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Monday, April 30, 2012

Scientists Confirm Existence of Excited Neutral Xi-b Baryon

The CERN physics research center said Friday that the particle was discovered at the Compact Muon Solenoid, one of the Large Hadron Collider's two main general-purpose detectors, in collaboration with the University of Zurich.

Joe Incandela, the physicist in charge of the experiment involved with the discovery, told The Associated Press that the particle was predicted long ago, but finding it was "really kind of a classic tour de force of experimental work."

The particle, known as an excited neutral Xi-b baryon, could not be detected directly because it was too unstable. Instead, its existence was inferred by the pattern of its decay into other subatomic particles.

The Xi-b particle, like other baryons such as protons and neutrons, is made up of three quarks. Protons and neutrons are combinations of "up" and "down" quarks (two up and one down for protons, two down and one up for neutrons). In contrast, the newly detected Xi-b particles consist of an up, strange and bottom quark. The particles are electrically neutral, with a spin of 3/2 and a mass comparable to that of a lithium atom, University of Zurich researchers said.

Xi-B baryons have been previously detected in their ground states, but the particles created in the LHC's proton-on-proton collisions are the first to be observed in their excited states. They're also the first newly discovered particles to be reported by the Compact Muon Solenoid collaboration, which takes in thousands of researchers.

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