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NIU physicists help achieve quark-y milestone

by Tom Parisi

Scientists at Fermi National Accelerator Laboratory continue to close in on the Higgs boson, considered by some to be the holy grail of particle physics.

NIU physicists and advanced students are part of a large team of scientists at Fermilab announcing the first evidence of single top quarks produced in a rare subatomic process involving the weak nuclear force.

The DZero collaboration, an international experiment conducted by physicists from 90 institutions and 20 countries, announced the milestone in December.

The result is an important test of predictions made by particle theory, such as the number of quarks that exist in nature, according to Fermilab. In the longer term, the techniques employed in the analysis could assist scientists in the search for the Higgs boson.

The Standard Model of particle physics – the best explanation scientists have of the origins of the universe – predicts the existence of the Higgs boson. Its detection would confirm the existence of the Higgs field, which is thought to permeate the universe. When particles interact with this field, they gain mass. Without mass, all particles would travel at the speed of light, never sticking together, and only these tiny mass-less particles would populate the universe.

NIU physicists Gerald Blazey, David Hedin, Michael Fortner and Dhiman Chakraborty are members of the DZero collaboration, and about 10 graduate or post-doctoral students from NIU have worked on the experiment in recent years.

“Finding evidence of the single top quark and its characteristics is a very significant accomplishment in the world of particle physics. Not only is the measurement interesting in its own right, it represents a key precursor to finding the Higgs,” Blazey said. He served on the DZero editorial board at Fermilab that spent three months reviewing the analysis prior to the announcement.

“Other events resulting from particle collisions can masquerade as events with the Higgs, producing something akin to false positives, so it’s important for scientists to understand all the data,” he added. “Single top quarks are extremely rare in nature.”

Starting from a million billion proton-antiproton collisions produced by Fermilab’s Tevatron, the world’s most powerful particle collider, the DZero collaboration used modern sophisticated analysis techniques to search for about 60 collisions, each containing a single top quark.

Up to now, scientists had observed the top quark only in subatomic processes involving the strong nuclear force, which produces pairs of top and antitop quarks. Those observations, made by both the DZero and CDF experiments at Fermilab, led to the discovery of the top quark in 1995.