KIP - Cryogenic particle detection - Solar neutrino problem

Solar Neutrino Problem

Neutrinos which are released in fusion processes in the core of the sun reach the earth almost unimpeded. Their rate reflects therefore directly the energy production in the sun. The physical processes inside the sun can be reconstructed, not only qualitatively but also quantitatively very well, from the observation of the properties of the sun. The theoretical description of many experimental data has led to the so-called standard solar model. However, since of 30 years there are experimental hints that the rate of solar neutrinos reaching the earth is significantly reduced compared to the expectation drawn from the standard solar model. Today, after investigations with several different detectors, there is very little doubt about the deficit of solar neutrinos, which is called the solar neutrino problem. However, the spectral distribution of this deficit is not clear yet. Therefore one would like to perform measurements of the solar neutrino spectrum to see in which energy range neutrinos are missing.

If one assumes that the standard solar model is correct, one has to explain why a fraction of the neutrinos 'disappear' on their way to earth. A possible explanation is given by the so-called neutrino oscillation model, which assumes that neutrinos have a finite mass and that they can oscillate between different flavor states. If this is true the electron neutrinos produced in the sun could be partly transform into other neutrino types and will therefore be missed bei detectors for electron neutrinos on earth.

The detection of solar neutrinos involves similar difficulties as the detection of dark matter, since the expected rate is very low. Therefore one has to go in underground laboratories and must find suited ways for reducing the radioactive background. Here some links to solar neutrino detection projects which involve cryogenic detectors:

HERON, Brown University (USA)

Technische Universität München

Fig. 1: Expected solar neutrino flux on earth according to the standard solar model.