The curvature of the pseudo-critical line in the QCD phase diagram from mesonic lattice correlation functions

In the QCD phase diagram, the dependence of the pseudo-critical temperature, $T_{\mathrm{p}\mathrm{c}}$, on the baryon chemical potential, ${\mu }_B$, is of fundamental interest. The variation of $T_{\mathrm{p}\mathrm{c}}$ with ${\mu }_B$ is normally captured by $\kappa$, the coefficient of the leading (quadratic) term of the polynomial expansion of $T_{\mathrm{p}\mathrm{c}}$ with ${\mu }_B$. In this work, we present the first calculation of $\kappa$ using hadronic quantities. Simulating $N_f=2+1$ flavours of Wilson fermions on {\sc Fastsum} ensembles, we calculate the $\mathcal{O}({\mu }_B^2)$ correction to mesonic correlation functions. By demanding degeneracy in the vector and axial-vector channels we obtain $T_{\mathrm{p}\mathrm{c}}({\mu }_B)$ and hence $\kappa$. While lacking a continuum extrapolation and being away from the physical point, our results are consistent with previous works using thermodynamic observables (renormalised chiral condensate, strange quark number susceptibility) from lattice QCD simulations with staggered fermions.