Observation of new states decaying into ΛcK-π+ and Λc+KS0π-

We report the first observation of two charmed strange baryons that decay into Lambda K-+(c)-pi(+). The broader of the two states is measured to have a mass of 2978.5 +/- 2.1 +/- 2.0 MeV/c(2) and a width of 43.5 +/- 7.5 +/- 7.0 MeV/c(2). The mass and width of the narrow state are measured to be 3076.7 +/- 0.9 +/- 0.5 MeV/c(2) and 6.2 +/- 1.2 +/- 0.8 MeV/c(2), respectively. We also perform a search for the isospin partner states that decay into Lambda K-+(c)S(0)pi(-) and observe a significant signal at the mass of 3082.8 +/- 1.8 +/- 1.5 MeV/c(2). The data used for this analysis were accumulated at or near the Upsilon(4S) resonance, using the Belle detector at the e(+)e(-) asymmetric-energy collider KEKB. The integrated luminosity of the data sample used is 461.5 fb(-1).