Coupled channel analysis of theρmeson decay in lattice QCD

We employ a variational basis with a number of q̄q and ππ lattice interpolating fields with quantum numbers of the ρ resonance to extract the discrete energy spectrum in a finite volume. In the elastic region, this spectrum is related to the phase shift of the continuum scattering amplitude by L\"uscher's formula, and the relation allows the extraction of resonance parameters from the spectrum calculation. The simulations are performed at three different total momenta of the coupled q̄q-ππ system, which allows us to extract the p-wave scattering phase at five values of pion relative momenta near the resonance region. The effective range formula describes the phase-shift dependence nicely, and we extract the resonance mass m_ρ=792(7)(8) MeV and the coupling g_ρππ=5.13(20) at our m_π266 MeV. The coupling g_ρππ is directly related to the width of the ρ meson, and our value is close to the value derived from the experimental width. The simulations are performed using dynamical gauge configurations with two mass-degenerate flavors of tree-level improved clover-Wilson fermions. Correlation functions are calculated using the recently proposed distillation method with Laplacian-Heaviside smearing of quarks, which enables flexible calculations, in many cases with unprecedented accuracy.