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We study the σ meson in 2+1 flavor full quantum chromodynamics(QCD)with sufficiently light u and d quarks.The point-to-point correlator is measured for the σ channel in the"Asgtad"improved staggered fermion formulation.Particular attention is paid to its disconnected diagram and bubble contribution.After chiral extrapolation,we obtain the o mass with 706±53 Me V,which is close to the observed σ meson within error,and is heavier than the ππ threshold.The simulations are carried out with MILC 2+1 flavor gauge configurations at lattice spacing of a≈0.15 fm.