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Two new particles made of exotic types of quarks have appeared inside the Large Hadron Collider (LHC) near Geneva, Switzerland. The particles are never-before-seen species of baryons—a category of particles that also includes the familiar protons and neutrons inside atoms. The new baryons had been long predicted to exist, but their specific characteristics, such as their mass, were unknown until they were discovered in the flesh. The new measurements serve to confirm and refine the existing theory of subatomic particles and help pave the way for a deeper theory that could include even more exotic particles.

Scientists at the collider’s Large Hadron Collider beauty (LHCb) experiment reported the discovery of the baryons, called Xib'- and Xib*- (pronounced “zi-b-prime” and “zi-b-star”), February 10 in Physical Review Letters. (They posted a preprint of their paper in November on the arXiv server.) “These were two things that very much should have existed,” says Matthew Charles of Paris 6 University Pierre and Marie Curie, a co-author of the study. “Of course, you still have to check because every now and then you get a surprise.” Both particles contain one beauty, or b, quark, one strange quark and one down quark. What differentiates these particles from one another, and from one other conglomeration of the same three types of quarks that was previously found at the LHC, is the arrangement of the quarks' spins.

Quantum spin
Spin is one of the basic quantum characteristics intrinsic to any particle, and comes in unitless, discrete amounts. All quarks have a spin of one half. When two quarks inside the same particle are spinning in the same direction, their spins add together; when they rotate in opposite directions their spins cancel out. Spins are like magnets in that like repels like, so quarks prefer to spin in opposite directions. Extra energy is needed to align two quarks to spin in the same direction. The lowest-energy configuration of a Xib particle is for the two lightest quarks (the down and strange) to be antialigned, with their spins canceling out to zero, and the heavy b quark spinning in either direction, adding another one-half spin for a total spin of one half. That ground state, called Xib*0, was found at the LHC in 2012.

The two newfound baryons are higher-energy configurations. Both have the lightest two quarks spinning in parallel, adding to a combined spin of 1. Xib'- has its b quark spinning opposite those two, giving the particle a total spin of one half (from 1 minus one-half). In Xib* the spin of all three quarks is aligned, giving it a total spin of 1 and a half. This triple alignment requires the most energy of any configuration, causing Xib* to be the heaviest of the three states.

more:

http://www.scientificamerican.com/article/new-particles-found-at-large-hadron-collider/