D ec 2 01 2 Lattice investigation of the scalar mesons a 0 ( 980 ) and κ using four-quark operators

We carry out an exploratory study of the isospin one a0(980) and the isospin one-half κ scalar mesons using Nf = 2 + 1 + 1 Wilson twisted mass fermions at one lattice spacing. The valence strange quark is included as an Osterwalder-Seiler fermion with mass tuned so that the kaon mass matches the corresponding mass in the unitary Nf = 2+1+1 theory. We investigate the internal structure of these mesons by using a basis of four-quark interpolating fields. We construct diquark-diquark and molecular-type interpolating fields and analyse the resulting correlation matrices keeping only connected contributions. For both channels, the low-lying spectrum is found to be consistent with two-particle scattering states. Therefore, our analysis shows no evidence for an additional state that can be interpreted as either a tetraquark or a tightlybound molecular state.