The Science Fiction World of Xueba

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

"Professor Pang, it’s undeniable that your theory is wonderful, but the problem is that we have to find the inert neutrinos you said in order to confirm that your theory is correct. According to the results calculated in your paper, this This kind of neutrino exists for a short time, and it is difficult to react with other substances. How to design an experiment to find it is a huge problem!"

Pang Xuelin smiled faintly: "Professor Qiao, do you remember the mystery of the disappearance of the sun's neutrinos?"

"The mystery of the disappearance of the sun's neutrino?"

Qiao Anhua froze slightly, frowning slightly.

He certainly knows this famous problem in the history of science.

In the first half of the twentieth century, physicists generally believed that the sun glows due to the continuous nuclear fusion reaction from hydrogen to helium.

According to this theory, every 4 hydrogen nuclei (ie protons) in the sun are converted into 1 helium nuclei, 2 positrons, and 2 mysterious neutrinos.

It is precisely the energy released by this nuclear fusion reaction that glows and heats up, feeding everything on earth.

As the thermonuclear reaction progresses, neutrinos are continuously released.

Since the mass of 4 protons is greater than that of 1 helium nucleus plus 2 positrons and 2 neutrinos, the reaction must release a lot of energy.

A small part of this energy eventually reaches the earth in the form of sunlight.

This nuclear reaction is the most frequent reaction inside the sun.

Neutrinos can easily escape from inside the sun, and their energy does not appear in the form of light and heat.

Sometimes the energy of neutrinos produced by thermonuclear reaction is lower and the energy taken away is less, then the sun gains more energy.

If the energy of the neutrino is relatively high, the energy obtained by the sun will be relatively less.

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 reaching the surface of the earth every second, but we cannot feel them because the probability of neutrinos interacting with matter is very small. For every 100 billion solar neutrinos passing through the earth, only one interacts with the material that makes up the earth. Because the probability of neutrino interacting with other particles is very small, it can easily escape from the inside of the sun and directly bring us important information about the nuclear reaction inside the sun.

There are three different types of neutrinos in nature. The neutrinos produced by nuclear reactions in the sun are electron-type neutrinos. The production of such neutrinos is associated with electrons. The other two types of neutrinos are muon neutrinos and tau neutrinos, which can be generated in accelerators or exploding stars, and are associated with charged muons and τ neutrons, respectively.

In 1964, Raymond Davis and John Bekao proposed an experimental scheme to test whether a nuclear reaction that provides solar energy is a fusion reaction.

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

Since solar neutrinos would react with elemental chlorine to release radioactive argon atoms, they also counted the number observed in a giant barrel filled with tetrachloroethylene.

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

The earliest experimental results of Davis were published in 1968.

The number of cases he detected was only one-third of the theoretically predicted value. The problem that the number of cases predicted by this theory is inconsistent with the experiment was later called the "Solar Neutrino Problem", and the more popular saying "The Mystery of the Missing Neutrino".

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

The first scheme believes that there may be a problem with theoretical calculations, which may be wrong in two places: or there is a problem with the solar model, resulting in the wrong number of solar neutrinos predicted by the theory, or a problem with the calculated production rate.

The second explanation is that Davis's experiment may be wrong.

The third scheme is the most daring and the most discussed one. It believes that the solar neutrino itself has changed in the process of passing through the universe from the sun to the earth.

In the next 20 years, many people have carefully recalculated the number of solar neutrinos. The accuracy of the data used in the calculation is constantly improving, and the results obtained are more accurate.

Finally, it was found that the number of neutrinos derived from the solar model and the calculation of the number of neutrino cases detectable by Davis' experimental device were not obvious errors.

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

No errors were found on his experimental device. The problem of inconsistency between experiment and theory is still unresolved.

The third explanation mentioned earlier was proposed by the former Soviet scientists Bruno Pontecway and Vladimir Glibov in 1969.

This idea believes that the nature of neutrinos is not as simple as physicists had originally imagined. Neutrinos may have a rest mass and different types of neutrinos can be transformed into each other, the latter being called neutrino oscillation.

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

In 1989, 20 years after the results of the first solar neutrino experiment were released, a Japanese-American experimental group (Shinoka Cooperation Group) led by Koizumi Changjun and Totsuka Yoji reported their experimental results. 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.

This experimental device has high accuracy, but can only detect high-energy solar neutrinos. This high-energy neutrino comes from a relatively rare process in thermonuclear reactions inside the sun, namely the decay of elements. Davis's initial experimental device used chlorine, but it could also detect neutrinos in this energy zone.

The Kamioka experiment confirmed that the number of neutrinos observed is indeed less than the theoretical prediction of the solar model, but the degree of inconsistency between the theory and the experiment revealed is smaller than that of Davis' experiment.

Over the next 10 years, three new solar neutrino experiments have complicated the problem of neutrino disappearance.

The GALLEX laboratory led by German Tierkestein and the SAGE laboratory led by Vladimir Glibov respectively used detectors filled with gallium to detect low-energy solar neutrinos and found low-energy neutrinos. There is also the problem of loss.

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

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

At 12:15 on June 18, 2001, the neutrino experiment group composed of American, British and Canadian scientists led by Canadian Arthur McDonald announced an exciting news: they solved the solar neutrino Child puzzle.

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

The detector was placed in a mine 2,000 meters underground in the city of Sudbury in southern Canada. They used a new method different from the Kamioka experiment and the Super Kamioka experiment to detect solar neutrinos in high-energy regions. This experiment is called the SNO experiment.

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

The number of electron neutrinos observed by scientists in SNO is about one-third of the predicted value of the standard solar model, and the previous super kamioka experiment is not only sensitive to electron neutrinos, but also certain types of neutrinos. Sensitivity, so the number of neutrinos observed is more than half of the theoretical expected value.

If the standard model is correct, the experimental results of SNO should be consistent with that of Super Kamoka, that is, all neutrinos from the sun should be electron neutrinos. The results of the two experiments are inconsistent, indicating that the standard model for describing the properties of neutrinos is problematic, at least incomplete.

Combining the experiments of SNO and Super Kamioka, the SNO cooperation group not only determined the number of electron neutrinos, but also determined the total amount of three types of neutrinos from the sun. The results are consistent with the predictions of the solar model.

Electron neutrinos account for 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 solar neutrinos, the latter has not decreased; the lost electron neutrinos have not "disappeared" ", just transformed into difficult to detect muon neutrinos and tau neutrinos.

This epoch-making result was published in June 2001~www.readwn.com~ and was soon supported by a series of other experiments.

The SNO team 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.

Upon reaching the earth, some electron neutrinos are transformed into muon neutrinos and tau neutrinos.

The key to the SNO experiment is the measurement of the total number of three neutrinos. It is precisely because of the determination of the total amount of three kinds of neutrinos that physicists can convincingly explain the mystery of the disappearance of solar neutrinos without relying on specific theoretical models.

...

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

Qiao Anhua looked at Pang Xuelin and frowned.

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