  We determine the curvature of the phase transition line in the mu-T plane
through an analysis of various observables, including the Polyakov loop, the
quark number susceptibilities and the susceptibility of the chiral condensate.
The second derivative of these quantities with respect to mu was calculated.
The measurements were carried out on N_T = 4,6,8 and 10 lattices generated with
a Symanzik improved gauge and stout-link improved 2+1 flavour staggered fermion
action using physical quark masses.
