Sunspots and neutrinos

Science News 04/21/90 p.245

According to the so-called standard solar model, nuclear fusion reactions at the sun's center pump out vast quantities of energy. About 2 percent of that energy should appear in the form of neutrinos - fundamental particles that interact only weakly with matter.
But that's not what researchers see. Data collected by an Earth-based detector over a period of 20 years suggest that the neutrino flow from the sun varies from time to time rather than remaining constant. Moreover, the flux seems to follow a pattern that runs counter to the rise and fall in the number of sunspots visible on the sun's surface.
"This time variation of the neutrino flux coincides with the well-known 11-year cycle of solar activity", says physicist Kenneth Lande of the University of Pennsylvania in Philadelphia. The neutrino flux is high when solar activity is low and declines to near-zero values as the number of sunspots rises to a peak.
Lande reported the latest measurements from a neutrino detector deep in the Homestake gold mine near Lead. S.D., at this week's American Physical Society meeting in Washington, D.C. The measurements clearly show a sharp drop in neutrino flux starting last year - just as the present solar cycle approached its maximum.
Such a rise and fall in neutrino flow, detected now for the second time in two decades, hints that the effect is real. Lande says. The chance of such a pattern happening randomly is less than 1 percent according to computer simulations. At its peak, the neutrino flux is reasonably close to the value theorists predict the flux from the sun should have. "You can think of the peak level as being the real neutrino flux and the reduced level as being the attenuated or modulated level," Lande says. "Something does something to the neutrinos."
No one yet has a clear picture of what exotic mechanism may be responsible for altering the fundamental nature of neutrinos coming from the sun's center or for the apparent link between solar activity and neutrino physics. Preliminary results expected later this year from two new neutrino detectors should help clarity the matter (Science News: 10/28/89. p.282).