Curvature of the chiral pseudo-critical line in QCD: continuum extrapolated results

We determine the curvature of the pseudo-critical line of strong interactions by means of numerical simulations at imaginary chemical potentials. We consider $N_f=2+1$ stout improved staggered fermions with physical quark masses and the tree level Symanzik gauge action, and explore four different sets of lattice spacings, corresponding to $N_t = 6,8,10,12$, in order to extrapolate results to the continuum limit. Our final estimate is $\kappa = 0.0135(20)$.