In the standard quark model, Ξ c comprises a csu quark combination and the Ξ c comprises a csd quark combination. Both particles decay via the weak interaction. The first observation of the Ξ c was in 1983 by the WA62 collaboration working at CERN. They found a significant peak in the decay mode Λ K π π at a mass of 2460 ± 25 MeV/ c. The present value for the mass is taken from an average of 6 experiments, and is 2 467.9 ± 0.4 MeV/ c.