Solar‐neutrino hunters still seek explanation

More than ten years of painstaking measurements of the solar‐neutrino flux have been summarized, and at least as many years of future experimentation have been previewed, in conference talks and in journal articles over the last year. At the Conference on the Status and Future of Solar‐Neutrino Research held at Brookhaven National Laboratory in January, Raymond Davis Jr and his coworkers from Brookhaven presented a statistical average of the past eight years of measurements of the solar‐neutrino flux. The value was $\text{1.7\hspace{0.17em}±\hspace{0.17em}0.4}$ SNU (one solar‐neutrino $\mathrm{unit}{\text{\hspace{0.17em}=\hspace{0.17em}10}}^{\text{−36}}$ captures per target atom per second), about one‐third that predicted by the standard solar model (4.7 SNU). Unlike the first data that hinted at the unexpectedly low value, the current results have gained general acceptance because the careful refinements and checks in the intervening years have dispelled most doubts. No one knows whether the current discrepancy between theory and experiments reflects an inadequate understanding of the dynamics of the Sun’s core or a lack of knowledge of some aspect of nuclear or neutrino physics (although there tends to be some mutual finger pointing!). To resolve the question, many research groups have advanced concepts for future experiments. Feasibility studies of these proposed experiments continue to be updated and debated.