Quark mass and flavour dependence of the QCD phase transition

We analyze the quark mass and flavour dependence of the QCD phase transitio n temperature. When the lightest pseudo-scalar meson mass (m(PS)) is larger than 2 GeV the critical temperature is controlled by the gluonic sector of QCD alone. For smaller values of the lightest meson mass the pseudo-critic al temperature decreases slowly with mps. For a large regime of meson masse s the pseudo-critical temperature of 2-flavour QCD is about 10% larger than in the 3-flavour case. On lattices with temporal extent N-tau = 4 an extra polation to the chiral limit yields T-c = (173 +/- 8) MeV and (154 +/- 8) M eV for 2 and 3-flavour QCD, respectively. We also analyze dynamical quark m ass effects on the screening of the heavy quark potential. A detailed analy sis of the heavy quark free energy in 3-flavour QCD shows that close to T-c screening effects are approximately quark mass independent already for pse udo-scalar meson masses m(PS) less than or equal to 800 MeV and screening s ets in at distances r similar or equal to 0.3 fm. (C) 2001 Elsevier Science B.V. All rights reserved.