The 1405MeV Lambda Resonance in Full-QCD

Abstract

The negative-parity ground state of the Λ baryon lies surprisingly low in mass. At 1405.1 MeV, it lies lower than the negative-parity ground state nucleon, even though it has a valence strange quark. Using the PACS-CS (2 + 1)-flavour full-QCD ensembles available through the ILDG, we employ a variational analysis using source and sink smearing to investigate the low-energy, odd-parity spectrum of the Λ baryon. We isolate two low-lying odd-parity states, with the lowest state approaching the Λ(1405) in the physical limit. Moreover, for the first time we reproduce the correct level ordering with respect to the nearby multiparticle scattering thresholds.