Zeroing in On a Weighty Enigma
One subatomic particle's mass gives hints about a still undiscovered prize
Tuesday, February 20, 2007
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Durham, NC -- American physicists have new hope that they can complete a scientific race to determine the masses of some extraordinarily elusive subatomic particles, thanks to key measurements by a Duke researcher.
Duke associate physics professor Ashutosh Kotwal and his colleagues have been using the high-energy particle accelerator at the Fermi National Accelerator Laboratory (Fermilab), near Chicago, to explain why almost all kinds of subatomic particles have mass.
"That's a key question in particle physics," Kotwal said. "That particles have masses is one of the key reasons that something like an atom can exist. And if an atom can exist, then molecules and DNA and, ultimately, life can exist."
But measuring the ephemeral subatomic particles is never easy. They must be created in atom smashers powerful enough to duplicate conditions microseconds after the "Big Bang," the moment when, physicists theorize, the universe was created in the ultimate cosmic fireball.
Early this year, Fermilab announced that a team led by Kotwal had pinned down the mass of a particle called the W boson, a subatomic particle that current theory says actuates the "weak force" responsible for radioactivity.
Measuring the W boson makes identification of another particle -- the mass-generating Higgs boson -- more likely. Knowing that the W boson acquires its mass by interacting with the Higgs field gives the researchers a way to infer the strength of the Higgs boson. Fields are mediums in which force-conveying bosons such as the Higgs and W are thought to operate. But the Higgs boson itself still awaits discovery.
The search for the Higgs boson "is like the quest for the gold at the end of the rainbow," said Kotwal, who also supervises computer analysis efforts at one of Fermilab's two huge detectors. "Measuring the W boson's mass is giving us an arrow to point toward the Higgs," he added.
What's even more encouraging about Kotwal's measurement is that it opens the possibility that Fermilab can discover the Higgs boson before the physics community redirects its efforts to the more powerful CERN Large Hadron Collider that will soon open near Geneva, Switzerland.
"Today, if we go to the high energy levels achievable at Fermilab, we are also able to produce real W bosons and measure their masses," Kotwal said. "We do so by measuring the energies of the particles that the W bosons decay into almost instantaneously."
For its latest achievement, Kotwal's team had to develop special software and perform extraordinarily precise and novel assessments within the approximately 8-foot by 9-foot, barrel-shaped wire chamber where such breakdown products are detected.
The fact that the new measurements show the W boson to be heavier than previously measured implies that the Higgs boson is lighter, and that insight gives physicists hope that Fermilab will be powerful enough to answer the question: how do particles acquire mass?
