Lattice QCD study of Ц- KN scattering and the (1405) resonance

A lattice QCD computation of the coupled channel NE- over bar KN scattering amplitudes in the A(1405) region is detailed. Results are obtained using a single ensemble of gauge field configurations with Nf = 2 + 1 dynamical quark flavors and mN approximate to 200 MeV and mK approximate to 487 MeV. Hermitian correlation matrices using both single baryon and meson -baryon interpolating operators for a variety of different total momenta and irreducible representations are used. Several parametrizations of the two -channel scattering K -matrix are utilized to obtain the scattering amplitudes from the finite -volume spectrum. The amplitudes, continued to the complex energy plane, exhibit a virtual bound state below the NE threshold and a resonance pole just below the over bar KN threshold.