Equation of State and the Finite Temperature Transition in QCD

This talk provides a summary of the results obtained by the HotQCD collaboration on the equation of state and the crossover transition in 2+1 flavor QCD. We investigate bulk thermodynamic quantities - energy density, pressure, entropy density, and the speed of sound over the temperature range 140 < T < 540 MeV. These results have been obtained on lattices of temporal size N_tau = 6 and 8 and with two improved staggered fermion actions, asqtad and p4. Our most extensive results are with masses of the two degenerate light quarks set at m_l = 0.1 m_s corresponding to the Goldstone pion mass m_pi between 220-260 MeV. In these simulations, the strange quark mass is tuned to its physical value and constant values of m_l/m_s define lines of constant physics. We also summarize the current state of results on observables sensitive to the chiral and deconfining physics -- the light and strange quark number susceptibilities, the chiral condensate and its susceptibility, and the renormalized Polyakov loop. Our results indicate that the deconfinement and chiral symmetry restoration occur in the same narrow temperature interval.