Thermodynamics of four-flavour QCD with improved staggered fermions

We have calculated the pressure and energy density in four-flavour QCD using improved fermion and gauge actions. We observe a strong reduction of finite cut-off effects in the high temperature regime, similar to what has been noted before for the SU(3) gauge theory. Calculations have been performed on 163 × 4 and 164 lattices for two values of the quark mass, ma = 0.05 and 0.1. A calculation of the string tension at zero temperature yields a critical temperature Tcσ=0.407±0.010 for the smaller quark mass value.