We report on our study of QCD thermodynamics with 2 ¡ 1 flavors of dynamical quarks. In this proceeding we present several thermodynamic quantities and our recent calculation of the critical temperature. In order to investigate the thermodynamic properties of QCD near the continuum limit we adopt improved staggered (p4) quarks coupled with tree-level Symanzik improved glue on N t
Introduction and Lattice SetupThe calculation of QCD thermodynamics from first principle is important for various research areas such as Heavy Ion Phenomenology, Cosmology and Astrophysics. Lattice QCD enables us to carry out such calculations. Especially for HIC phenomenology it is mandatory to improve estimates on some basic thermodynamic quantities which have been obtained in previous lattice calculations. One of the main subjects in our project is the accurate determination of the critical temperature T c , whose uncertainty, for example, strongly affects the critical energy density ε c because of its T c dependence, ε c¨T 4 c . Since thermodynamics of lattice QCD requires huge computational resources, it is difficult to perform an ideal simulation. Recent studies tell us that quark masses and the number of flavors strongly affect thermodynamic quantities [1]. Reliable continuum extrapolations are of tremendous importance as well [2]. Therefore, it is our aim to study QCD thermodynamics with almost realistic quark masses on the QCDOC machine at Brookhaven National Laboratory and the APEnext machine at Bielefeld University. The calculation is performed with N f © 2 1, which means 2 degenerate light quarks and one heavier quark on lattices with N t © 4 and 6. The lightest quark masses of our simulation yields a pion mass of about 150 MeV and a kaon mass of about 500 MeV.For such calculations we adopt the p4fat3 quark action, which is an improved Staggered quark action [3], with a tree-level improved Symanzik gauge action. By using the p4fat3 action, the free quark dispersion relation has the continuum form up to O p 4 , and the taste symmetry breaking is suppressed by a 3-link fattening term. The action also improves bulk thermodynamical quantities in the high temperature limit [3]. The improvements are essential to control the continuum extrapolation on rather coarse lattices, i.e. N t © 4 and 6. The gauge ensembles are generated by an exact RHMC algorithm [4].As a status report of the project, in this proceeding, we present several thermodynamic quantities, which are order parameters and their susceptibilities, the static quark potential, and the spatial string tension. In the last section we discuss the critical temperature at the physical point. The details of the critical temperature calculation are given in our recent paper [5].
Order Parameters and SusceptibilitiesTo investigate the QCD critical temperature and phase diagram, order parameters of the QCD transition are indispensable. In the chiral limit the chiral condensate ¯ψψ is the order parameter for the spontaneous chiral symmetry breaking of QCD. On the other hand in th...