The Science Fiction World of Xueba

Pang Xuelin shook his head and smiled: "Professor Qiao, such inert neutrinos do exist in solar neutrinos, but inert neutrinos exist for a short time during the conversion process, and it is difficult for us to observe them by existing means. Have you ever thought about looking for this inert neutrino through the background radiation of the cosmic neutrino? I remember that the cosmic neutrino background observation array deployed in space is controlled by high energy, I need to get from you Get all the data observed by the neutrino background radiation observation array in the past three decades!"

"Cosmic Neutrino Background Radiation..."

Qiao Anhua frowned and muttered to himself.

Similar to cosmic microwave radiation, cosmic neutrino background radiation is composed of residual neutrinos from the Big Bang.

With the continuous improvement of measurement accuracy, in a series of experiments conducted in the past decades, astrophysicists have found that the background radiation temperature of the universe has slight fluctuations in different regions.

These measurements provide the most accurate picture of the age and composition of the universe. Current observations show that there are about 150 neutrinos per cubic centimeter of the neutrino background in the universe, and the temperature is about 2 Kelvin. Anisotropic.

This slightly different anisotropy in each direction exists in all cases, whether it is matter in the early universe or the huge galaxies and galaxy clusters we see today.

"But Professor Pang, the cosmic neutrino background radiation is the same as the cosmic microwave background radiation. Although there are certain ups and downs, this ups and downs are very stable and can basically be regarded as a straight line, and our neutrinos Although the background radiation observation array can measure the neutrino oscillation, it can only be observed that the neutrino periodically changes in the propagation path. Due to the interference of the solar neutrino in our observation array, the observed neutrino in the universe In the sub-background radiation, there is some periodicity, almost every 28 days, which almost coincides with the period of the sun's rotation around its own axis. In this case, the neutrino background radiation that we actually observed exists. Great deviation, want to find evidence of the existence of lazy neutrinos in these data, is this... is this possible?"

Pang Xuelin said with a smile: "Professor Qiao, have you ever thought that neutrinos have a static mass, and this periodicity is caused by the unequal magnetic field of the sun. The change in the magnetic field strength causes some of the neutrino flow to shift seriously , What I need is precisely the data generated by this severely shifted neutrino stream!"

Qiao Anhua's eyes widened: "Professor Pang, do you mean?"

Qiao Anhua vaguely captured Pang Xuelin's idea.

Pang Xuelin smiled faintly: "Whether it is an electron neutrino, a muon neutrino, or a tau neutrino, their mass does not exceed 1.1 electron volts, and it is less than one half a million of a single electron, but I The inert neutrino mentioned earlier is a heavy neutrino. According to the data I calculated, the upper limit of the mass of inert neutrinos should reach 200 electron volts, which is higher than the remaining neutrinos. There are two orders of magnitude. Regardless of whether in the background radiation of the neutrino in the universe or in the radiation of the solar neutrino, the conversion between the electric neutrino, the mu neutrino, and the τ neutrino occurs every moment, That is to say, a lot of inert neutrinos are mixed in these three kinds of neutrinos, because of our observation methods, we can't distinguish the existence of such inert neutrinos from these kinds of neutrinos. But As long as we can accurately measure the angle data of the solar neutrino flow in the background radiation of the cosmic neutrinos, we can determine the mass of the solar neutrino jet and compare the theoretical mass with the actual observed mass. Such inert neutrinos, then the mass of the solar neutrino flow is probably far beyond our estimates!"

Qiao Anhua's eyes grew bigger and bigger, even a little horrified.

Although in the past six months, Pang Xuelin's level has long spread in academia, even in the field of mathematics, Pang Xuelin also helped the scientific community to solve several heavyweight conjectures.

But Qiao Anhua never thought that Pang Xuelin even had this level in the field of basic physics.

Faintly, Qiao Anhua even felt sour.

He is very clear that if the data observed by the neutrino background radiation of the universe is consistent with what Pang Xuelin predicted, then basic physics will definitely move forward one step forward, and this young man will also leave a strong color in the history of physics pen.

For him, the Nobel Prize in Physics is more like a search for objects.

"Professor Pang, wait a moment, I will go to the data center to get the data immediately!"

Pang Xuelin nodded, watching Qiao Anhua trotting out of the office all the way.

Half an hour later, Pang Xuelin got all the data observed by the neutrino background radiation array of the universe for the past three decades from Qiao Anhua.

In the next three months, Pang Xuelin entered the closed state again.

Thirty years of data, the size is more than a full 30TB, if it is not through the transformation of genetically optimized pharmaceuticals, it will take a few years for Pang Xuelin to analyze these data alone.

But now, for him, analyzing data is pediatrics, and the most important thing is how to get the information he wants from these data.

This kind of research is like finding a needle in a haystack, but Pang Xuelin is very excited.

In the world that I traversed in the past, for various reasons, Pang Xuelin has seen a lot of black technology, and has also learned a lot of cutting-edge knowledge in the field of physics and chemistry. However, this is the first time that independent research is done.

[A large number of photons produced in the Big Bang are left behind after the end of the Big Bang, and the redshift cools as the universe expands, forming the cosmic microwave background radiation we observe today.

Similarly, a large number of neutrinos produced during the Big Bang are also left behind, forming the background of the universe's neutrinos. 】

[The temperature and density in the early universe are very high, so neutrinos and other particles such as baryons, positrons, electrons, and photons interact fully to form a thermal equilibrium fluid, and neutrinos can be transformed with other particles. The distribution of neutrinos conforms to the extremely relativistic Fermi distribution. For an extremely relativistic particle, its quantity and mass density are n=[3/4]F*ζ(3)/π^2*gT^3, ρ=[7/8]F*π^2/30* gT^4……】

[Where T is the temperature, g is the degree of freedom, and ζ is the Riemann Zeta function. For fermions, the factor with the subscript F in front is applied. For bosons, this factor is equal to 1. As the universe expands, the rate of weak interaction reactions decreases rapidly (~T5), making it difficult to maintain the thermal balance of neutrinos and other particles. When weak interaction reaction rate Γ

[However, shortly after the decoupling of neutrinos, a large number of positrons and negative electrons existing in the early universe were annihilated into photon pairs, which caused the temperature of the photon gas to drop.

It is slower than neutrino for a period of time. A simple approximation is to consider the entropy of the system in this process: before the annihilation of the positron-electron pair, the photon, positron, and negative electron each have two spin states, and the fermion needs to be multiplied by a factor of 7/8, so The total effective degree of freedom is g*si=2γ+(2e-+2e+)*7/8=11/2】

[After the annihilation of the positive and negative electrons, the corresponding entropy is transferred to the photon with a degree of freedom of 2. The total entropy does not change in this process, then Tf=(11/4)^1/3*Ti, and the relationship between the final photon gas temperature and the neutrino gas temperature is Tv=(4/11)^1/3* Tγ】

[The temperature of the cosmic microwave background radiation today is 2.725K, so if the neutrino is a massless particle, its temperature today will be 1.945K. In fact, due to the mass of neutrinos, the temperature has to drop even lower. The neutrino oscillation phenomenon indicates that the mass of the neutrino is not zero, but this mass has not been measured. The number density of each neutrino (including positive and negative particles) today is about 112cm-3, according to which the relative density of today's neutrinos is Ων=Σmν/(93.8h2eV). 】

...

[The period of decoupling of neutrinos is also the beginning of the Big Bang nuclear synthesis. During this period, baryons in the universe mainly existed in the form of protons and neutrons. After that, protons and neutrons form deuterium nuclei through nuclear reaction, and then continue to produce tritium (3H), helium 3 (3He), helium 4 (4He), etc. Because the binding energy of deuterium is low, and the number of baryons is much smaller than that of photons, deuterium is easily destroyed by a small number of photons with high energy in a large number of black body radiation photons. Therefore, although deuterium is the product of the direct reaction of proton neutrons, the amount formed in the end Not much, its abundance mainly depends on baryon number density, stable helium is formed more, and its abundance is related to baryon number density and expansion rate. 】

[Neutrinos do not directly play an important role in this process, but mainly affect the expansion rate of the universe. Each relativistic particle contributes part of the density of the universe, and the total density is proportional to the effective relativistic degree of freedom g*. In the standard model of particle physics, there are 3 generations of neutrinos. If we consider the existence of non-standard model neutrino g*=10.75+7/4ΔNν, where 10.75 is the effective relativistic degree of freedom given by the standard model during the Big Bang nuclear synthesis period, and ΔNν represents the light neutrino beyond the standard model The type of “light” here means that the mass of neutrinos is much lower than the temperature during the nuclear synthesis of the Big Bang (~0.1MeV) and can therefore be regarded as extreme relativistic particles. Given the Hubble expansion rate H0 we observed today, the greater the density of the universe, the higher the expansion rate of the universe during nuclear synthesis. 】

[The higher the expansion rate of the universe, the shorter the corresponding time scale for reaction. The effect on the original helium abundance is approximately ΔY=0.013ΔNν. Therefore, according to the original helium abundance, the number of neutrinos in the universe can be limited. People speculate that there are only three neutrinos. Considering that the actual neutrino decoupling process is not instantaneous, the standard value is often taken. Nν=3.046. However, the measurement accuracy of helium abundance is limited, and the original helium abundance must be extrapolated from the measured helium abundance in the ionization zone outside the river. In recent years, the measured value of the original abundance of helium is larger than in the past, and the current measured values ​​range from 0.246 to 0.254, and the difference is greater than the statistical error. In addition, there is degeneracy of Nν and baryon number density, which also limits the accuracy of this method. From the abundances of deuterium and helium, it can be concluded that the number of neutrinos is limited to 1.8

[In fact, the limitation given by this method is not limited to neutrinos, any "dark radiation" component can be restricted. A zero-mass boson in thermal equilibrium with a neutrino at the time of a big explosion can be equivalent to 4/7~=0.57 neutrinos. The zero-mass boson decoupled earlier before the annihilation of positive and negative muons (T~100MeV) can be equivalent to 0.39 neutrinos. 】

...

For three months, Pang Xuelin did not step out of his room.

If you are hungry, someone will naturally bring in food.

Sleepy after falling asleep.

As for bathing or something, that doesn't exist.

If before, Pang Xuelin had a certain purpose when studying other subjects besides mathematical accidents, this time, his research should be purely more.

For the first time from the study of basic physics, he found fun similar to studying mathematics.

This process of looking for material origin through the perspective of God made him feel a pure joy.

It wasn't until three months later that Pang Xuelin's closed door suddenly opened.

In addition to Qiao Anhua, Shen Yuan appeared in front of Pang Xuelin!

"Professor Pang, how is it? Have you found what we need?"

Qiao Anhua stared at Pang Xuelin without blinking.

Pang Xuelin smiled slightly and said, "Do not disgrace the mission!"

Qiao Anhua and Shen Yuan looked at each other, and they both saw a look of excitement in each other's eyes.

Qiao Anhua's excitement lies in the fact that research in the field of neutrinos has finally made breakthrough progress after a stagnation for decades.

Shen Yuan’s excitement is that the emergence of inert neutrinos is likely to allow humans to make breakthroughs in the field of neutrino detection.

And this breakthrough will provide a basis for saving the tranquility deep in the trapped ground.

"Alin, it's been three months since you saw you. You didn't take care of yourself. The whole person stinks. You go to take a shower first and cut your hair by the way. Then we will meet again!"

Shen Yuan told Pang Xuelin.

Pang Xuelin raised his arm and smelled it, said: "Teacher, I don't seem to smell anything!"

Shen Yuan couldn't help crying: "It's strange that you can smell it by yourself, hurry and wash it, and say it after washing!"

"Oh!"

Pang Xuelin smiled and returned directly to his room.

Half an hour later, Pang Xuelin, with shaggy hair, appeared in the conference room of the Institute of High Energy Physics.

At the meeting, in addition to Qiao Anhua and Shen Yuan, there were two other academicians from the Institute of High Energy Physics, Ji Qingqing and Liu Xu, and Cao Guangyun, director of the Daya Bay Neutrino Laboratory of the Chinese Academy of Sciences, and Wang Chongqing, a professor of theoretical physics at Tsinghua University.

Before the meeting started, Pang Xuelin first shared his achievements of the past three months with everyone present, and then said: "Hello everyone, welcome everyone to participate in our internal academic report. For the past three months, I I obtained the neutrino cosmic background radiation observation array data of the past three decades and analyzed it carefully. Finally, based on these data, I can basically determine that there is a fourth type of inert mesomicron in our universe. Neutrino. This kind of neutrino will become a strong candidate for warm dark matter, and it will also have a very important impact on the evolution of our universe."

"Next, I will show you the evidence of the existence of this kind of neutrino. As we all know, the early period of the universe is a period of radiation, and in today’s universe, extreme relativistic particles such as photons and neutrinos with almost negligible density are radiating. The main period is the main contributor to the density of the universe. Radiation-matter equal occurs when the red shift is about 3200, and then the universe is dominated by matter, but by the recombination period (red shift is about 1100), neutrinos still have a significant density contribution."

"If there are more types of neutrinos, it will affect the expansion rate of the universe during the recombination period, and in turn affect the age of the universe during the recombination period, the scale of diffusion, the size of the sound wave horizon, etc. These are the temperature of the cosmic microwave background radiation (CMB) And the polarization anisotropy angular power spectrum appears, the total effect of more neutrinos is to move the so-called damping tail in the CMB angular power spectrum to a larger scale. Comprehensive Hubble constant measurement and WMAP, In the CMB data of ACBAR, ACT, SPT and other experiments, a large attenuation was measured once when the value of l was between 1000 and 3000, and the effective degree of freedom Neff>3..."

"However, the latest neutrino array satellite data gives Neff very close to 3: Neff=3.13±0.32, Planck satellite TT+lowP; Neff=3.15±0.23, Planck satellite TT+lowP+BAO; Neff=2.99±0.20, Planck satellite TT, TE, EE+lowP; Neff=3.04±0.18, Planck satellite TT, TE, EE+lowP+BAO. Here Planck satellite TT, TE, EE refers to It is the temperature and E-type polarization (TT, TE, EE) autocorrelation and cross-correlation angular power spectrum measured by Planck, lowP refers to the polarization data of l<29, BAO refers to the comprehensive 6dF, SDSS, BOSS, WiggleZ, etc. The baryon sound wave oscillations measured by survey data from large-scale structures (03 may still appear..."

...

Pang Xuelin's tone was unhurried, and everyone in the conference room focused on the young man.

In addition to Shen Yuan, the remaining few are all top-level figures in the field of domestic physics.

Needless to say, Qiao Anhua, academician of the Chinese Academy of Sciences, has long been engaged in high-energy physics experiment research, and the Chinese leader of the Geosynchronous OrbitCollider international cooperation project.

Ji Qingqing, academician of the Chinese Academy of Sciences, nuclear physics and high-energy physicist, mainly engaged in nuclear physics, particle physics, high-energy experimental physics, etc., gave a satisfactory explanation for the weak electric symmetry breaking in the standard model, although his theory still It has not been proved, but it has won him widespread praise in the international physics community. Many physicists have tried to further improve the standard model based on his theory.

Liu Xu, an important pioneer in the study of loop quantum gravity, has caused widespread international attention in the study of non-perturbative quantum gravity of spin-junction loops (with spin bubbles).

Cao Guangyun, in addition to the identity of the Daya Bay Neutrino Laboratory of the Chinese Academy of Sciences, he also led the team to successfully determine the magnitude relationship between (Δm21)^2 and (Δm32)^2 in the neutrino oscillation, making the neutrino oscillation In the research, only one theoretical CP destruction phase angle δCP needs to be measured.

In the past three months, while Pang Xuelin was analyzing the neutrino radiation observation satellite array, Qiao Anhua was not idle. He sent Pang Xuelin's theoretical calculation paper and the inert neutrino conjecture to many heavyweight scholars in the circle and asked them Opinions and ideas.

Pang Xuelin's conjecture has caused widespread controversy in the physics community, with some supporting and some opposing.

Of course, the final result depends on whether Pang Xuelin can obtain favorable evidence from the data of the satellite array of neutrino background radiation observation in the universe.

This is also the reason why these big brothers attended this report today.

They are well aware that once Pang Xuelin's theory is confirmed, human research in the field of neutrinos and dark matter will take a big step forward.

The Chinese physics community will once again welcome a trophy for the Nobel Prize in Physics!

...

"The most precise measurement of neutrino mass available now comes from large-scale structural surveys. Photons and plasma are closely coupled to form baryon-photon fluids, while weakly interacting particles such as neutrinos and cold dark matter particles can It travels freely in it. However, the speed of movement of the cold and dark matter particles is almost completely negligible, so the main role is to provide gravitational potential, and neutrinos still have a very high speed of movement during this period, mainly showing diffusivity , Which results in a low power spectrum pressure on a small scale below kn≈0.026(mv/leV)^1/2Ωm^1.2hMpc^-1, the degree is ΔPlin(k)/Plin(k)~-8Ωv/Ωm. Using this effect, if you can accurately measure the shape of the power spectrum, combined with CMB observations, you can limit the mass of neutrinos. Generally, the observable effect mainly depends on the total mass of neutrinos Σmν, but when Σmν is small, strictly It is also related to the quality of a single neutrino."

"A problem here is that most of the density fluctuations in the universe come from dark matter that cannot be directly observed. We have no way to directly measure the density power spectrum of matter, but can only speculate on the density power spectrum through tracers (such as galaxies or intergalactic media) Modern large-scale structural theory holds that galaxies and their dark matter halos are formed at higher material densities, and the relative density of their distribution is proportional to the relative density of matter on a larger scale, that is, δg=bδ, where δg(x)=ng(x)-ng/ng, δ(x)=ρ(x)-ρ/ρ......"

"Ng is the density of galaxies, ρ is the density of matter, and b is the partiality factor. On a larger scale, b is a constant for galaxies with similar properties. In this way, the power spectrum of the star coefficient density is Pgg(k)=b2P( k). This assumption is theoretically reasonable and has been confirmed by some observations-although the power spectrum of various types of galaxies has different bias factors, the power spectrum has roughly the same shape. Another problem is At a small scale related to neutrino mass measurement, density fluctuations have undergone a certain degree of nonlinear evolution. Therefore, when using observations for precise limitation, it is necessary to compare the observation data with the numerical simulation results of different model parameters."

...

Time passed by one minute and one second, and unconsciously, Pang Xuelin's report came to an end.

"Combining various parameters, we can conclude that the mass of solar neutrino jets we observe is two orders of magnitude higher than the theoretical value. There are also many astronomical observations, which are also in line with the theoretical expectations of inert neutrinos. From this, we can be sure that inert neutrinos do exist, and it is very likely to be the warm dark matter we have been looking for!"

The conference room was quiet and no one spoke.

Pang Xuelin smiled faintly: "Do you have any questions?"

Physics is still different from mathematics. As long as mathematics is correct inference, it is basically intact logically.

In physics, no matter what theory, even if it is very consistent with the theory, it needs a lot of evidence to support each other, until there is no problem, it will not be widely recognized by the physics community.

This is like the theory of neutrino oscillation proposed by Soviet physicists Bruno Pontecway and Vladimir Glybov in 1969. When this idea was first proposed, it did not get most of the physics The acceptance of the scientist.

But as time went on, more and more evidence began to lean towards the existence of neutrino oscillations.

This new physics beyond the standard model framework was approved by the physics community.

The theory of inert neutrinos proposed by Pang Xuelin is the same. Even if he has presented enough evidence, it is still difficult to get full approval from everyone present.

At this time, Ji Qingqing took the lead in saying: "Professor Pang, it is undeniable that your theory and the evidence submitted are very convincing, but here, I have a few questions."

"Professor Ji, please!"

"As far as I know, although the measurement accuracy of the satellite power spectrum of the neutrino background radiation observation array of the universe is quite high. From the neutrino oscillation experiment, we can know that the maximum mass in the neutrino exceeds at least 0.04eV. The sub-mass limit is close to this size. However, a problem here is that although the bias factor can generally be used as a constant, this assumption may still be invalid at higher accuracy. If the bias factor has a slight scale dependence, That is, b is not a constant but b(k), which may cause a large error in the neutrino mass measurement. How did you solve this problem?"

Pang Xuelin smiled and said, "It's very simple. We can measure the mass of neutrinos in several different ways. By comparison, we can get the error in the data of the neutrino satellite observation array. For example, as the universe expands, neutrinos The thermal velocity dispersion of the gradual decrease gradually, and the large-scale structure of the uneven material will cause the neutrino to obtain a larger local velocity-this is because the neutrino itself has a small mass and a large velocity dispersion, so the gravitational force experienced in its propagation The field average value is different from ordinary cold dark matter, which leads to the relative velocity between neutrino and dark matter. And the existence of this relative velocity leads to the existence of dipole moment in the neutrino density correlation function or power spectrum. The density itself cannot be directly observed, but the density of neutrinos and dark matter will have different effects on different types of galaxies. Therefore, the dipole moment of the above-mentioned neutrino distribution can be measured by observing the dipole moment of the cross-correlation function of different types of galaxies. Although the cross-correlation function measured in this way also depends on the bias factor, the magnitude of the dipole moment is not sensitive to the bias factor, thus providing an excellent measure of neutrino mass. In addition, nonlinear structures such as dark matter halo A neutrino trail is generated, which also has a dipole moment, which can be statistically observed through a weak gravitational lens in the future."

Ji Qingqing pondered for a moment, a smile appeared on his face: "You have a good idea!"

At this time, Cao Guangyun also said: "Professor Pang, the current larger surveys include the Sloan Digital Survey (SDSS) and its subsequent BOSS, eBOSS and other surveys, and WiggleZ survey. SDSS 7th release data (DR7) The red shift distribution data of the observed bright red galaxies (LRG) are given. The star formation rate of these galaxies is higher and bluer. Although the continuous spectral luminosity is not very high, it is easy to carry out red because of the significant emission line spectrum. Shift measurement. The neutrino mass limit obtained by combining these large-scale structures and CMB data is 95% limited. And the limit is slightly weaker but does not change much after adding the gravitational lens effect. In your paper, the data of the galaxy gravitational lens is also It can be used to limit the power spectrum and neutrino mass, but the current galaxy gravitational lens data is still inaccurate and its results conflict with other observations. How did you solve this problem?"

Pang Xuelin didn’t panic and hurriedly smiled: "Professor Cao, you can turn to the thirteenth page of the thesis, you can see that the limit given by SDSSLRG is more than WiggleZ

Slightly stronger, although the latter has a larger sky survey effective volume. I think this is because the area of ​​the SDSSLRG sky survey is more regular, its window function is sharper, the correlation of the measurement results of different wave number k is smaller, and the window function of WiggleZ is wider. After combining all the data, the strongest limit given is Σmν<0.11eV (95%.). In addition to galaxies, when people observe high-redshift quasars, Raman α absorption line clusters can be seen in their spectra. This is a small amount of photons contained in the ionized intergalactic medium at different redshifts in the propagation path. The formation of neutral hydrogen absorption, commonly referred to as Raman alpha forest, which reflects the distribution of intergalactic media, provides

Another means of measuring fluctuations in the density of matter on related scales. The Raman alpha line itself is in the ultraviolet band and is affected by the Earth’s atmospheric absorption. The low-redshift quasar Raman alpha absorption line is difficult to observe on the ground, but 2.1

The meeting room was quiet again, and after a while, no one spoke.

Qiao Anhua said: "Does anyone have any questions?"

Everyone shook their heads.

Qiao Anhua said with a smile: "Well, Professor Pang, I have one last question. It is undeniable that your paper uses the method of measuring the neutrino background radiation of the universe to measure the mass of the solar neutrino jet. The data obtained is really very It fits your theoretical model. But this method is still an indirect proof method. I want to ask if there is a more direct way to prove the existence of lazy neutrinos!"

Qiao Anhua's voice fell, and there was a sudden commotion in the conference room.

Cao Guangyun said with a smile: "Old Qiao, you have raised your question a little bit. If you can find a more direct measurement method, then Professor Pang's inert neutrino theory is almost nailed down..."

Qiao Anhua smiled without speaking.

Everyone immediately focused on Pang Xuelin.

Pang Xuelin said with a smile: "Professor Qiao, in fact, this is exactly what I want to say next. In the past three months, in addition to collating the observation data of the neutrino array, I was thinking about whether there is a better way to prove inertia. The existence of neutrino, and really found it for me."

"any solution?"

As soon as Pang Xuelin said this, there was a commotion in the meeting room again.

Even Shen Yuan, who had not spoken for a long time, also showed a trace of consternation.

Pang Xuelin said with a smile: "I don't know if you have heard of the double beta decay of neutrinos?"

"Double decay without neutrinos?"

Everyone's face changed in the conference room.

Pang Xuelin said with a smile: "You should remember that Pauli invented the neutrino tangled in 1930 to explain the continuous energy spectrum of the beta decay? The decay of a neutron in the nucleus into a proton is called beta decay. If there are two neutrons The decay that turns into two protons at the same time is called double β decay, which seems not difficult to understand. But Pauli told us that every β decay should be accompanied by a neutrino, so the double β decay should be double neutrino Is it true with the double beta decay? But later, physicists found that although most of the double beta decay appeared a pair of neutrinos, there were also double beta decay without neutrinos in the experiment. Years have passed, haven't you found a reasonable explanation for this phenomenon?"

As soon as Pang Xuelin said these words, Qiao Anhua, Cao Guangyun, Ji Qingqing, Liu Xu and others showed shocked expressions on their faces.

Qiao Anhua said: "Professor Pang, you mean that the so-called double-beta decay without neutrinos does not mean that no neutrinos are produced, but a pair of inert neutrinos that we cannot observe, so the so-called No neutrino double beta decay?"

Pang Xuelin nodded with a smile, and said, "Let’s start with the impenetrable neutrino. We know that the Dirac equation is a field equation describing Fermions, and the positron is a negative energy in the Dirac electron ocean. Hole. In 1937, the Italian talented young physicist Majorana was dissatisfied with the asymmetry between electrons and positrons in the Dirac equation, and combined the fields of positive and anti-particles into one satisfying both positive and anti-particles. The symmetry and the field of the Dirac equation, the corresponding particles are the so-called Mayorana fermions, which are their own antiparticles. Mayorana proposed in the article that neutral neutrinos may be this new Of the Majorana fermions."

"In 1938, the promising Mayorana disappeared mysteriously, and no one has ever seen him again. Whether the neutrino is Dirac fermion or Mayorana fermion has since become a public case. In the ordinary beta In decay, whether it is Dirac or Majorana theoretical electrons must be accompanied by anti-neutrinos, and there is no difference in observations. In 1939, Fury of Harvard University proposed that by looking for neutrino-free double beta decay Judgment on the nature of neutrinos, that is, to find the final state reaction with only two electrons and no neutrinos in the double β decay. The principle of this reaction is: a nucleus with an atom number A and a charge number Z occurs at once (A, Z) → (A, Z+2) +e-+e-+v-e+ve reaction, because this reaction is required to occur at one time, it is necessary to ensure the intermediate state nucleus ~www.readwn.com~ is An imaginary state, that is, its nuclear mass is larger than that of the parent nucleus (A, Z), the first beta decay will not occur. However, the double beta decay without neutrino requires the first beta decay to release a virtual middle The neutrino is absorbed in the second β decay, so that it forms a double beta end state without neutrinos. This reaction can only occur if the neutrino is a Majorana particle. There are three natural nuclei that meet this condition. More than a dozen. Interestingly, the neutrino-free double-beta decay predicted earlier was easier to occur than ordinary double-beta decay, and its half-life was around 1015 years."

"But now, I think we have a more reasonable explanation. In the double beta decay, the so-called first beta decay releases a virtual neutrino to be absorbed in the second beta decay. We might as well say the first An inert neutrino is produced in the beta decay. In the second beta decay, this inert neutrino is converted into another neutrino, which is absorbed by the second beta decay, so no neutrino is formed. Double beta final state. As far as the experiment proves, I think this is not difficult?!"

Qiao Anhua said with a smile: "This is not difficult, and my next doctoral student can do it!"

Cao Guangyun got up and said: "Old Qiao, what are we waiting for, we will go to the laboratory now!"

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