The Science Fiction World of Xueba

Pang Xuelin shook his head and smiled: "Professor Qiao, such inert neutrinos do exist in solar neutrinos, but in the process of transformation, inert neutrinos exist for a short time, and it is difficult for us to observe them through existing means. But Have you ever thought about searching for this kind of inert neutrinos through the cosmic neutrino background radiation? I remember that the cosmic neutrino background observation array deployed in space is controlled by high energy, I need to get from you Access to all the data observed by the Neutrino Background Radiation Observatory Array for the past thirty years!"

"Cosmic neutrino background radiation..."

Qiao Anhua frowned and muttered to himself.

Like cosmic microwave radiation, the cosmic neutrino background radiation is made up of neutrinos left over from the Big Bang.

As measurements have become more precise, astrophysicists have discovered tiny fluctuations in the temperature of the cosmic background radiation in different regions in a series of experiments conducted over the past few decades.

These measurements provide the most precise picture yet of the age and composition of the universe, and current observational data show that the cosmic neutrino background has about 150 neutrinos per cubic centimeter, is about 2 Kelvin in temperature, and is as diverse as the microwave background. Anisotropic.

This slightly different anisotropy in each direction exists in all cases, from matter in the early universe to the massive galaxies and galaxy groups we see today.

"But Professor Pang, the cosmic neutrino background radiation is just like the cosmic microwave background radiation. Although there are certain fluctuations, the fluctuations are very stable and can basically be regarded as a straight line, and our neutrinos Although the background radiation observation array can measure neutrino oscillations, it can only observe periodic changes of neutrinos in the propagation distance. Due to the interference of solar neutrinos in our observation array, the observed cosmic neutrinos In the sub-background radiation, there is a certain periodicity, almost a cycle every 28 days, which almost coincides with the cycle of the sun’s rotation around its own axis. In this case, the neutrino background radiation we actually observe exists If you want to find evidence of the existence of sterile neutrinos in these data, 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 of the magnetic field strength makes some neutrinos flow seriously shifted." , what I need is precisely the data generated by this severely deflected neutrino flow!"

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

Qiao Anhua seemed to have vaguely captured Pang Xuelin's thoughts.

Pang Xuelin smiled lightly: "Whether it is an electron neutrino, a muon neutrino, or a tau neutrino, their mass does not exceed 1.1 electron volts, which is less than one half a millionth of a single electron. The inert neutrino just mentioned,

But it is a kind of heavy neutrino. According to the data I calculated, the upper limit of the mass of inert neutrinos should reach 200 electron volts, which is two orders of magnitude higher than that of the remaining neutrinos. And no matter in the cosmic neutrino background radiation or solar neutrino radiation, the transformation among electron neutrinos, muon neutrinos and tau neutrinos is happening every moment, that is to say, a large number of neutrinos The inert neutrinos are mixed in these three types of neutrinos, because of our observation methods, we have no way to distinguish the existence of this kind of inert neutrinos from these types of neutrinos. However, as long as we can accurately measure the offset angle data of the solar neutrino flow in the cosmic neutrino background radiation, we can determine the mass of the solar neutrino jet, and compare the theoretical mass with the actually observed mass. As long as such inert neutrinos exist, the mass of the solar neutrino flow may far exceed our estimation! "

Qiao Anhua's eyes widened wider and wider, even a little shocked.

Although in the past six months, Pang Xuelin's level has long been known in the academic world, and even in the field of mathematics, Pang Xuelin has helped the scientific community solve several heavyweight conjectures.

But Qiao Anhua never thought that Pang Xuelin would have such a level in the field of basic physics.

Faintly, Qiao Anhua even had a sour feeling.

He is very clear that if the observed data of the cosmic neutrino background radiation are consistent with Pang Xuelin's prediction, then fundamental physics will surely advance a big step forward, and this young man will also leave a strong mark in the history of physics. Pen.

To him, the Nobel Prize in Physics is like getting something out of a bag.

"Professor Pang, wait a moment, I'll go to the data center to get the data right away!"

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

Half an hour later, Pang Xuelin got all the data observed by the cosmic neutrino background radiation array in the past 30 years from Qiao Anhua.

In the next three months, Pang Xuelin entered into a state of retreat again.

Thirty years of data, the size exceeds a full 30TB, if it is not modified by gene optimization agents, it will take several 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 seems to be very interested.

Due to various reasons in the worlds he traveled through in the past, although Pang Xuelin has seen a lot of black technology and learned a lot of cutting-edge knowledge in the fields of physics and chemistry, this is the first time that he has done independent research.

[A large number of photons produced in the big bang were left behind after the hot big bang, and redshifted and cooled as the universe expanded, forming the cosmic microwave background radiation we observe today.

Similarly, a large number of neutrinos created during the Big Bang are also left over, forming the cosmic neutrino background. 】

[In the early universe, the temperature and density were very high, so neutrinos interacted sufficiently with other particles such as baryons, positrons and negative electrons, and photons to form a thermal equilibrium fluid, and neutrinos could be transformed into other particles. At this time The distribution of neutrinos conforms to the extremely relativistic Fermi distribution. For an extremely relativistic particle, its number 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 preceded by the subscript F is applicable, and for bosons, this factor is equal to 1. As the universe expands, the rate of weakly interacting reactions drops rapidly (~T5), making it difficult to maintain thermal equilibrium between neutrinos and other particles. When the weak interaction reaction rate Γ

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

Slower than neutrinos for a while. A simple approximation is to consider the entropy of the system in this process: before the annihilation of the electron-positron pair, the photon, positron and electron-negative electron each have two spin states, and the fermions need 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]

[The corresponding entropy is transferred to the photon after the electron-positron pair is annihilated, and the degree of freedom is 2. The total entropy remains unchanged during this process, then Tf=(11/4)^1/3*Ti, the relationship between the temperature of the final photon gas and the temperature of the neutrino gas is Tv=(4/11)^1/3* Tγ]

[The temperature of the cosmic microwave background radiation today is 2.725K, so if neutrinos are massless particles, their temperature today will be 1.945K. In fact, because neutrinos have mass, their temperature drops even lower. The phenomenon of neutrino oscillations suggests that neutrinos have a non-zero mass, but this mass has not yet been measured. The number density of each kind of neutrinos (including positive and antiparticles) today is about 112 cm-3, according to which the relative density of neutrinos today can be obtained as Ων=Σ mν/(93.8 h2 eV). 】

...

【The period of decoupling of neutrinos is also the period of the beginning of big bang nucleosynthesis. During this period, baryons in the universe mainly existed in the form of protons and neutrons. After that, protons and neutrons form deuterons through nuclear reactions, and then continue to react to generate tritium (3H), helium 3 (3He), helium 4 (4He) and so on. Due to the low binding energy of deuterium, and the number of baryons is much smaller than that of photons, deuterium is easily destroyed by a small number of photons with higher energy in a large number of black body radiation photons, so although deuterium is the product of the direct reaction of protons and neutrons, the final amount formed Not much, its abundance mainly depends on the baryon number density, stable helium is more formed, 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. Every relativistic particle will contribute part of the universe density, 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 neutrinos g*=10.75+7/4 ΔNν in the non-standard model, here 10.75 is the effective relativistic degree of freedom in the big bang nucleosynthesis period given by the standard model, and ΔNν represents the slight, medium, and micro Here, "light" means that the mass of neutrinos is much smaller than the temperature (~0.1MeV) during the nucleosynthesis period of the big bang, so they can be regarded as extremely relativistic particles. Given the Hubble expansion rate H0 observed today, the greater the density of the universe, the higher the expansion rate of the universe during the nucleosynthesis period. 】

[And the higher the expansion rate of the universe, the correspondingly the shorter the time scale available for the reaction, the effect on the original helium abundance is, approximately, ΔY=0.013ΔNν. Therefore, according to the original helium abundance, the number of neutrinos existing in the universe can be limited, and people speculate that there are only three types of 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 abundance of helium must be extrapolated from the measured helium abundance in the extragalactic ionization region. In recent years, the measured value of the original abundance of helium is larger than in the past, and the current measured value ranges from 0.246 to 0.254 , and the difference is greater than the statistical error. In addition, the degeneracy of Nν and baryon number density also limits the accuracy of this method. From the deuterium and helium abundances, it follows that the neutrino population limit is 1.8

[Actually, the confinement given by this method is not limited to neutrinos, any "dark radiation" component can be constrained. A zero-mass boson that was in thermal equilibrium with neutrinos at the time of the Big Bang can be equivalent to 4/7 ~= 0.57 neutrinos. The zero-mass bosons decoupled earlier before the annihilation of pros and cons muons (T~100MeV) can be equivalent to 0.39 neutrinos. 】

...

For three whole months, Pang Xuelin never stepped out of his room.

If you are hungry, someone will bring food in.

Sleepy, fall asleep.

As for taking a shower or something, that doesn't exist.

If before, Pang Xuelin had a certain purpose in researching other subjects except mathematics, then this time, his research was much purer.

For the first time, he found the same pleasure as studying mathematics from the research of basic physics.

This process of finding the source of matter through the perspective of God made him feel a kind of pure joy.

It was not until three months later that Pang Xuelin's closed door suddenly opened.

Apart from Qiao Anhua, Shen Yuan appeared in front of Pang Xuelin!

"Professor Pang, how's it going? Have you found what we need?"

Qiao Anhua stared at Pang Xuelin without blinking.

Pang Xuelin smiled slightly and said, "Fulfill your mission!"

Qiao Anhua and Shen Yuan looked at each other, and they both saw a trace 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 a breakthrough after decades of stagnation.

Shen Yuan's excitement lies in the fact that the appearance of inert neutrinos is likely to allow human beings to make breakthroughs in the field of neutrino detection.

And this breakthrough will provide the basis for rescuing the silence trapped deep in the heart of the earth.

"Alin, look at you. It's been three months and you haven't taken care of yourself. Your whole body stinks. You should take a shower first and cut your hair. We'll meet up and discuss it later!"

Shen Yuan said to Pang Xuelin.

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

Shen Yuan couldn't laugh or cry and said: "It's no wonder you can smell it yourself, hurry up and wash it, and we'll talk after it's done!"

"oh!"

Pang Xuelin smiled and returned directly to his room.

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

In addition to Qiao Anhua and Shen Yuan, two other academicians from the Institute of High Energy Physics, Ji Qingqing and Liu Xu, 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, attended the meeting.

Before the meeting started, Pang Xuelin first shared his achievements in the past three months to everyone present, and then said: "Hi everyone, welcome to our internal academic report meeting. In the past three months, I have learned from the Institute of High Energy I obtained the neutrino cosmic background radiation observation array data in the past thirty years, and analyzed them in detail. Finally, based on these data, I can basically conclude that in our universe, there is a fourth kind of inert neutrino This kind of neutrino will become a strong candidate for warm dark matter, and it also has a very important impact on the evolution of our universe."

"Next, I will show you the evidence for the existence of such neutrinos. As we all know, the early universe was dominated by radiation. In today's universe, extreme relativistic particles such as photons and neutrinos whose density is almost negligible are in the radiation. The dominant period is the main contributor to the density of the universe. The radiation-matter equality occurs at a redshift of about 3200, after which the universe is dominated by matter, but until the recombination period (redshift about 1100), neutrinos still have a significant contribution to the density contribute."

"If there are more neutrino species, it will affect the expansion rate of the universe during the recombination period, and then affect the age of the universe during the recombination period, the scale of diffusion, the size of the sonic horizon, etc., which are in the cosmic microwave background radiation (CMB) temperature and polarization anisotropy angular power spectrum, the overall effect of more neutrinos is to shift the so-called damping tail in the CMB angular power spectrum to a larger scale. Combining Hubble constant measurements and WMAP , the CMB data of ACBAR, ACT, SPT and other experiments once measured a large attenuation when the value of l was between 1000 and 3000, and the effective degree of freedom Neff\u003e3..."

"However, the Neff given by the latest neutrino array satellite data is 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 angle power spectrum measured by Planck, lowP refers to the polarization data of l\u003c29, BAO refers to the comprehensive 6dF, SDSS, BOSS, WiggleZ, etc. The (03 may still appear..."

...

Pang Xuelin's tone was unhurried, and everyone's eyes in the meeting room were focused on this young man.

Except for Shen Yuan, the rest of them are all leading figures in the field of physics in China.

Needless to say, Qiao Anhua is an academician of the Chinese Academy of Sciences, has been engaged in high-energy physics experimental research for a long time, and is the Chinese director of the international cooperation project of the Geosynchronous Orbit Collider (Geosynchronous Orbit Collider).

Ji Qingqing, academician of the Chinese Academy of Sciences, nuclear physics and high-energy physicist, mainly engaged in the research of nuclear physics, particle physics, high-energy experimental physics, etc., gave a satisfactory explanation for the breaking of electroweak symmetry in the standard model, although his theory is still It has not been proved, but he has won wide acclaim in the international physics community, and 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 aroused widespread international attention in the study of spin-netted loop (and spin foam) non-perturbative quantum gravity.

Cao Guangyun, in addition to being the director of the Daya Bay Neutrino Laboratory of the Chinese Academy of Sciences, he also led the team to successfully determine the size relationship between (Δm21)^2 and (Δm32)^2 in the neutrino oscillation, making the neutrino oscillation From the research, only a theoretical CP destruction phase angle δCP is left 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 papers and his conjectures on inert neutrinos to many heavyweight scholars in the circle and asked them opinions and ideas.

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

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

This is also the reason why these bigwigs attended this report meeting today.

They are very clear 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 usher in a Nobel Prize in Physics trophy!

...

"The most precise measurements of neutrino mass available come from the Large Scale Structure Survey. Photons are tightly coupled with plasmas to form a baryon-photon fluid, while weakly interacting particles such as neutrinos and cold dark matter particles can Freely travel through it. However, the motion speed of cold dark matter particles is almost completely negligible, so it mainly plays the role of providing gravitational potential, while neutrinos still have a very high motion speed during this period, mainly showing the diffusion , which leads to a power spectrum depression on small scales below kn≈0.026(mv/leV)^1/2Ωm^1.2hMpc^-1, to the extent of ΔPlin(k)/Plin(k)~-8Ωv/Ωm. Using this effect, if the shape of the power spectrum can be accurately measured and combined with CMB observations, the mass of neutrinos can be restricted. Usually, the observable effect mainly depends on the total mass Σmν of neutrinos, but when Σmν is small, the strict It is also related to the mass of individual neutrinos."

"One 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 only infer the density power spectrum from tracers (such as galaxies or the intergalactic medium) The modern large-scale structure theory holds that galaxies and their dark matter halos are formed at places with higher matter density, 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 called the partiality factor. On a larger scale, for galaxies with similar properties, b is a constant. In this way, the power spectrum of the density of galaxies is Pgg(k)=b2P( k). This hypothesis is theoretically sound and has been confirmed by some observations—the power spectra of various types of galaxies have roughly the same shape, although the bias factors vary. Another question is , on the small scales related to neutrino mass measurements, the density fluctuations have undergone a certain degree of nonlinear evolution, so it is necessary to compare the observed data with the numerical simulation results of different model parameters when using observations for precise constraints."

...

Time passed by, and Pang Xuelin's report came to an end before he knew it.

"Integrating various parameters, we can conclude that the mass of the solar neutrino jet we observed is two orders of magnitude higher than the theoretical value. At the same time, there are also many astronomical observation data, which are also very consistent with the theoretical expectations of inert neutrinos. , from this, we can be sure that the inert neutrinos do exist, and most likely, they are the warm dark matter we have been looking for!"

The meeting room fell silent, no one spoke.

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

There is still a difference between physics and mathematics. As long as there is correct reasoning in mathematics, it is basically impeccable in logic.

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

This is like the theory of neutrino oscillations proposed by Soviet physicists Bruno Pontekov and Vladimir Glibov in 1969. When this idea was first proposed, most physics did not get it. accepted by scholars.

But over time, more and more evidence began to lean toward the existence of neutrino oscillations.

This new physics beyond the framework of the Standard Model has only been recognized by the physics community.

The same is true for the inertial neutrino theory proposed by Pang Xuelin. 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 and said: "Professor Pang, it is undeniable that your theory and the evidence you submitted are very convincing, but here, I have a few questions."

"Professor Ji, please tell me!"

"As far as I know, although the measurement accuracy of the power spectrum of the cosmic neutrino background radiation observation array satellite is quite high. From the neutrino oscillation experiment, it can be known that the maximum mass of neutrinos exceeds 0.04eV at least, and the current neutrino The submass limit is already close to this size. However, a problem here is that although the bias factor can generally be regarded as a constant, at higher precision, this assumption may still be broken. If the bias factor has a small scale dependence, That is, b is not a constant but b(k), which may lead to a large error in neutrino mass measurement. How do you solve this problem?"

Pang Xuelin smiled and said: "It's very simple. We can use several different methods to measure the mass of neutrinos. Through comparison, we can get the size of the error in the neutrino satellite observation array data. For example, as the universe expands, neutrinos The thermal velocity dispersion of the neutrino gradually decreases, and the large-scale structure of the inhomogeneous matter will cause the neutrino to obtain a larger intrinsic velocity—this is because the neutrino itself has a small mass and a large velocity dispersion, so the gravitational force felt during its propagation The field average is different from ordinary cold dark matter, which leads to the existence of relative velocity between neutrinos and dark matter. The existence of this relative velocity leads to the existence of dipole moments in the density correlation function or power spectrum of neutrinos. Although the neutrino’s The density itself cannot be directly observed, but the density of neutrinos and dark matter will have different effects on different types of galaxies, so by observing the dipole moments of the cross-correlation functions of different types of galaxies, the above-mentioned neutrino distribution dipole moments can be measured. Although the cross-correlation function measured in this way also depends on the bias factor, the size 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 halos are also Generate neutrino wakes, which also have dipole moments, and can be statistically observed through weak gravitational lensing in the future."

Ji Qingqing pondered for a moment, then smiled and said, "You have a good idea!"

At this time, Cao Guangyun followed suit and said: "Professor Pang, the current larger sky surveys include the Sloan Digital Sky Survey (SDSS) and its follow-up BOSS, eBOSS and other sky surveys, as well as the WiggleZ sky survey. The seventh release data of SDSS (DR7) The redshift distribution data of the observed luminous red galaxies (LRG) are given. These galaxies have higher star formation rates and are bluer. The neutrino mass confinement obtained by combining these large-scale structure and CMB data is 95%. Confinement. And the confinement is slightly weaker but the change is not large after adding the gravitational lensing effect. In your paper, the galaxy gravitational lensing data are also It can be used to limit the power spectrum and neutrino mass, but the current galactic gravitational lensing data is not accurate and the results it gives have certain conflicts with other observation data, how do you solve this problem?"

Pang Xuelin calmly smiled and said, "Professor Cao, you can turn to the thirteenth page of the paper, and you can see that the limit given by SDSS LRG is higher than that of WiggleZ

Slightly stronger, although the latter has a larger survey effective volume. I think this is because the area of ​​the SDSS LRG sky survey is more regular, its window function is sharper, and the measurement results of different wavenumbers k are less correlated, while the window function of WiggleZ is wider. After combining all the data, the strongest limit given is Σ mν\u003c0.11eV (95%.). In addition to galaxies, when people observe high-redshift quasars, they can see Raman α absorption line clusters in their spectra, which are a small amount contained in the ionized intergalactic medium at different redshifts during the propagation of photons. Formed by the absorption of neutral hydrogen, commonly known as the Raman α forest, which reflects the distribution of the intergalactic medium, providing

Another way to measure the fluctuations in the density of matter on the relevant scale. The Raman α spectral line itself is in the ultraviolet band, affected by the absorption of the earth’s atmosphere, the low redshift Raman α absorption line of quasars is difficult to observe on the ground, but the 2.1

The meeting room fell silent again, and after a while, no one spoke.

Qiao Anhua said, "Do you have any doubts?"

Everyone shook their heads.

Qiao Anhua smiled and said, "Okay, Professor Pang, I have one last question. It is undeniable that your paper uses the cosmic neutrino background radiation observation array to measure the mass of the solar neutrino jet, and the data obtained are indeed very good." It fits your theoretical model. But this method is still an indirect method of proof after all, I would like to ask if there is a more direct way to prove the existence of sterile neutrinos!"

After Qiao Anhua finished speaking, there was a commotion in the conference room.

Cao Guangyun said with a smile: "Old Qiao, you are a bit exaggerating about this question. If you can find a more direct measurement method, then Professor Pang's inertial neutrino theory is almost a certainty..."

Qiao Anhua smiled, but remained silent.

Everyone immediately focused their attention on Pang Xuelin.

Pang Xuelin smiled and said: "Professor Qiao, this is actually what I want to say next. In the past three months, in addition to sorting out the neutrino array observation data, I also wondered if there is a better way to prove inertia. The existence of neutrinos, and I really found them."

"any solution?"

As soon as Pang Xuelin said this, the meeting room became commotion again.

Even Shen Yuan, who had not spoken all this time, showed a look of shock on his face.

Pang Xuelin said with a smile: "I wonder if you have heard of neutrinoless double beta decay?"

"Neutrinoless double-beta decay?"

The expressions of everyone in the conference room changed.

Pang Xuelin said with a smile: "Everyone should remember that Pauli invented the neutrino in 1930 in order to explain the continuum of beta decay? The decay of a neutron into a proton in the nucleus is called beta decay. If there are two neutrons The decay that becomes two protons at the same time is called double beta decay, which seems not difficult to understand. But Pauli told us that every beta decay should be accompanied by a neutrino, so double beta decay should be double neutrinos Accompanied by double-beta decay? But later, physicists discovered that although most double-beta decays have a pair of neutrinos, there are also neutrino-free double-beta decays in experiments. More than a hundred Years have passed, and this phenomenon has not yet found a reasonable explanation, right?"

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, what you mean is that the so-called neutrinoless double-beta decay does not produce neutrinos, but produces a pair of inert neutrinos that we cannot observe, so the so-called neutrinos appear. Neutrinoless double-beta decay?"

Pang Xuelin nodded with a smile, and said: "Let's start with the neutrinos, which are difficult to figure out. We know that the Dirac equation is the field equation describing the fermions, and the positron is the negative energy in the Dirac electron ocean. Holes. In 1937, Italian genius young physicist Majorana was dissatisfied with the asymmetry between electrons and positrons in the Dirac equation, and combined the fields of positive and antiparticles into a field that satisfies both positive and antiparticles. The symmetry and the field of the Dirac equation, the corresponding particles are the so-called Majorana fermions, which are their own antiparticles. Majorana proposed in the article that the neutral neutrino may be this new Majorana fermions."

"In 1938, the promising Majorana disappeared mysteriously, and no one has seen him since. Whether the neutrino is a Dirac fermion or a Majorana fermion has become a public case since then. In ordinary β In the decay, whether it is Dirac or Majorana theory electrons must appear with antineutrinos, there is no difference in observation. In 1939, Fury of Harvard University proposed that the neutrinoless double beta decay can be used to analyze The nature of neutrinos to make judgments, that is to say, to look for the final state reaction in which there are only two electrons and no neutrinos in the double beta decay. The principle of this reaction is: an atomic nucleus with an atomic number A and a charge number Z occurs at a time (A, Z)→(A, Z+2)+e-+e-+v-e+v-e reaction, since this reaction is required to occur at one time, it is necessary to ensure that the intermediate state nucleus (A, Z+1) is A virtual state, which requires its nuclear mass to be larger than the parent nucleus (A, Z), the first β decay will not occur. The neutrinoless double β decay requires the first β decay to release a virtual neutral The neutrinos are absorbed in the second beta decay, so that a double beta final state without neutrinos is formed. This reaction is only possible if the neutrinos are Majorana particles. There are thirty natural nuclei that meet this condition Various. Interestingly, the early predicted neutrinoless double-beta decay occurs much more readily than ordinary double-beta decay, with a half-life of around 1015 years."

"But now, I think we have a more reasonable explanation. In the double beta decay, the so-called first beta decay, a virtual neutrino is emitted and absorbed in the second beta decay. Let's say the first In the beta decay, an inert neutrino is produced. In the second beta decay, this inert neutrino is transformed into another kind of neutrino, which is absorbed by the second beta decay, so no neutrino is formed. Double beta final state. As for the experimental proof, I don’t think it’s too difficult?!”

Qiao Anhua smiled and said, "It's not difficult, a doctoral student under me can do it!"

Cao Guangyun stood up and said, "Old Qiao, what are you waiting for, let's go to the laboratory now!"

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