String breaking by light and strange quarks in QCD

The energy spectrum of a system containing a static quark anti-quark pair is computed for a wide range of source separations using lattice QCD with N-f = 2 + 1 dynamical flavours. By employing a variational method with a basis including operators resembling both the gluon string and systems of two separated static mesons, the first three energy levels are determined up to and beyond the distance where it is energetically favourable for the vacuum to screen the static sources through light- or strange-quark pair creation, enabling both these screening phenomena to be observed. The separation dependence of the energy spectrum is reliably parameterised over this saturation region with a simple model which can be used as input for subsequent investigations of quarkonia above threshold and heavy-light and heavy-strange coupled-channel meson scattering. (C) 2019 The Authors. Published by Elsevier B.V.