An anomalous structure in S=−1 meson-baryon scattering in the resonance region

We present a simultaneous analysis of s- and p-waves of the S = −1 meson-baryon scattering amplitude using low-energy experimental data. For the first time differential cross section data are included for chiral unitary coupled-channel models. From this model s- and p-wave amplitudes are extracted and we observe both well-known I(J P ) = 0(1/2 −) s-wave states as well as a new I(J P ) = 1(1/2 +) state absent in quark models and lattice QCD results. Multiple statistical and phenomenological tests suggest that, while the data clearly require an I = 1 p-wave resonance, the new state accounts for the absence of the decuplet Σ(1385)3/2 + in the model.