Contact: Tom Parisi, NIU Office of Public Affairs
June 9, 2004
DeKalb, Ill. — A dozen Northern Illinois University physicists are part of a large team of scientists from Fermi National Accelerator Laboratory announcing a more precise measurement of the top quark, a subatomic particle discovered at the Batavia laboratory in 1995.
The team is publishing its results in Thursday's issue (June 10) of the prestigious British journal, Nature.
Using the new top-quark measurement, the researchers also have altered their best estimate for the mass of the Higgs boson, a mysterious and yet-to-be discovered particle that would help explain why objects have mass. Discovery of the Higgs is considered among the most sought-after prizes in the field of particle physics.
"The newly computed and more accurate mass of the top quark adds the latest wrinkle to the promising and exciting search for the Higgs boson at current and future particle accelerators," said Gerald C. Blazey, an NIU physicist who is co-spokesperson of the DZero collaboration at Fermilab. Blazey is among the more than 300 DZero scientists presenting their findings in Nature.
"If the Higgs boson does indeed exist, we have an improved idea of where it lives," Blazey said. "Finding the Higgs would confirm that the course of particle physics over the past four decades continues on the right track."
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 massless particles would populate the universe.
Previous estimates of the mass of the Higgs boson based on the Standard Model seemed inconsistent with data collected from particle physics experiments in recent years. When the new and more accurate mass of the top quark is factored into the equation, however, the inconsistencies largely disappear.
The top quark is the heaviest known elementary particle. The tiny particle exists for only a miniscule moment in time (10-24 seconds) but is linked to the Higgs boson.
While scientists have never observed the Higgs boson, they can predict its mass and other characteristics by making precise observations of known particles with which it presumably interacts. In particular, the masses of the top quark and the W boson together can be used to compute the mass of the Higgs. A precise measurement of the top-quark mass not only lets experimenters sharpen the search for the Higgs but also reveals whether the boson's existence is consistent with other experimental data.
The DZero collaboration now estimates the best value for the mass of the theorized Higgs boson at 117 GeV/c2. This is a higher mass than was previously inferred (96 GeV/c2) and is in better agreement with experimental results obtained at the European physics laboratory CERN that indicated the mass is above 114 GeV/c2.
The DZero collaboration brings together the expertise of more than 600 researchers. Scientists from nearly 40 U.S. universities and 40 foreign institutions contributed to the new measurement for the mass of the top quark. DZero physicists arrived at the measurement by applying a new analysis technique to data obtained from 1992 to 1996 at Fermilab's Tevatron, the world's highest-energy particle accelerator.
The new mass for the top quark will have implications in other areas of particle physics as well, according to Blazey. "Supersymmetric theories of particle physics depend on the properties of the Higgs, and these theories will be informed by our new measurement," he said.
Other NIU members of the team (including visiting professors and research scientists) listed on the Nature paper are Dhiman Chakraborty, Mary Anne Cummings, Alexandre Dyshkant, Michael Fortner, David Hedin, Jose Lima, Arthur Maciel, Manuel Martin, Daniel Mihalcea, Suzanne Willis and Vishnu Zutshi.
For more information on the Nature article, visit Fermilab online at www.fnal.gov.