Number 79, May 8, 1992 by Phillip F. Schewe and Ben Stein
THE ELECTRON ANTINEUTRINO MASS can be no larger than 8 eV. This new upper limit was established by Wolfgang Stoeffl at Livermore who studied the beta decay of tritium, an experiment in which the neutrino's mass (or at least an upper limit) is inferred from a careful energy accounting for a process in which a neutron inside a tritium nucleus decays into a proton, an electron, and an antineutrino. One unsettling aspect of the mass calculation is the fact that the square of the neutrino mass would seem to have a negative value, which is nonsense. Stoeffl, reporting his results at the recent APS meeting in Washington, D.C., said that other experimenters have encountered the same effect. Such calculational oddities sometimes lead scientists to suspect that "new physics" is at work. (Science News, 2 May 1992.)
EUROPEAN PHYSICS has had a mixed success in the past decade. In condensed matter physics, Nobel prizes were won for the discovery of the quantum Hall effect, scanning tunneling microscopy, and high-temperature superconductivity, but there has been little important follow-up research in these areas. On the other hand, Grenoble, France will soon possess both the world's most powerful neutron source (Institute Laue-Langevin) and the European Synchrotron Radiation Facility (ESRF), a source of hard x rays. In optical astronomy, the European Southern Observatory (ESO), at viewing sites in Chile, currently operates the 3.5-m New Technology Telescope (NTT) and in 1999 will unveil the Very Large Telescope (VLT), which will consist of four 8-m telescopes. In particle physics, CERN had most of the glory in the 1980's, what with the discovery of the W and Z bosons and later, toward the end of the decade, with the detailed measurement of the Z's mass at LEP. The HERA electron-proton collider in Hamburg, about to start experiments, and the proposed LHC proton-proton collider at CERN should make the 1990's interesting as well. (Science, 24 Apr. 1992.)
SECOND-GENERATION DETECTORS FOR DARK MATTER are in development. The search for the missing mass will intensify now that the COBE measurements suggest that between 20 percent and 90 percent of the matter in the universe consists of particles or objects that scientists have not yet detected. However, theorists believe that one leading candidate for dark matter, known as a WIMP (for weakly-interacting massive particle), would collide occasionally with ordinary matter. One approach to looking for WIMPs has been to build sensitive detectors, which traditionally measure one of the by-products of nuclear collisions, such as an ionization of electric charge, a flash of light, or the release of a phonon. A problem with these detectors is that it is often very difficult to distinguish signals caused by bona-fide nuclear collisions from those arising from the radioactive decays of detector impurities. However, second generation detectors, being developed independently by a U.S. team at Berkeley and a European team at the University of Rome, will measure two of the by-products. The ratio of energies between the by-products are quite distinct for radioactive decays and nuclear collisions, thereby making it easier to pinpoint a collision of a possible dark-matter particle. (New Scientist, 24 April 1992.)
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