The 1 July issue of Physical Review Letters reports an important result from the Sudbury Neutrino Observatory (SNO), 2 km underground in an Ontario nickel mine. 1 This much-anticipated paper describes the first direct measurement of the total flux of neutrinos (above the detector’s energy threshold) arriving from the core of the Sun, irrespective of any “flavor” metamorphoses along the way. And that total flux turns out to be in excellent agreement with the neutrino output predicted by the so-called standard solar model (SSM).
That reassuring accord does much more than simply bolster our confidence that astrophysicists understand how the Sun works. It also confirms the particle physicists’ presumption that neutrinos are capable of more tricks than the minimal standard particle theory permits: They can change flavor as they travel. That presumption has grown gradually with three decades of observed shortfalls of solar neutrinos. The nuclear processes that power the...
