Do ghostly, imperceptible particles called "sterile neutrinos"
wander the universe? The question has given physicists sleepless
nights since evidence for the particles emerged a decade ago.
But now a new experiment has poured cold water on the idea,
reassuring many scientists that their ideas are on the right
track. "Our results are the culmination of many years of very
careful and thorough analysis - scientists everywhere have been
eagerly waiting for our results," says Janet Conrad, a
spokeswoman for the experiment at Fermilab, near Chicago in
Illinois, US. She announced the result at a Fermilab meeting on
Wednesday. Neutrinos are lightweight particles that whiz around
the universe, barely interacting with matter. They stream out
from nuclear reactions in the Sun and continually flood straight
through the Earth. The particles come in three different types,
or "flavours", dubbed electron, muon and tau. And several
experiments have proved that neutrinos and their antiparticle
counterparts can flip from one fl