Quark as Basic Particle May Be in Dispute

Scientists plumbing the innermost workings of the atom have tentative but disquieting evidence that could challenge accepted theories about the structure of matter on the smallest scale.

It is possible that quarks--the smallest known constituents of protons and neutrons--are not fundamental, indivisible particles, but may be made up of yet smaller entities of unknown nature, said researchers from the Collider Detector at Fermilab, a consortium working at the federally sponsored accelerator outside Chicago.

The team turned up nearly 1,200 observations during a year of experiments in which colliding particles were deflected or “scattered” in ways that apparently cannot be reconciled with the predictions of current particle-physics theory. But the odd trajectories and energy levels observed in the collisions might make sense if quarks were composed of tiny sub-units that could send matter flying off in unexpected ways.

Until alternative explanations or possible errors have been ruled out, the 450-member team reports in a paper submitted to the nation’s leading physics journal, Physical Review Letters, “any claim about the presence or absence of new physics is not defensible.”

It could be that small adjustments in current theory could account for the discrepancies. But it is not inconceivable, Fermilab noted Wednesday, that “the data are the first hint that the fundamental constituents of matter may not be fundamental after all.”

The Fermilab measurements were first reported by the journal Science. Last year, Fermilab teams finally confirmed existence of the only one of six quarks that had never been observed, called the top quark.