Number 299 (Story #1), December 13, 1996 by Phillip F. Schewe and Ben Stein|
QUARKS ARE POINTLIKE AT THE 10**-19 METER LEVEL. Quarks, along with leptons, are the most elementary things in the universe, as far as experiments can tell. If quarks, which are the constituents of protons and neutrons, had constituents themselves, how would we know? One way is to smash quarks together and see what flies out. Physicists at Fermilab smash protons (which can be thought of as delivery vehicles for quarks) and antiprotons with one another and look at the outgoing jets of debris particles. Previously (Update 258) an excess of events with high-energy jets shooting away from the interaction at large angles was interpreted by some (although not by the experimentalists themselves) as possible evidence for subquarks. The latest word on the situation, as reported now by the CDF collaboration, is that quarks do not have any apparent structure. One way of expressing this is to say that if objects are hiding inside quarks, their energy would have to be greater than about 1.6 TeV. A still more dramatic way of registering this null result is to say that having trained their microscope on quarks, the Fermilab scientists see no objects at the 10**-19--meter level, the smallest distance scale inside quarks ever explored. (F. Abe et al. an article on dijet angular distribution in Physical Review Letters, 30 December 1996; contact Robert Harris at Fermilab, firstname.lastname@example.org; 630-840-4932.) A few other experiments, such as those that search for proton decay, have in effect probed even finer distance scales without finding any tiny lurking things.