Reading Comprehension 052


Painstaking observations of a kind of subatomic dance suggest that the universe may contain a shadowy form of matter that has never been seen directly and is unexplained by standard physics theories, a team of scientists working at Brookhaven National Laboratory on Long Island announced yesterday. The studies appear to confirm similar findings the scientists reported last year. The research involves muons, rare subatomic particles similar to electrons but 207 times as heavy.
The work has been controversial, though for reasons that have little to do with the experiment itself. Theorists who are not involved in the research, but whose computational results must be used to interpret it, have recently uncovered errors and uncertainties in their own work. For that reason, the Brookhaven experimenters say they are not ready to claim they have proved a new form of matter exists.

In a weird reflection of the boundless complexity of modern physics, top theorists from around the world were still sending conflicting calculations to the Brookhaven team in the hours before the new findings were disclosed yesterday afternoon at the laboratory. Frustration with the theorists boiled over at the lab, where scientists have been hoping that more than a year of new work would determine whether they had stumbled upon what would be a history-making discovery. The frustration stems from the seeming inability of the theorists to reach a solid conclusion. ''We're telling them, 'Look, you guys, get the damn answer on the table,' '' said Dr. Thomas B. Kirk, Brookhaven's associate director for high energy and nuclear physics.

The researchers found that muons wobbled like microscopic tops, or perhaps frenetic dancers, about 229,074 times a second, when they were placed in a powerful magnetic field in a vacuum chamber. Physicists have long known that such vacuums are not really empty, but are filled with a sea of ''virtual'' particles that flit briefly into existence and back into nothingness again. Like dance partners, the virtual particles change the rate at which the muons wobble. Theoretical physicists have long labored to calculate how much the rate of wobble, or precession, changes as a result of all the known particles in the virtual sea. Using those calculations, the Brookhaven researchers found last year -- and confirmed with the newer studies, involving observations of four billion muons -- that the actual wobble is about 0.6 times a second faster than predicted. The difference, called an anomaly by physicists, means the universe must contain previously undiscovered particles.

''If that sea contains some particles we didn't know about before, that will modify the anomaly,'' said Dr. James Miller, a professor of physics at Boston University -- one of 11 institutions in the United States, Russia, Japan and Germany involved in the experiment -- who presented the results yesterday. ''And the rate of precession is just directly proportional to that anomaly.'' Such a finding would delight many physicists who have been suggesting for years that the accepted theory, called the Standard Model, contains deep conceptual faults that can only be remedied with a more abstruse theory called supersymmetry. That theory predicts that every known particle has a difficult-to-detect partner that has yet to be discovered -- perhaps the extra particles in the virtual sea that the Brookhaven experiment may be detecting.

The initial Brookhaven finding was announced in February 2001. But a group of theorists in Marseille, France, announced in October that they had found a computational error in work led by another highly respected theorist, Dr. Toichiro Kinoshita of Cornell University, which was used to produce the Standard Model's prediction for the wobble. Dr. Kinoshita, who was traveling in Japan and unavailable for comment yesterday, acknowledged that a bug in his computer software had produced the error, said Dr. Sally Dawson, leader of the high-energy theory group at Brookhaven. A revised calculation found that the difference from the Standard Model's prediction, and therefore the evidence that new physics had been discovered, was ''much smaller than before,'' Dr. Dawson said.

That set off a worldwide scramble to refine the calculations further. So as the announcement approached yesterday, Dr. Lee Roberts, a physics professor at Boston University who is a spokesman for the Brookhaven experiment, was still sorting e-mail messages about new, conflicting calculations by theorists from Japan, Russia, Switzerland, England and France. ''Obviously, this is all work in progress,'' Dr. Roberts said. But all the new calculations showed at least some deviation from the Standard Model, he said. A few even suggested huge deviations, he added with a nervous chuckle. Meanwhile, the experimenters have a more immediate worry: the Bush administration has decided to end their financing after this year.


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Q1 Your answer was wrong for this question. The correct answer is: c

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Q4 Your answer was wrong for this question. The correct answer is: d

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