QCD equation of state with 2+1 flavors of improved staggered quarks

We report results for the interaction measure, pressure, and energy density for nonzero-temperature QCD with 2 + 1 flavors of improved staggered quarks. In our simulations, we use a Symanzik improved gauge action and the Asqtad O(a2) improved staggered quark action for lattices with temporal extent Nt = 4 and 6. The heavy quark mass ms is fixed at approximately the physical strange quark mass and the two degenerate light quarks have masses mud ≈ 0:1ms or 0:2ms. The calculation of the thermodynamic observables employs the integral method where energy density and pressure are obtained by integration over the interaction measure.