[1] Since their first observation in the 1970s,[2] a large number of distinct charmed baryon states have been identified.
The general method to find them is to detect their decay products, identify what particles they are, and measure their momenta.
In particle collisions, the protons, kaons and pions are all rather commonly produced, and only a fraction of these combinations will have come from a charmed baryon.
The width of the peak will be governed by the resolution of the detector, provided that the charmed baryon is reasonably stable (such as the Λ+c which has a lifetime of around (2±10)×10−13 s).
Other, higher states of charmed baryons, which decay by the strong interaction, typically have large intrinsic widths.
However, with more data collected by more experiments over the years, the spectroscopy of the charmed baryons states has now reached a mature level.
It is not entirely clear when the particle was first observed; there were a number of experiments which published evidence for the state beginning in 1975, but the reported masses were frequently lower than the value now known.
This is a typical lifetime for particles that decay via the weak interaction, taking into account the large available phase space.
The decay into a proton, kaon and pion (each of them charged) is a favorite with experimenters as it is particularly easy to detect.
Studies of these branching ratios enable theoreticians to disentangle the various fundamental diagrams contributing the decays and is a window on weak interaction physics.
In Λ+c ground state, the two light quarks point up-down to give a zero spin diquark.
The intrinsic width of the Σc is small by the standard of most strong decays, but has now been measured, at least for the neutral and doubly charged states, to be around 2 MeV/c2 by the CLEO and FOCUS detectors.
These are clearly going to be "wider" because of the extra phase space of their decay, which like the Σc(2455) is to one pion plus a ground-state Λc.
Again, the neutral and doubly charged states are experimentally easier to detect, and these were discovered in 1997 by the CLEO Collaboration.
Not surprisingly, of the four weakly decaying, singly charmed baryons, the Ωc (the css quark combination), was the last to be discovered and the least-well measured.
Some authors claim that in 1985 a cluster of three events observed at CERN was a signal, but this can now be excluded on the grounds of its incorrect mass.
The CLEO experiment then showed a peak of 40 events in the sum of a variety of decay modes and a mass of 2494.6 MeV/c2.
Since then, two experiments, BaBar, and Belle, have taken a great deal of data, and have shown very strong signals at a mass very similar to the CLEO value.