“Neutrinos are so beautiful, so incredible. We need to understand them better,” says Guido Drexlin, project leader of the Karlsruhe Tritium Neutrino Experiment (KATRIN) in Germany. Billions of neutrinos fly by—and through—us constantly. But because those fundamental particles are neutral and weakly interacting, they remain elusive: What is their mass? What is the mass hierarchy of the three neutrino types? Are neutrinos their own antiparticles? Can they help explain the dominance of matter over antimatter in the universe? What is their role in the creation of the elements?

The gigantic KATRIN experiment at the Karlsruhe Institute of Technology (KIT) leads a new generation of varied approaches aimed at nailing down the tiny neutrino mass. Scientists are testing the apparatus now and will begin collecting data early next year.

With the 1998 discovery at Super-Kamiokande in Japan that neutrinos oscillate among flavors (see Physics Today, August 1998, page 17)...

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