New subatomic particle observed for first time

Posted by Kate Taylor

Collision Detector at Fermilabs (CDF) scientists have observed a new particle, the neutral Xi-sub-b.

Predicted by the Standard Model but never before seen, the particle, a baryon, contains three quarks - a strange quark, an up quark and a bottom quark.

It's the newest baryon - a particle formed of three quarks - and is rare and very difficult to observe. It belongs to the family of bottom baryons, which are about six times heavier than the proton and neutron (also baryons) because they contain a heavy bottom quark.

Fermilab’s Tevatron particle collider has been used to discovered and studied almost all the known bottom baryons. It was responsible for finding the Sigma-sub-b baryons (Σb and Σb*) in 2006, observed the Xi-b-minus baryon (Ξb-) in 2007, and found the Omega-sub-b (Ωb-) in 2009. The lightest bottom baryon, the Lambda-sub-b (Λb), was discovered at CERN.

Measuring the properties of these particles allows scientists to test and improve models of how quarks interact at close distances via the strong nuclear force, as explained by the theory of quantum chromodynamics (QCD).

Once produced, the neutral Xi-sub-b travels only a fraction of a millimeter before decaying into lighter particles - which in turn decay into even lighter ones. Physicists rely on the details of this series of decays to identify the initial particle.

The complex decay pattern of the neutral Xi-sub-b has made it particularly hard to observe. Combing through almost 500 trillion proton-antiproton collisions produced by the Tevatron particle collider, the team isolated 25 cases in which the particles emerging from a collision revealed the distinctive signature of the neutral Xi-sub-b.