ρ\u3csup\u3e0\u3c/sup\u3e production and possible modification in Au + Au and p + p collisions at √s\u3csub\u3eNN\u3c/sub\u3e = 200 GeV

We report results on ρ(770)0→π+π− production at midrapidity in p+p and peripheral Au+Au collisions at √sNN=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