Missing Neutrinos

The solar neutrino problem was a major discrepancy between measurements of the numbers of neutrinos flowing through the earth and theoretical models of the solar interior, lasting from the mid-1960s to about 2002. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics - specifically, neutrino oscillation. Essentially, as neutrinos have mass, they can change from the type that had been expected to be produced in the sun's interior into two types that would not be caught by the detectors in use at the time.

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The Sun is a natural nuclear fusion reactor, powered by a proton-proton chain reaction which converts four hydrogen nuclei (protons) into helium, neutrinos and energy. The excess energy is released as gamma rays and as kinetic energy of the particles, including the neutrinos — which travel from the Sun's core to Earth without any appreciable absorption by the Sun's outer layers. As neutrino detectors became sensitive enough to measure the flow of neutrinos from the sun, it became clear that the number detected was lower than that predicted by models of the solar interior. In various experiments, the number of detected neutrinos was between one third and one half of the predicted number. This came to be known as the solar neutrino problem.

The crux within the solar neutrino problem, and its resolution, lies in the fact that both the interior of the sun and the behavior of travelling neutrinos is unknown to begin with. One may assume one, and determine the other by experiments here on earth. So if you assume the Standard Solar Model is valid, you can derive the propagation properties of neutrinos, like neutrino oscillations, from solar neutrino experiments. And vice versa: If you presume something about the propagation of solar neutrinos, you may derive some conclusions about the validity of solar models.

You cannot derive both. Also, for all the hypothesis above, it should be noted that they are based on the assumptions that the neutrino absorption coefficient in matter is practically zero. Although this result is a consequence of the standard model, By looking at the list of neutrino detectors, it should be clear that this assumption is not backed by direct experimental evidence for all isotopes, all neutrino flavors and all neutrino energy ranges. Most notably, nothing is known about incident neutrinos exciting nuclear resonances like the giant dipole resonance (and others) in heavier nuclei. (the exception is the C12* 15.11 MeV resonance measured in SNO+).

To circumvent the problem associated with "unknown source and unknown propagation", the Double Chooz experiment, like the former Goesgen reactor experiment, will set up detectors in different distances from the source (the reactor). The experimenters from the KamLand experiment just say the antineutrinos "disappear". But those are antineutrino experiments, not solar neutrino experiments. If the adsorption coefficient for neutrino beams in matter is not negligible, the Solar Neutrino Problem would have to be rediscussed.


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