Until today, the solar neutrino detected by the experiment are much less than prediction in theory and this is called as solar neutrino problem. The PP chain is most important energy source in stars with mass below 1.5 times the mass of the Sun. In the Sun 91% of the energy is produced by the PPI chain.
In the pp chain of PPI branch, four protons are transformed into one Helium nucleus, two positrons, two neutrinos and radiations. The input and output constituents of the PPI, PPII and ppIII are as follows:
|I||,||fusion, proton decay, electron capture|
|II||fusion, electron capture, fission|
|III||fusion, proton decay, fission|
It can be seen that in all three pp chains, neutrinos are produced due to the thermonuclear fusion [PPI: ], electron capture [PPI: ], [ PPII: ] and decay [ppIII: ]
Neutrino interacts very weakly with matter and escape out of the star (or from the sun). It is estimated the amount of neutrino intercepted by the earth each day. Several precise experiments are conducted to detect the amount of neutrino (solar) emitted from the sun since 1975. Until today, the solar neutrino detected by the experiment are much mess than predicted in theory. This contradiction suggests that either our understanding of Sun is incomplete or the energy production mechanism via pp chain is wrong. This is called solar neutrino problem.
One possibility is that there could be three types of neutrinos (Dirac, scalar, Majona) as suggested by recent theories, and as neutrinos leave the core of the sun, they may possibly change into a type that is undetectable using today’s instruments. The definite proof is yet to come.
Recently SNO at Canada detected and measured neutrinos other than electron neutrino, claiming to solve the solar neutrino problem. Solar neutrino have a ‘multiple personality disorder’. They are created as electron neutrinos in the pp reactions in the sun, but on the way to the Earth they change their type. For neutrino, the origin of the personality disorder is a quantum mechanical process called “neutrino oscillation”. The number of personality changes, or oscillations, depends upon the neutrino energy. At higher neutrino energies, the process of oscillation is enhanced by interactions with electrons in the Sun or in the Earth.