For the next month, Pang Xuelin locked himself in the expert building of the Institute of High Energy Physics of the Chinese Academy of Sciences, studying the world's fundamental physics and the neutrino theory brought out of the world "Whale Song" world.

This look is not a small gain.

In the world of "Earth Cannon", the most widely used field of neutrino technology is neutrino communication.

In the world of "Whale Song", the most widely used neutrino technology is in the field of detection, where scientists use neutrino detectors to detect drugs in various interlayers.

In principle, both use high-energy proton accelerators to accelerate protons to obtain a high-energy electron beam with hundreds of billions of electron volts. It is then used to bombard the target, creating unstable particles.

These particles change constantly, eventually forming neutrinos and other particles, which are then passed through a thick steel plate to sieve out the charged particles to obtain an uncharged neutrino beam.

Neutrino communication is to let these neutrinos pass through water, and then the water will emit blue light, which will be received by a photomultiplier and the information can be obtained.

Neutrino detection is to determine the composition of different media through the different photoelectric signals emitted by neutrinos through different media.

There is no major difference in the fundamental principle between the two.

However, Pang Xuelin found that the research on particle physics in the world of "Whale Song" has one more kind of neutrino than the world of "Earth Cannon", that is, heavy neutrinos.

As we all know, neutrinos belong to the same species of lepton as electrons, μ and τ tons, and there are several ways in which neutrinos are produced in the universe. One is proto, created in the Big Bang, and is now a very cold cosmic background of neutrinos.

The second is the supernova explosion megabody activity, which is produced by the merger of protons and electrons into neutrons during gravitational collapse, SN1987A neutrinos are of this category.

The third type is neutrinos below a dozen MeV produced by light nuclear reactions on stars such as the Sun.

The fourth is that high-energy cosmic ray particles are emitted into the atmosphere and react with the nuclei of the atoms in them to produce π and K mesons, which then decay to produce neutrinos, which are called "atmospheric neutrinos".

Fifth, the collision of high-energy protons in the cosmic ray and the photons of the cosmic microwave background radiation produces π mesons, this process is called "photo-induced π mesons", and the decay of π mesons produces high-energy neutrinos, which are extremely high in energy.

The sixth is that cosmic rays, high-energy protons hit the nucleus of a star cloud or interstellar medium, and the mesons generated by nuclear reactions decay into neutrinos, especially on some neutron stars, pulsars and other stars.

The seventh is neutrinos produced by spontaneous or induced fission products β decay of matter on Earth, which are very rare.

Although they are produced in different ways, scientists have discovered that neutrinos have three "flavors": electric neutrinos (νe), μ neutrinos (νμ), and τ neutrinos (ντ).

Each flavor neutrino has a corresponding antineutrino that is equally electrically neutral and has a spin quantum number of 1/2.

In the Standard Model, the process of neutrino generation follows the law of conservation of lepton numbers.

Since neutrinos are electrically neutral and are also a type of lepton, they do not participate in strong and electromagnetic interactions, but only in gravitational interactions as well as weak interactions.

However, the weak interaction distance is very short, and the gravitational interaction is very weak at the subatomic scale, so neutrinos are not too hindered when passing through ordinary matter, and it is difficult to detect.

Currently, neutrinos can be produced in a variety of ways, such as radioactive decay and nuclear reactions.

Nuclear reactions are taking place all the time inside the sun, and processes such as supernovae are accompanied by violent nuclear reactions, so neutrinos can be detected in cosmic rays.

Most of the neutrinos detected near Earth originate from the Sun.

In fact, the Sun-facing region of the Earth passes through about 65 billion neutrinos from the Sun every square centimeter per second.

It is now recognized that neutrinos oscillate between different flavors during flight, for example, electric neutrinos produced during β decay may become μ neutrinos or τ neutrinos when detected.

This phenomenon shows that neutrinos have mass, and the mass of neutrinos with different flavors is also different.

According to current cosmological data, the sum of the neutrino masses of the three flavors is less than one millionth of the mass of an electron.

Further studies have found that neutrinos (i.e., mass eigenstates) M1, M2, and M3 with definite masses do not correspond one-to-one with taste eigenstates, such as electric neutrinos, μ neutrinos, and τ neutrinos.

For example, M1 with a definite mass can be seen as a combination of neutrinos with three flavors in a certain ratio, while electron neutrinos with a definite taste are also composed of three neutrinos with different masses.

It is this mixing that causes neutrino oscillations.

The oscillations of the three generations of neutrinos can be described by 6 parameters, including two mass squares, three mixing angles, and one CP destruction phase angle.

The solar neutrino experiment measured m2^2-m1^2=7.5×10-5eV^2 and the mixed angle sin^2β12=0.86, and the atmospheric neutrino experiment measured |m3^2-m2^2|=2.4×10^-3eV^2 and sin^2β23≈1.

In the real world, the Daya Bay reactor neutrino experiment led by Wang Yifang, an academician of the Chinese Academy of Sciences, measured the last mixing angle sin^2β13=0.09.

In the world of "Whale Song", humans have measured the parameters of the phase angle of neutrino CP destruction. At the same time, the question of who is heavier in M1, M2, M3 is also determined.

On this basis, the properties of electric neutrinos, μ neutrinos, and τ neutrinos were thoroughly clarified.

But there is a problem, scientists in the world of "Whale Song" have found that according to the measured results, there should theoretically be a fourth type of neutrino, which they named heavy neutrinos, also known as inert neutrinos.

Under the existing conditions, the best results for the determination of neutrino species come from the observation of the decay of the Z boson.

This particle decay produces various types of light neutrinos and their counterparts as antineutrinos. The more types of light neutrinos produced, the shorter the corresponding lifetime of the Z boson.

However, the presence or absence of inert neutrinos cannot be determined by observing the decay of Z-bosons.

The observations of cosmic microwave background radiation obtained by microwave anisotropy detectors are compatible with the case of three or four neutrinos.

……

Heavy neutrinos!

Pang Xuelin wrote these four big characters on the manuscript paper and then circled them.

Neither in the world of "Whale Song" nor in the world of "Earth Cannon" has been able to observe the existence of heavy neutrinos in experiments.

Pang Xuelin faintly felt that if he wanted to complete the research and development of a new generation of stratino neutrino CT detection instruments, this heavy neutrino may be the key.

But the question is, how do you find the heavy neutrinos described in the paper?