The $ρ$-resonance with physical pion mass from $N_f=2$ lattice QCD

Abstract: We present the first-ever lattice computation of pi pi-scattering in the I=1 channel with Nf=2 dynamical quark flavours obtained including an ensemble with physical value of the pion mass. Employing a global fit to data at three values of the pion mass, we determine the universal parameters of the rho-resonance. We carefully investigate systematic uncertainties by determining energy eigenvalues using different methods and by comparing inverse amplitude method and Breit-Wigner type parametrizations. Overall, we find mass 786(20) MeV and width 180(6) MeV, including statistical and systematic uncertainties. In stark disagreement with the previous Nf=2 extrapolations from higher than physical pion mass results, our mass value is in good agreement with experiment, while the width is slightly too high.