Determination of s- and p-wave I = 1/2 Kπ scattering amplitudes in Nf = 2 + 1 lattice QCD

The elastic I = 1 / 2 , s - and p -wave kaon-pion scattering amplitudes are calculated using a single ensemble of anisotropic lattice QCD gauge field configurations with N f = 2 + 1 flavors of dynamical Wilson-clover fermions at m π = 230 MeV . A large spatial extent of L = 3.7 fm enables a good energy resolution while partial wave mixing due to the reduced symmetries of the finite volume is treated explicitly. The p -wave amplitude is well described by a Breit–Wigner shape with parameters m K ⁎ / m π = 3.808 ( 18 ) and g K ⁎ K π BW = 5.33 ( 20 ) which are insensitive to the inclusion of d -wave mixing and variation of the s -wave parametrization. An effective range description of the near-threshold s -wave amplitude yields m π a 0 = − 0.353 ( 25 ) .