The quark model, together with quantum mechanics predicts that there should be orbital excitations of Λ c particles. The lowest lying of these states are ones where the two light quarks (the up and down) combine into a spin-0 state, one unit of orbital angular momentum is added, and this combines with the intrinsic spin of the charm quark to make a ⁠ 1 / 2 ⁠, ⁠ 3 / 2 ⁠ pair of particles. The higher of these (the Λ c (2625)) was discovered in 1993 by ARGUS. At first it was not clear what state had been discovered, but the subsequent discovery of the lower state (2593) by CLEO clarified the situation. The decay modes, the masses, the measured widths, and the decays via two charged pions rather than one charged and one neutral pion, all confirm the identification of the states.