The mystery of the missing neutrinos

Detection of solar neutrinos in a one mile deep
South Dakota mine (1972)

One of the pseudoscientific hoaxes running in Internet says something like this:

According to the justification of the Nobel Committee in 2015, Takaaki Kajita and Arthur B. McDonald received their Nobel Prizes for the discovery of neutrino oscillations, which shows that neutrinos have mass. The Nobel Committee donated again Nobel Prizes and 8 million Swedish Coronas for NOTHING, since the numerical value of the frequency, impulse, kinetic energy, and therefore the mass of the neutrinos, are still unknown. Without the numerical value of the frequency, it has not been proved that the neutrinos oscillate and have mass. According to the pseudo-scientific theory of modern physics, one light-year thick layer of lead absorbs only half of the neutrinos, then how is it possible to detect neutrinos and the neutrino oscillation? Since Takaaki Kajita and Arthur B. McDonald have not one light-year thick layer of lead in their laboratories, therefore the discovery of the neutrino oscillations is only a scam! The neutrino is an invented particle, which comes from the wrong pseudo-scientific theory of modern physics.

This paragraph, which calls pseudoscience the standard theory of particle physics, contains a few glaring mistakes that I will try to detail here:

Wolfgang Ernst Pauli

• The existence of the neutrino was predicted in 1930 by Wolfgang Pauli, to avoid the infringement of the principle of conservation of energy in the beta decay, where one neutron of an atomic nucleus is transformed into a proton and an electron is expelled. According to Pauli, the missing energy is taken by an unknown particle with very small mass which had to be neutral, to comply with the principle of conservation of electric charge. Enrico Fermi proposed the name neutrino (Italian diminutive for neutral).
• The neutrino was experimentally detected in 1956 by Frederick Reines and his team, by capturing antineutrinos generated in a nuclear reactor. When an antineutrino collides with a proton, they transform into a neutron and a positron. Reines received the Nobel Prize in physics in 1995, 39 years later. When the quoted text says that the neutrino is an invented particle, it just exhibits ignorance.
• In 1962, Lederman, Schwartz and Steinberger showed that, besides the neutrino associated with the electron, there is another associated with the muon, and detected its interactions with ordinary atoms. In 1988 they were granted the Nobel Prize.
• When in 1975 the tau particle was discovered (the third lepton in the electron family), it was naturally assumed that it would also have an associated neutrino. Its interactions were experimentally discovered in 2000 at Fermilab.
• The standard theory of particle physics predicts that neutrinos should have no mass (their mass should be zero), in which case they would travel at the speed of light.
• The neutrino is a subtle particle that barely interacts with the atoms of ordinary matter. Suppose it is true that one light-year thick layer of lead absorbs only half of the neutrinos that traverse it. Then a one meter thick layer of lead would absorb 5,3x10^-17xN neutrinos, where N is the number of neutrinos that reach the lead. If we have on the surface of the Earth a cube of lead with a volume of one cubic meter, every second it would receive from the sun N=66x10¹³ neutrinos, and it would absorb 0,035 neutrinos per second, or about one neutrino every half minute. This experiment does not seem so difficult to perform as the quoted paragraph implies.
• In practice neutrinos are not detected with blocks of lead, but with very large amounts of water stored in underground caverns, to avoid contamination with other particles that cannot go through the Earth. Experiments conducted since the late 60s detected, among the neutrinos coming from the sun, around one third of the number expected, given the amount of energy emitted by the sun, which is easy to calculate. The problem was called the case of the missing neutrinos.
• Since there are three kinds of neutrinos, those associated with the electron, muon and tau particle, if they could transform into each other on their way from the sun to Earth, we would have a very elegant solution to the above problem: the sun produces only electron (anti-)neutrinos, which are those detected. If two-thirds of these neutrinos have been converted into muon and tau neutrinos on their way, we will detect just one third of those expected.
• The trouble is that, according to the standard theory of particle physics, neutrinos should have zero mass, but to be transformed into each other they must have some mass, albeit very small. There is here a discrepancy that has not yet been resolved.
• In recent decades, there has been abundant experimental confirmation of the hypothesis that neutrinos oscillate (transform into each other). In 2015 the Nobel Prize in physics was awarded to Takaaki Kajita and Arthur B. McDonald for their pioneering work in this field.
• It is true that the mass of the neutrino is not known, but an upper limit has been set at 5,5 eV/c², around 200 million times smaller than the proton.

In summary: it is evident that the paragraph quoted above is just a mixture of confused and meaningless assertions. Scientific theories are not as complete as sometimes we are led to believe, but they are not fraud, as this canard clearly states.

The same post in Spanish
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Manuel Alfonseca