PARTICLE physicists at Fermilab near Chicago may have sighted the elusive "top" quark, one of the smallest constituents of matter (Science, Vol 258, No 5086; New Scientist, Vol 136, No 1851). An experiment at the Tevatron collider -a large particle smasher -yielded a pattern of particle debris that was anticipated when a bigger particle breaks down. When a proton and anti-proton collide, a top quark and an anti-top quark form and then decay into other particles.

The "top" is one of six types of quarks believed to exist and the only one left to be experimentally established. For this discovery to be confirmed, however, several other events must be observed and two groups at Fermilab are working towards this end.