Charmed Baryons - Production and Detection

Production and Detection

Charmed baryons are formed in high-energy particle collisions, such as those produced by particle accelerators. The general method to find them is to detect their decay products, identify what particles they are, and measure their momenta. If all the decay products are found and measured correctly, then the mass of the parent particle may be calculated. As an example, a favored decay of the Λ+
c is into a proton, a kaon and a pion. The momenta of these (rather stable) particles are measured by the detector and using the usual rules of four-momentum using the correct relativistic equations, this gives a measure of the mass of the parent particle.

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. Thus, it is important to measure many such combinations. A plot of the calculated parent mass will then have a peak at the mass of the Λ+
c, but this is in addition to a smooth "phase space" background. 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. This makes the peak stand up less definitively against the background combinations. First observations of particles by this method are notoriously difficult – overzealous interpretation of statistical fluctuations or effects that produce false "peaks" mean that several published results were later found to be false. However, with more data collected by more experiments over the years, the spectroscopy of the charmed baryons states has now reached a mature level.