Lattice QCD Study of the σ Meson

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 “Asqtad” improved staggered fermion formulation. Particular attention is paid to its disconnected diagram and bubble contribution. After chiral extrapolation, we obtain the σ mass with 706±53 MeV, 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.