The Four Solar Neutrino Problems
This color viewgraph compares the predictions of the standard solar model
with the total observed rates in the six solar neutrino experiments:
chlorine, SuperKamiokande,
Kamiokande, GALLEX, SAGE, and SNO. The model predictions are
color coded with different colors for the different predicted neutrino
components. For both the experimental values and the predictions, the
1 sigma uncertainties are indicated by cross hatching.
I use this viewgraph to explain the ``four solar neutrino
problems'' that suggest that new neutrino physics is required to
explain the results of the solar neutrino experiments. The problems
exist because it is assumed, following the minimal standard model,
that essentially nothing happens to the neutrinos after they are
created in the center of the sun. I believe this is the most important
viewgraph that I show in my general colloquia on solar neutrinos and
therefore I spend much of my time explaining this figure.
In all six cases, the blue experimental values are significantly less
than the model predictions.
The difference (by a factor of three or more)
between the chlorine measurement of Ray Davis
and the standard solar model
prediction was
the ``solar neutrino problem'' for two decades. The
discrepancy between measured and predicted
absolute rates was strengthened at the beginning of the
1990's by the measurement by the Kamiokande experiment
of the 8B neutrino flux. For Kamiokande, which has a
threshold of 7.5 MeV (compared to 0.8 MeV for the chlorine
experiment), the discrepancy is approximately a factor of two.
The discrepancy in absolute rates is the first ``solar neutrino problem.''
Hans Bethe and I pointed out (in 1990) a second solar neutrino
problem, namely, the rate of just the 8B neutrinos observed
in Kamiokande exceeds the total measured rate in the chlorine
experiment if
the energy spectrum of the solar neutrinos is
not changed by new neutrino physics. This problem is exacerbated by
the fact that significant contributions are also expected in the
chlorine experiment from 7Be neutrinos and from CNO
neutrinos. The predicted rate from the 7Be neutrinos is
well determined, especially since the related 8B neutrinos
are observed to be depleted only by a factor of two.
The GALLEX and SAGE experiments present the third, essentially
independent solar
neutrino problem. The total observed rate is accounted for by the pp
neutrinos, whose flux I believe that I can calculate to an accuracy of
1 percent. Therefore,
the gallium experiments do not leave any room for the reliably
calculated 7Be neutrinos. This is the reason why the third
solar neutrino problem is sometimes referred to as ``the problem of
thee missing 7Be neutrinos.'' Moreover, both the GALLEX
and
SAGE experiments have been directly
calibrated with a radioactive source, 51Cr, that emits
neutrinos with similar energies to the 7Be neutrinos.
Most recently and perhaps most dramatically, the SNO experiment has
shown that the CC rate (from electron type neutrinos only) in a
deuterium detector is only 0.35 of the standard model prediction. The
Super-Kamiokande experiment, which measures the CC rate plus--with reduced
efficiency--the muon and tau neutrinos, observes 0.46 of the standard
model prediction. The fact that Super-Kamiokande observes 0.46 (with
some sensitivity to all three neutrinos) and SNO observes only 0.35 of
the standard rate (from only electron type neutrinos) proves that some
electron type neutrinos become muon and tau neutrinos after they are
created in the center of the sun.
Color Viewgraph (postscript)
Color Viewgraph (jpg file)
Back to John Bahcall's Neutrino Viewgraphs
Address questions and comments about this server to webmaster@sns.ias.edu
