Neutrino Mass: A Positive View
Thomsen, Dietrick E., Science News
Neutrino mass: A positive view
Consideration of the evidence fromsupernova 1987A now leads a number of physicists to conclude that neutrinos probably do have a rest mass, in contrast to previous work that interprets the evidence negatively. One group--Hong-Yee Chiu, Yoji Kondo and Kwing L. Chan of the NASA Goddard Space Flight Center in Greenbelt, Md.--finds a value of about 3.6 electron volts (eV) for a possible neutrino mass. Ramanath Cowsik of Washington University in St. Louis and a group at the Max Planck Institute in West Germany both say they find two values, 4 eV and 20 eV.
Neutrinos were originally thought tohave zero rest mass. Recent theories of particle physics and cosmology would like them to have a small rest mass nevertheless. If neutrinos have a rest mass, those that leave the supernova with higher energy come to earth sooner than those with lower energy. If two neutrinos with different energies leave the supernova at the same time, the rest mass can be calculated from the difference in their arrival times.
Finding the proper neutrino pairs inthe data is the trick: Nobody knows when a given neutrino left the supernova. Chiu's group paired each neutrino with every other and calculated trial masses. In this procedure the true pairs should show up by giving the same number every time; the false ones give a scatter of numbers. …