ππ P-wave resonant scattering from lattice QCD

We present a high-statistics analysis of the ρ resonance in ππ scattering, using 2 + 1 flavors of clover fermions at a pion mass of approximately 320 MeV and a lattice size of approximately 3:6 fm. The computation of the two-point functions are carried out using combinations of forward, sequential, and stochastic propagators. For the extraction of the ρ-resonance parameters, we compare different fit methods and demonstrate their consistency. For the ππ scattering phase shift, we consider different Breit-Wigner parametrizations and also investigate possible nonresonant contributions. We find that the minimal Breit-Wigner model is suffcient to describe our data, and obtain am_ρ = 0:4609(16)_stat(14)_sys and g_ρππ = 5:69(13)_stat(16)_sys. In our comparison with other lattice QCD results, we consider the dimensionless ratios am_ρ/am_N and am_π/am_N to avoid scale setting ambiguities.