As further particles were discovered, they were assigned into isospin multiplets according to the number of different charge states seen: 2 doublets I = ⁠ 1 / 2 ⁠ of K mesons (K, K), (K, K), a triplet I = 1 of Sigma baryons (Σ, Σ, Σ), a singlet I = 0 Lambda baryon (Λ), a quartet I = ⁠ 3 / 2 ⁠ Delta baryons (Δ, Δ, Δ, Δ), and so on.