and ∼70 MeV=c² in peripheral Au + Au collisions. The ρ⁰ mass shift is dependent on transverse momentum and multiplicity. The modification of the ρ⁰ meson mass, width, and shape due to phase space and dynamical effects are discussed.