Physicists Confirm Existence of New Particle

Scientists of the CDF collaboration at the Department of Energy’s Fermi National Accelerator Laboratory announced the observation of a new particle, the neutral Xi-sub-b (Ξ_b⁰).

This particle contains three quarks: a strange quark, an up quark and a bottom quark (s-u-b). While its existence was predicted by the Standard Model, the observation of the neutral Xi-sub-b is significant because it strengthens our understanding of how quarks form matter. Fermilab physicist Pat Lukens, a member of the CDF collaboration, presented the discovery at Fermilab on Wednesday, July 20.

Six quarks–up, down, strange, charm, bottom and top–are the building blocks of matter.

The neutral Xi-sub-b is the latest entry in the periodic table of baryons. Baryons are particles formed of three quarks, the most common examples being the proton (two up quarks and a down quark) and the neutron (two down quarks and an up quark). The neutral Xi-sub-b belongs to the family of bottom baryons, which are about six times heavier than the proton and neutron because they all contain a heavy bottom quark. The particles are produced only in high-energy collisions, and are rare and very difficult to observe.

Although Fermilab’s Tevatron particle collider is not a dedicated bottom quark factory, sophisticated particle detectors and trillions of proton-antiproton collisions have made it a haven for discovering and studying almost all of the known bottom baryons. Experiments at the Tevatron discovered the Sigma-sub-b baryons (Σ_b and Σ_b*) in 2006, observed the Xi-b-minus baryon (Ξ_b^–) in 2007, and found the Omega-sub-b (Ω_b^–) in 2009. The lightest bottom baryon, the Lambda-sub-b (Λ_b), was discovered at CERN. Measuring the properties of all 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). Scientists at Fermilab and other DOE national laboratories use powerful computers to simulate quark interactions and understand the properties of particles comprised of quarks.