Exploring S-wave threshold effects in QCD: A heavy-light approach

Abstract

QCD exhibits complex dynamics near S-wave two-body thresholds. For light mesons, we see this in the failure of quark models to explain the f0(500) and K0⁎(700) masses. For charmonium, an unexpected X(3872) state appears at the open charm threshold. In heavy-light systems, analogous threshold effects appear for the lowest JP=0+ and 1+ states in the Ds and Bs systems. Here we describe how lattice QCD can be used to understand these threshold dynamics by smoothly varying the strange-quark mass when studying the heavy-light systems. Small perturbations around the physical strange quark mass are used so to always remain near the physical QCD dynamics. This calculation is a straightforward extension of those already in the literature and can be undertaken by multiple lattice QCD collaborations with minimal computational cost.