Synopsis: Strange Beauty

A new baryon has been discovered by the CMS collaboration at the Large Hadron Collider.
Synopsis figure

One would think that by now, apart from big game like the Higgs boson, high-energy physicists would have bagged nearly all of the beasts on the particle horizon. There are still a few trophies to be taken, among them a group of baryons, each of which comprises one strange quark, one b quark (meaning bottom or beauty), and a third quark. When the third member of the trio is an up or down quark, the particle is known as a Ξb baryon. The Tevatron at Fermilab observed particle decays consistent with some of these states, but a full accounting was not available. Now, in a paper in Physical Review Letters, the CMS team at the Large Hadron Collider at CERN report their observation of a new particle that they conclude is likely to be the Ξb*0.

New particles are nearly always found by watching what they turn into, and the CMS collaboration observed a cascade of decays from Ξb*0 to Ξb- to J/ψ to muons, pions, and other bits and pieces. Careful reconstruction based on data from proton-proton events at the LHC puts the particle mass at 5945MeV, with a statistical significance of more than 5 standard deviations.

Nailing down further properties of the Ξb*0 remains a challenge, but the observation of a new member of the b-baryon family will help physicists understand how quarks interact in composite particles and shows that there is still room on the trophy wall for particle discoveries. – David Voss


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