Top quark telescope looks for something new

DZero physicists use the behavior of the single top quark like a telescope to look for new physics beyond the Standard Model.

Cranking up the energy of colliding particles isn’t the only way to search for new physics. The Standard Model predicts very specific behavior from each particle that we’ve observed and strictly defines the ways those particles interact. Precision tests of that behavior allow us to probe for physics beyond the Standard Model.

In that search, top quarks are particularly interesting to study because their high mass may imply they have a special role in new physics. The rare production of single top quarks, which happens about half as often as top quark pairs are made, presents a unique opportunity for studies that might help us see new physics.

At the Tevatron, there are two major ways of producing a single top quark. Scientists at DZero recently analyzed the rate of production in both of these channels independently. Certain models of new physics would affect one production channel more than the other, so determining the independent rates of the channels puts constraints on these new models while simultaneously testing the prediction of the Standard Model. In the end, this analysis has produced the most precise measurement of the larger single top quark production channel. The scientists also found a ratio of production rates that is consistent with the Standard Model.

Another recent analysis at DZero focuses on the way top quarks interact with W bosons. In nature, particle interactions can be different depending on the alignment of the intrinsic spins of the particles involved. We call such a preference handedness. The Standard Model predicts that W bosons only interact in a left-handed manner, which would lead to specific behavior in single top quark decay. DZero physicists tested whether single top quark decays were consistent with an exclusively left-handed W boson or if there were signs of either right-handed or more complicated couplings. Ultimately, they found that single top quark decays were consistent with the Standard Model and produced the most stringent constraints on anomalous couplings to date.

—Mike Cooke

These physicists, as part of the larger single top quark group at DZero, made major contributions to these analyses.
After nearly three years of authoring DZero’s Result of the Week articles, Don Lincoln (left) stepped down and Mike Cooke (right) took on the role.