High-speed collisions at a giant atom smasher have produced what physicists say is a new particle, a heavier relative of the familiar neutron.
The particle is called the neutral Xi-sub-b. When it's formed in the Fermilab Tevatron particle accelerator in Batavia, Ill., the neutral Xi-sub-b lasts just a mere instant before decaying into lighter particles. Scientists at Fermilab uncoverthese ephemeral particles by racing particles around a 4-mile (6.3 km) ring at near light speed. When the particles collide, the outpouring of energy disintegrates them into other particles.
Physics theory called the Standard Model predicted that the neutral Xi-sub-b should exist, but this is the first time researchers have seen it firsthand. The particle is a baryon, meaning it consists of three fundamental particles called quarks. Protons and neutrons, which make up the nucleus of atoms, are baryons. Protons contain two "up" quarks and one "down," while neutrons have two "down" quarks and an "up."