Asymmetric Quarks Defy Standard Model of Physics

News436-i0.1 Ron Cowen in Nature News:

Newly released observations of the top quark — the heaviest of all known fundamental particles — could topple the standard model of particle physics. Data from collisions at the Tevatron particle accelerator at Fermilab in Batavia, Illinois, hint that some of the top quark's interactions are governed by an as-yet unknown force, communicated by a hypothetical particle called the top gluon. The standard model does not allow for such a force or particle.

The results, presented1 today at the Europhysics Conference on High-Energy Physics in Grenoble, France, could help researchers to understand the origins of mass. According to one theoretical interpretation, a top quark bound by to its anti-matter partner, the antitop, would act as a version of the elusive Higgs boson, conferring mass on other particles.

Regina Demina, a physicist at the University of Rochester in New York, and her colleagues sifted through eight years' worth of particle-collision data recorded by one of the Tevatron's two detectors, known as DZero. Top quarks produced during collisions can fly off in the direction of the accelerator's proton beam or its antiproton beam; Demina and her team discovered that more travel towards the proton beam than is predicted in the standard model of physics. A different model would seem to be needed to explain the discrepancy.