Role of the strange quark in the ρ(770) meson

Abstract

Recently, the GWU lattice group has evaluated high-precision phase-shift data for ππ scattering in the I = 1, J = 1 channel. Unitary Chiral Perturbation Theory describes these data well around the resonance region and for different pion masses. Moreover, it allows to extrapolate to the physical point and estimate the effect of the missing KK̄ channel in the two-flavor lattice calculation. The absence of the strange quark in the lattice data leads to a lower ρ mass, and the analysis with UχPT shows that the KK̄ channel indeed pushes the ππ-scattering phase shift upward, having a surprisingly large effect on the ρ-mass. The inelasticity is shown to be compatible with the experimental data. The analysis is then extended to all available two-flavor lattice simulations and similar mass shifts are observed. Chiral extrapolations of Nf = 2 + 1 lattice simulations for the ρ(770) are also reported.