MTL - The Science Fiction World of Xueba-Chapter 513 Type 4 neutrino

"Professor Pang, you mean that in theory, there may be a fourth kind of neutrino, and this neutrino cannot be observed through the decay of the Z boson?"

In the laboratory of the Institute of High Energy Physics of the Chinese Academy of Sciences, Qiao Anhua, director of the Institute of High Energy Physics, looked at Pang Xuelin and frowned.

In the past six months, Pang Xuelin has not been idle.

While proposing the Earth Cannon Project, he also contributed many top papers in the fields of mathematics and physics.

Some are his previous scientific research results, and some are simply derived from systematic rewards.

Therefore, in the scientific community, Pang Xuelin's name is quite popular.

This is why he suggested that there may be a fourth type of heavy neutrino, and Qiao Anhua did not directly refute.

Pang Xuelin nodded and smiled: "According to the model calculation results I gave, there should indeed be such a heavy neutrino."

"But... why haven't we found such neutrinos until now?"

Qiao Anhua asked the key to the question.

The first time humans detected neutrinos was an experiment conducted by the American physicist Lenis and Cohen team in 1956 using the reactor at the Savannah River plant.

The experimental reactor produced a powerful neutron flow accompanied by a large amount of beta decay, which emitted electrons and antineutrinos. The antineutrinos bombarded protons in the water to produce neutrons and positrons. The neutrons and positrons entered the detector. In the target liquid, neutrons are absorbed, the positrons and negative electrons are annihilated, and high-energy γ rays are generated to determine the reaction.

Although the antineutrino flux was as high as 5×10 thirteenth power per square centimeter per second, the number of detections at that time was less than 3 per hour.

In 1983, physicists established the Super Kamioka Detector in Gifu Prefecture, Japan, using the principle of "Celenkov radiation".

The main part of the Super Kamoka detector is a huge water tank built at a depth of 1,000 meters underground, containing about 50,000 tons of high-purity water, and the inner wall of the tank is attached with 11,000 photomultiplier tubes to detect neutrinos Cherenkov light emitted when passing through the water, thereby capturing the trace of neutrinos.

The so-called Cherenkov radiation means that when a charged particle travels through a medium and its speed exceeds the speed υ of light in the medium, Cherenkov radiation occurs, and Cherenkov light is emitted.

Specifically, when a neutrino beam passes through water, it undergoes a nuclear reaction with the water nucleus, generating high-energy negative muons. Since the negative muon advances in the water at a speed of 0.99 times the speed of light, which exceeds the speed of light in the water (0.75 times the speed of light), it will traverse a path of six or seven meters in water and the "Celenkov effect" will occur, radiating the so-called Cherenkov light".

This light not only includes all the continuously distributed visible light in the range of 0.38-0.76 microns, but also has a definite directivity.

Therefore, as long as the high-sensitivity photomultiplier array is used to collect all the "Cherenkov light", the neutrino beam is also detected.

In a sense, this is also the basic principle of neutrino communication technology.

Now, it is already 2075, and different types of neutrino detection technology have already matured, but apart from the three neutrinos mentioned before, humans have not discovered the existence of the fourth neutrino.

The theoretical part and the experiment are either theoretically problematic or experimentally problematic!

From Qiao Anhua's point of view, there are problems with Pang Xuelin's theory.

Pang Xuelin smiled slightly and said, "Professor Qiao, how do we determine the different classifications of neutrinos now?"

Qiao Anhua thought for a while and said: "From an experimental point of view, neutrinos are classified according to the always (the probability effect of quantum mechanics) lepton that accompanies them in weak reactions."

"For example, in the Cowan-Reines experiment where neutrinos were discovered, scientists first assumed that the decay reaction in the nuclear reactor would produce neutrinos. After these neutrinos flew out of the reactor, appropriate detection devices were placed outside the reactor. Detection. The liquid (cadmium chloride) contained in the device contains a large number of protons. Theoretically expects the neutrinos and protons to have an inverse β decay reaction. The positrons can annihilate with the electrons in the detection liquid to generate light, and then pass the photoelectric effect sensor Read this light signal (and the time, energy, etc.). The neutron can be absorbed by the heavy metal (cadmium) in the liquid and emit light. This process is a little slower. The Cowan-Reines experiment saw the two before and after. An optical signal, and the optical signal is as expected, then there is an inverse β decay reaction, which proves the existence of neutrinos."

"Further analysis of this experiment, the light signal generated by the annihilation of positrons and electrons shows that the neutrinos produced by nuclear reactors are accompanied by positrons, so this is actually an anti-electron neutrino. RayDavis, the early discoverer of solar neutrinos I have tried to use neutrinos that also use nuclear reactors to detect with this reaction. But he did not get the expected results from nuclear reactors. Later this same reaction was used to detect solar neutrinos, and the results can be seen This shows that the neutrinos accompanying the e- and e+ reactions are different. The nuclear reactor produces anti-electron neutrinos, and the solar nuclear reaction produces electron neutrinos. The root cause of this is from the left and right sides of the nuclear reaction except for the requirements In addition to the conservation of charge, the conservation of lepton numbers is also required. The lepton numbers of positron and anti-electron neutrinos are recorded as -e, and the lepton numbers of electron and electron neutrinos are +e."

"Laterman et al. then studied the neutrinos produced in the accelerator. The neutrinos produced in the accelerator mainly came from the decay of the π meson. They were expecting two inverse beta decay reactions. However, they did not observe reaction 1, only reaction 2. This shows that the neutrinos produced by the accelerator are always accompanied by positive muons instead of positrons during the inverse β decay reaction. The properties of mums and electrons are similar, but they have a greater mass. They are classified as lepton. This It shows that the conservation of lepton numbers is further subdivided into conservation of electronic lepton numbers and conservation of muon lepton numbers. Therefore, what they observe is the anti-mute neutrino."

"The third type of neutrino was found on the higher-energy accelerator Tevatron (DONUT experiment). Similar to before, they were accompanied by Taozi in the reaction. Taozi is also a kind of lepton, but its mass is even greater than that of protons. Therefore, it takes more energy to make (by Einstein's mass-energy equation), which is why Taozi and Taozi neutrinos were discovered later. Similarly, Taozi also introduced a lepton number for Taozi. The neutral flow channel can detect all kinds of neutrinos, and the current channel can only detect electron neutrinos. In the elastic scattering reaction with electrons, the reaction probability of electron neutrinos is more High. In this way, by analyzing the detection results of the neutral flow channel, the total amount of all types of neutrinos can be obtained, and analyzing the detection results with current can obtain the amount of electron neutrinos, thereby calculating the conversion probability of electron neutrinos."

Qiao Anhua did not succumb, and told how to tell Pang Xuelin about three different kinds of neutrinos.

Pang Xuelin smiled slightly and said, "Professor Qiao, you should know that neutrinos with different flavors can be converted into each other by neutrino oscillation. Have you ever considered whether new neutrinos will be generated during the conversion process? What about you?"

Qiao Anhua was slightly surprised, looking at Pang Xuelin in a puzzled way: "Professor Pang, do you mean?"

Pang Xuelin said: "My idea is whether there is a kind of inert neutrino, such as the conversion of electric neutrinos into Tao neutrinos, firstly by neutrino oscillation, this inert neutrino is converted, and then by This inert neutrino is converted into Tao neutrino, and when Tao neutrino is converted into Miao neutrino, it is also transformed by this inert neutrino, but the time of this process is too short, so that we do not have Enough way to test!"

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