Finite T/µ lattice QCD and the critical point

We present results on lattice QCD at finite temperature (T) and chemical potential (µ). We apply the overlap-improving multi-parameter reweighting technique for n f = 4 and 2 + 1 staggered QCD. We use semi-realistic masses on Lt=4 lattices. The critical endpoint (E) of 2+1 flavour QCD on the µ-T plane is located. Our results are based on O(10 3 − 10 4) configurations. §1. Introduction QCD at finite T and/or µ describes relevant features of particle physics in the early universe, in neutron stars and in heavy ion collisions. Extensive experimental work has been done with heavy ion collisions at CERN and Brookhaven to explore the µ-T phase boundary (cf. 1)). It is a long-standing question, whether a critical point exists on the µ-T plane, and particularly how to tell its location theoretically. 2) T µ E quark gluon plasma SC phase. . n =2+1 f hadronic phase Fig. 1. Schematic phase diagram of QCD in the µ − T plane. At µ = 0 and finite T a cross-over is expected. The endpoint (E) connects the cross-over region with the first-order region at large µ. Let us start with the µ=0 case first (see Fig. 1). Universality arguments 3) and