But soon, the excited expression on Qiao Anhua's face retracted.

"Professor Pang, it is undeniable that your theory is wonderful, but the problem is that we must find the inert neutrino you mentioned in order to confirm the correctness of your theory, according to the results of the calculations in your paper, this neutrino exists for a short time, and it is difficult to react with other substances, just how to design experiments to find it, is a big problem!"

Pang Xuelin smiled faintly: "Professor Qiao, do you remember the mystery of the disappearance of solar neutrinos?" ”

"The mystery of the disappearance of solar neutrinos?"

Qiao Anhua was slightly stunned, and his brows furrowed slightly.

He certainly knew about this well-known puzzle in the history of science.

In the first half of the twentieth century, physicists generally believed that the sun emits light due to the constant nuclear fusion reactions from hydrogen to helium that occur within it.

According to this theory, every 4 protons (i.e., protons) inside the Sun are converted into 1 helium nucleus, 2 positrons, and 2 mysterious neutrinos.

It is the energy released by this nuclear fusion reaction that the sun shines and feeds everything on earth.

As thermonuclear reactions progress, neutrinos are continuously released.

Since the mass of 4 protons is greater than the mass of 1 helium nucleus plus the mass of 2 positrons and 2 neutrinos, the reaction releases a large amount of energy.

A small fraction of this energy eventually reaches the Earth in the form of sunlight.

This nuclear reaction is the most frequent reaction that occurs inside the Sun.

Neutrinos can easily escape from the interior of the Sun, and their energy does not come in the form of light and heat.

Sometimes the neutrino energy produced by thermonuclear reactions is relatively low, and the energy taken away is less, so the sun gains more energy.

If the energy of the neutrinos is relatively high, the sun will get a little less energy.

Neutrinos are uncharged and have no internal structure.

In the Standard Model of elementary particle physics, neutrinos have no mass.

There are about 100 billion solar neutrinos per square centimeter that reach the Earth's surface every second, but we don't feel them because the probability of neutrinos interacting with matter is very small. For every 100 billion solar neutrinos that pass through the Earth, only 1 interacts with the material that makes up the Earth. Since neutrinos interact with other particles with a negligible chance, they can easily escape from the interior of the Sun and give us important information directly about the nuclear reactions inside the Sun.

There are 3 different types of neutrinos in nature, and the neutrinos produced by nuclear reactions inside the sun are electron-type neutrinos, and the production of such neutrinos is associated with electrons. The other two types of neutrinos are μ neutrinos and τ neutrinos, which can be produced in accelerators or exploding stars, and are associated with charged μ and τ subons, respectively.

In 1964, Raymond Davis and John Bacow proposed an experimental scheme to test whether nuclear reactions that provide solar energy were fusion reactions.

John Backau and his colleagues used a sophisticated computer model to calculate the number of solar neutrinos of different energies.

Because solar neutrinos react with chlorine to release radioactive argon atoms, they also counted the number of observations in a giant vat filled with perchloroethylene.

Although the idea seemed impractical at the time, Davis believed that using a container the size of a swimming pool filled with pure perchloroethylene as a detector would measure the amount of argon produced each month predicted by theory.

The results of Davis's earliest experiments were published in 1968.

The number of cases he detected was only one-third of the theoretical prediction. The inconsistency between the number of cases predicted by this theory and the experiment came to be known as the "solar neutrino puzzle", more popularly known as the "mystery of the disappearance of neutrinos".

In order to explain the solar neutrino problem, three possible solutions have been proposed.

The first option suggests that there may be something wrong with the theoretical calculations, and that there may be errors in two places: either there is a problem with the solar model that causes the theoretical prediction of the number of solar neutrinos to be incorrect, or there is a problem with the calculated rate of generation.

The second explanation is that perhaps Davis's experiment was wrong.

The third option, the boldest and the most discussed, argues that the solar neutrino itself changes as it travels from the Sun to the Earth through cosmic space.

Over the next 20 years, many people re-carefully calculated the number of solar neutrinos produced. The accuracy of the data used in the calculations is constantly improving, and the results are becoming more accurate.

In the end, it was found that there were no obvious errors in the calculation of the number of neutrinos derived from the solar model and the number of neutrino cases that could be detected by Davis's experimental device.

At the same time, Davis improved the accuracy of his experiments and conducted a series of different tests to confirm that he did not ignore certain neutrinos.

No errors were found in his experimental setup. The problem of inconsistencies between experiments and theories remains unresolved.

The third explanation mentioned earlier was proposed in 1969 by former Soviet scientists Bruno Pontekwe and Vladimir Glipov.

The idea is that the properties of neutrinos are not as simple as physicists originally thought, that neutrinos may have a resting mass and that different types of neutrinos can be converted into each other, the latter being known as neutrino oscillations.

When this idea was first proposed, it was not accepted by most physicists. But as time went on, more and more evidence began to favor the existence of neutrino oscillations. This is a new kind of physics that goes beyond the framework of the standard model.

In 1989, 20 years after the results of the first solar neutrino experiment were released, a Japan-US experimental group (Kamiokande Cooperation Group) led by Masatoshi Koshiba and Yoji Totsuka reported the results of their experiments. They filled a huge detector with pure water to detect the scattering rate between electrons in the water and high-energy neutrinos from the sun.

The experimental device is highly accurate, but it can only detect high-energy solar neutrinos. This high-energy neutrino comes from a relatively rare process in the thermonuclear reaction inside the Sun, the decay of the elements. Davis's original experimental setup used chlorine, but it was also able to detect neutrinos in this energy region.

The Kamiokan experiment confirmed that the number of neutrinos observed was indeed less than the theoretical prediction of the solar model, but it revealed that the theory and experiment were less inconsistent than Davis's experiment.

Over the next 10 years, three new solar neutrino experiments compounded the problem of missing neutrinos.

By the German Tyre?? The GALLEX laboratory led by Kestein and the SAGE laboratory led by Vladimir Glipov each used detectors filled with gallium to detect low-energy solar neutrinos and found that the low-energy neutrinos were also lost.

In addition, the Super Kamiokande Experiment, led by Yoji Totsuka and Yoichiro Suzuki, used a huge detection device containing a total of 50,000 tons of water to measure high-energy solar neutrinos more accurately, convincingly confirming the neutrino loss observed by Davis's experiment and the Kamiokande experiment.

In this way, both high-energy and low-energy solar neutrinos are missing, but in different proportions.

At 12:15 p.m. on June 18, 2001, the Neutrino Experiment team, led by Canadian Arthur MacDonald, made an exciting announcement: they had solved the solar neutrino puzzle.

The international cooperation team used 1,000 tons of heavy water to detect neutrinos.

The probe was placed in a mine 2,000 meters below the southern Canadian city of Sudbury. They used a new method to detect solar neutrinos in the high-energy region that was different from the Kamiokande experiment and the Super Kamiokande experiment. This experiment is called the SNO experiment.

In SNO's initial experiments, the heavy water detection device they used was in a state that was only sensitive to electron neutrinos.

The number of electron neutrinos observed by scientists at SNO is about one-third of the predicted value of the standard solar model, and the previous Super Kamiokande experiment is sensitive not only to electron neutrinos, but also to other types of neutrinos, so the number of neutrinos observed is about half of the theoretical expectation.

If the Standard Model is correct, the experimental results of the SNO should be consistent with that of Super Kamiokande, that is, neutrinos from the sun should all be electron neutrinos. The inconsistencies in the results of the two experiments suggest that the Standard Model for describing the properties of neutrinos is problematic, or at least incomplete.

Combining the experiments of SNO and Super Kamiokande, the SNO collaboration determined not only the number of electron neutrinos, but also the total amount of three types of neutrinos from the sun, which was consistent with the predictions of the solar model.

Electron neutrinos make up one-third of all neutrinos.

In this way, the problem is clear: although the number of electron neutrinos observed on the ground accounts for only one-third of the total number of neutrinos in the Sun, the latter has not decreased; The lost electron neutrinos did not "disappear", but were transformed into μ neutrinos and τ neutrinos, which are difficult to detect.

This groundbreaking result was published in June 2001 and was soon supported by a series of other experiments.

The SNO collaboration measured the number of all three high-energy neutrinos on their heavy water detection device, which was unique at the time. Their experimental results show that most neutrinos are produced inside the sun, and they are all electron neutrinos when they are generated.

When they reach Earth, some of the electron neutrinos are transformed into μ neutrinos and τ neutrinos.

The key to the SNO experiment is the measurement of the total number of neutrinos in the three species. It is thanks to the determination of the total number of 3 neutrinos that physicists are able to convincingly explain the mystery of the disappearance of solar neutrinos without relying on specific theoretical models.

……

"Professor Pang, you mean that the existence of such inert neutrinos can be found through solar neutrino experiments?"

Qiao Anhua looked at Pang Xuelin and frowned.

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