BY SUSAN LONKEVICH

Each morning Dr. Josh Klein shows up for work in miner’s garb—hard hat, safety boots, the works—and waits for the “cage,” or elevator, to take him down one and one-quarter miles into the Earth.
   “The cage is usually jam-packed,” says the 35-year-old Penn physicist, who has spent the better part of the past few years commuting down into a nickel mine in northern Ontario. “When you can put both feet on the floor, you’re pretty happy about it.” Around 3,000 feet, “Everybody’s working their jaws” to relieve the pressure on their ears. “If you have a head cold, it’s incredibly painful.”
   Next he walks 1.25 miles to a lab, where the first step is getting clean. “First you wash your boots off twice. Then you go in, take off your hard hat, belt, all your clothes, go through showers, put on new clean clothes, and you put on a hairnet.” That’s to keep the lab free of mine dust. As little as a thimble-full, says Klein, could produce misleading signals in a sensitive detector that, through the help of Penn scientists, has played a pivotal role in the hunt for solar neutrinos.
   If neutrinos were people, they’d be loners: the stranger who shows up at a party without so much as a bottle of Beaujolais for the host, talks to no one, and then mysteriously disappears out the back door into the night. Dr. Paul Langacker, Penn professor of physics, describes them as “oddballs” in the realm of subatomic particles. But, he says, “There’s more than meets the eye.” Neutrinos call to mind “somebody who at first glance is very quiet and unassuming, but is very deep and has a lot of consequences.”
    Thus it was with much fanfare in mid-June that scientists working at the Sudbury Neutrino Observatory (SNO) announced the results of the latest hunt for these tiny, elusive particles. With an elaborate detector sunk two kilometers below the surface in an active nickel mine in Sudbury, Ontario, the multinational team found direct proof that solar neutrinos, produced in fusion reactions at the center of the sun, are also quick-change artists: On their eight-minute journey to Earth, about two-thirds of solar neutrinos change into different types—or flavors, as physicists call them—that are more difficult to detect. This explains why for more than three decades, scientists have been unable to detect neutrinos at a rate consistent with the standard model of how our sun works. “Our latest result is the smoking gun, I would say,” says Dr. Eugene Beier, a Penn physics professor who serves as U.S. spokesman for SNO. By accounting for the missing neutrinos, the findings—widely reported in the media, including The New York Times, The Washington Post and The Philadelphia Inquirer—prove that the solar model is correct, and open the door for further research.