DETECTION OF EARTH’S MAGNETIC FIELD USING NEUTRINOS has been accomplished at the Super-Kamiokande detector located underneath Mt. Ikenoyama in Japan. Here is the sequence of events: a cosmic ray proton strikes an oxygen or nitrogen atom in Earth’s upper atmosphere, creating a neutrino which passes freely into the Earth where it may find its way into Super-Kamiokande, a device consisting chiefly of 50,000 tons of pure water. In the water the neutrino (when it bothers to interact at all) will typically convert into a muon or electron, plus light, which is recorded in surrounding photodetectors. In this process, the neutrino and its daughter muon or electron track pretty closely the trajectory of the original cosmic ray proton. But the incoming cosmic ray flux, which would otherwise be isotropic, is shaped by the Earth’s magnetic field. This acts as a sort of prevailing wind which sets up an east-west anisotropy in cosmic rays. This anisotropy, measured as long ago as the 1930s, should be matched by a corresponding anisotropy in neutrinos, which is precisely what the Super-Kamiokande team now finds. This measurement, while it says nothing new about Earth’s magnetic field, does reassure the researchers that their detection of neutrino oscillation (one of the top physics stories of 1998, see Update 375) stands on a firm understanding of the complex chain of events whereby a cosmic ray in outer space leads to a burst of light in a cavern beneath Japan. (Futagami et al, Physical Review Letters, 28 June 1999; team leader, Y. Totsuka, Tokyo University, totsuka@suketto.icrr.u-tokyo.ac.jp
; some US contacts: Henry Sobel, UC Irvine, 949-824-6911, sobel@uci.edu; Lawrence Sulak, Boston University, 617 353-9454, sulak@bu.edu; paper available to science writers from AIP public information; 
