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

"Cosmic Neutrino Background Radiation ......"

Jo Anhua frowned and muttered to himself.

Similar to cosmic microwave radiation, cosmic neutrino background radiation is made up of the remnants of neutrinos from the Big Bang.

As the accuracy of measurements continues to improve, astrophysicists have found small fluctuations in the cosmic background radiation temperature in different regions in a series of experiments conducted over the past few decades.

These measurements provide the most accurate picture 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, a temperature of about 2 Kelvin, and is as anisotropic as the microwave background.

This anisotropic phenomenon, which is slightly different in each direction, is present in all cases, from matter in the early universe to the vast galaxies and groups of galaxies we see today.

"But Professor Pang, the cosmic neutrino background radiation is the same as the cosmic microwave background radiation, although there are certain fluctuations, but this fluctuation is very stable, basically it can be regarded as a straight line, and although our neutrino background radiation observation array can measure neutrino oscillations, it can only observe the periodic changes of neutrinos in the propagation distance, due to the interference of solar neutrinos in our observation array, resulting in a certain periodicity in the observed cosmic neutrino background radiation, There is a cycle almost every 28 days, which almost coincides with the period of the Sun's rotation around its own axis, and in this case, the neutrino background radiation that we actually observe is very skewed, and it is ...... to find evidence of the existence of inert neutrinos in these data Is this possible?! ”

Pang Xuelin said with a smile: "Professor Qiao, have you ever thought that neutrinos have static mass, and this periodicity is caused by the unequal magnetic field of the sun. The change in the strength of the magnetic field has caused some of the neutrino streams to be seriously offset, and what I need is precisely the data generated by this kind of neutrino flow that has undergone a severe shift! ”

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

Qiao Anhua seemed to vaguely capture Pang Xuelin's thoughts.

Pang Xuelin smiled faintly: "Whether it is an electric neutrino, a μ neutrino, or a τ neutrino, their mass does not exceed 1.1 electron volts, less than one of 500,000 parts of a single electron, but the inert neutrino I just mentioned is a heavy neutrino, according to the data I calculated, the upper limit of the mass of the inert neutrino should reach 200 electron volts, which is two orders of magnitude higher than the remaining neutrinos." Regardless of whether in the cosmic neutrino background radiation or solar neutrino radiation, the transformation between electric neutrinos, μ neutrinos, and τ neutrinos occurs all the time, that is, a large number of inert neutrinos are mixed in these three neutrinos, and we cannot distinguish the existence of such inert neutrinos from these neutrinos because of our observation methods. However, as long as we can accurately determine the offset angle 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 actual observed mass. As long as such inert neutrinos exist, the mass of the solar neutrino stream is far beyond our estimates! ”

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

Although in the past six months, Pang Xuelin's level has long spread in the academic community, 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 this level in the field of basic physics.

Faintly, Qiao Anhua even had a sour feeling.

He knew very well that if the data observed by the cosmic neutrino background radiation were consistent with Pang Xuelin's predictions, then fundamental physics would take a big step forward, and this young man would leave a strong mark in the history of physics.

The Nobel Prize in Physics is like a treasure trove for him.

"Professor Pang, wait a minute, I'll go to the data center to get the data immediately!"

Pang Xuelin nodded, watching Qiao Anhua's figure trot all the way 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 thirty years from Qiao Anhua.

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

Thirty years of data, the size of more than a full 30 terabytes, if it were not for the transformation of genetic optimization drugs, it would take Pang Xuelin several years 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 it.

This kind of research is like looking for a needle in a haystack, but Pang Xuelin seems to be interested.

In those worlds he traveled through in the past, for various reasons, 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 to do research independently.

[A large number of photons produced in the Big Bang were left behind after the end of the hot Big Bang and cooled with the redshift as the universe expanded, forming the cosmic microwave background radiation that we observe today.

Similarly, a large number of neutrinos produced during the Big Bang are left behind, forming the cosmic neutrino background. 】

[In the early universe, the temperature and density were very high, so neutrinos and other particles such as baryons, positrons, photons, etc. all interacted fully to form a thermal equilibrium fluid, and neutrinos could be converted to other particles, and the distribution of neutrinos conformed to the extreme relativistic Fermi distribution. For an extreme 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 degrees of freedom, and ζ is the Riemann Zeta function.] For fermions, the factor with the lower corner mark F in front is applied, and for the boson, the factor is equal to 1. As the universe expands, the reaction rate of weak interactions decreases rapidly (~T5), making it difficult to maintain the thermal equilibrium of neutrinos and other particles. When the rate of weak interaction reaction Γ

[However, shortly after neutrino decoupling, a large number of positive and negative electrons present in the early universe were annihilated into photon pairs, which led to a drop in the temperature of the photon gas

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 positive and negative electron pairs, 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 electron pairs, the corresponding entropy is transferred to the photon with a degree of freedom of 2.] If the total entropy does not change in this process, then Tf=(11/4)^1/3*Ti, and the relationship between the temperature of the final photonic 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 2.725 K, so if the neutrino were a massless particle, its temperature today would be 1.945 K.] In fact, because neutrinos have mass, their temperature drops even lower. The neutrino oscillation phenomenon indicates that the neutrino mass is not zero, but this mass has not yet been measured. The number density of each neutrino (including positive and antiparticles) today is about 112 cm-3, from which the relative density of today's neutrinos is Ων=Σ mν/(93.8 h2 eV). 】

……

[The period of neutrino decoupling is also the period when Big Bang nucleosynthesis begins.] During this period, the baryon in the universe existed mainly in the form of protons and neutrons. After that, protons and neutrons form deuterium nuclei through nuclear reactions, which continue to react to form 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 higher energy in a large number of blackbody radiation photons, so although deuterium is the product of direct reaction of protons and neutrons, the final amount formed is not much, and its abundance mainly depends on the baryon number density, while stable helium is formed more, and its abundance is related to the 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 degrees of freedom g*. In the Standard Model of particle physics, there are 3 generations of neutrinos. If we consider the presence of neutrinos g*=10.75+7/4 ΔNν in the presence of non-standard models, where 10.75 is the effective relativistic degrees of freedom given by the Standard Model during the Big Bang nuclear synthesis, and ΔNν, which denotes the type of light neutrino beyond the Standard Model, where "light" refers to the neutrino mass much less than the temperature (~0.1 MeV) during the Big Bang nuclear synthesis period and can therefore be regarded as extreme relativistic particles. Given the Hubble expansion rate H0 that we observe today, the greater the density of the universe, the higher the expansion rate of the universe during the nuclear synthesis period. 】

[The higher the rate of expansion of the universe, the shorter the time scale available for reaction, which has an effect on the primordial helium abundance, approximately, ΔY=0.013ΔNν.] Therefore, the number of neutrinos in the universe can be limited according to the primordial helium abundance, and it is speculated that only three neutrinos exist, and considering that the actual neutrino decoupling process is not instantaneous, the standard value Nν = 3.046 is often taken. However, the accuracy of helium abundance measurement is limited, and the original helium abundance has to be extrapolated from the measured helium abundance in the extrariver ionization zone. In recent years, the initial abundance of helium has been measured more than in the past, with current measurements ranging from 0.246 to 0.254, and the difference is greater than the statistical error. In addition, there is a degeneracy between Nν and the baryon number density, which also limits the accuracy of this method. From the deuterium and helium abundances, it can be concluded that the limit for the number of neutrinos is 1.8

[In fact, the limits given in this method are not limited to neutrinos, and any component of "dark radiation" can be limited.] A zero-mass boson that was in thermal equilibrium at the same time as a neutrino at the time of the Big Bang is equivalent to 4/7 ~= 0.57 neutrinos. Earlier, before the annihilation of positive and negative μ (T~100 MeV), the zero-mass bosons decoupled can be equivalent to 0.39 neutrinos. 】

……

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

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

When you are sleepy, you fall asleep.

As for bathing or something, that's non-existent.

If before, Pang Xuelin had a certain purpose in his research on other disciplines except mathematics, then this time, his research is much purer.

For the first time, he found a similar pleasure in studying mathematics to the study of fundamental physics.

This process of searching for the source of matter through God's perspective made him feel a pure joy.

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

appeared in front of Pang Xuelin, in addition to Qiao Anhua, there was also Shen Yuan!

"Professor Pang, how's it going? Found what we need? ”

Qiao Anhua stared at Pang Xuelin without blinking.

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

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

Joanne's excitement is that after decades of stagnation, research in the field of neutrinos has finally made a breakthrough.

Shen Yuan's excitement lies in the fact that the emergence of inert neutrinos is likely to allow mankind to make a breakthrough in the field of neutrino detection.

And this breakthrough will provide the foundation for saving Shen Jing who is trapped in the depths of the earth's heart.

"Alin, look at you, it's been three months, you don't take care of yourself, the whole person stinks, you go take a shower first, cut your hair by the way, and then we will meet and discuss!"

Shen Yuan said to Pang Xuelin.

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

Shen Yuan couldn't help but laugh and said: "It's strange that you can smell it yourself, hurry up and wash it, and then talk about it after washing!" ”

"Oh!"

Pang Xuelin smiled and returned directly to his room.

Half an hour later, Pang Xuelin, with his 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, professor of theoretical physics at Tsinghua University, attended the meeting.

Before the start of the meeting, Pang Xuelin first shared his achievements in the past three months with everyone present, and then said: "Hello everyone, welcome to our internal academic report, in the past three months, I have carefully analyzed the neutrino cosmic background radiation observation array data obtained from the high energy institute in the past 30 years, and finally based on these data, I can basically determine that there is a fourth inert neutrino in our universe. Such neutrinos will be a strong candidate for warm and dark matter, and at the same time have a very important impact on the evolution of our universe. ”

"Next, I'm going to show you the evidence for the existence of such neutrinos. As we all know, the early days of the universe were dominated by radiation, and extreme relativistic particles such as photons and neutrinos, whose density is almost negligible in today's universe, were the main contributors to the density of the universe during the radiation-dominated period. Radiation-matter equality occurs at a redshift of about 3200, after which the universe is dominated by matter, but by the recombination period (redshift of about 1100), neutrinos still contribute significantly to density. ”

"If there are more neutrino species, it will affect the rate of expansion of the universe during the recombination period, and then the age of the universe during the recombination period, the scale of diffusion, the size of the acoustic horizon, etc., which are manifested in the cosmic microwave background radiation (CMB) temperature and polarization anisotropy angular power spectrum, and the overall effect of more neutrino numbers is to shift the so-called damping tail in the CMB angular power spectrum to a larger scale. Based on the Hubble constant measurement and the CMB data of WMAP, ACBAR, ACT, SPT and other experiments, a large attenuation was measured at the value of l at 1000 ~ 3000, and the effective degree of freedom Neff > was given3……”

"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's satellite TT,TE,EE refers to Planck's measured temperature and E-type polarization (TT,TE,EE) autocorrelation and cross-correlation angular power spectra, and lowP refers to l<29 polarization data, BAO refers to the baryon acoustic oscillations measured by the survey data of large-scale structures such as 6dF, SDSS, BOSS, WiggleZ (03 may still be ......"

……

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

Except for Shen Yuan, the rest of the people 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 experimental research on high-energy physics for a long time, and is the Chinese leader of the international cooperation project of the Geosynchronous Orbit Collider.

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 and other aspects of research, the standard model in the weak current symmetry break gave a satisfactory explanation, although his theory has not been proven, but has won him wide acclaim in the international physics community, there are many physicists based on his theory to try to further improve the standard model.

Liu Xu, an important pioneer in the study of quantum gravity, has attracted extensive international attention in his research on the non-perturbative quantum gravity of spin junction nets (and spin bubbles).

Cao Guangyun, in addition to the identity of the director 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 neutrino oscillations, so that the study of neutrino oscillations only has a theoretical CP destruction phase angle δCP 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 inert neutrino conjecture to many heavyweight scholars in the circle, asking for their opinions and ideas.

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

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

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

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

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

……

"The most sophisticated measurement of the mass of the existing neutrinos comes from the large-scale structural survey. Photons are tightly coupled to the plasma to form a baryon-photonic fluid, through which weakly interacting particles, such as neutrinos and cold dark matter particles, can travel freely. However, the velocity of cold dark matter particles is almost completely negligible, so it mainly plays a role in providing gravitational potential, while neutrinos still have a very high velocity during this period, mainly exhibiting diffuseness, which leads to a power spectrum depression at a small scale below kn≈0.026(mv/leV)^1/2Ωm^1.2hMpc^-1, to the extent of ΔPlin(k)/Plin(k)~-8Ωv/Ωm. Taking advantage of this effect, the shape of the power spectrum can be accurately measured, combined with CMB observations, to limit the neutrino mass. In general, observable effects depend mainly on the total mass of neutrinos, Σmν, but when Σmν is small, strictly speaking, 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. There is no way to directly measure the density power spectrum of matter, but only to infer the density power spectrum from tracers such as galaxies or intergalactic media. Modern large-scale structure 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 at a larger scale, i.e., 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, b is called the bias factor, and on larger scales, b is a constant for galaxies of similar nature. In this way, the star coefficient density power spectrum is Pgg(k)=b2P(k). This hypothesis is theoretically plausible and has been confirmed by some observations that the power spectrum of different types of galaxies has roughly the same shape, although the bias factor varies. Another problem is that density fluctuations have undergone a certain degree of nonlinear evolution at the small scales associated with neutrino mass measurements, so it is necessary to compare the observational data with the numerical simulation results of different model parameters when using observations for precise limitations. ”

……

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

"Taking all the parameters together, we can conclude that the mass of the solar neutrino jet that we have observed is two orders of magnitude higher than the theoretical value, and there are also many astronomical observations, which are also very consistent with the theoretical expectations of inert neutrinos, from which we can be sure that inert neutrinos do exist, and most likely, they are the warm and dark matter we have been looking for!"

The room fell silent, and no one spoke.

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

Physics is still different from mathematics, as long as it is correct reasoning in mathematics, the logic is basically impeccable.

In physics, no matter what the 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 similar to the neutrino oscillation theory proposed by Soviet physicists Bruno Pontekwe and Vladimir Glibov in 1969, which was not accepted by most physicists when it was first proposed.

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

This new physics, which goes beyond the framework of the Standard Model, has been recognized by the physics community.

The same is true of the inert neutrino theory proposed by Pang Xuelin, even if he has put forward enough evidence, it is still difficult to get the full approval of everyone present.

At this time, Ji Qingqing took the lead and said: "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 speak!"

"As far as I know, although the current measurement accuracy of the power spectrum of the Neutrino Background Radiation Observation Array satellites in the universe is quite high. Neutrino oscillation experiments show that the maximum mass in neutrinos is at least 0.04 eV, and the current neutrino mass limit is close to this size. One problem here, however, is that although the bias factor can generally be used as a constant, this assumption can still be invalid at a higher level of accuracy, and a small scale dependence of the bias factor, i.e., b is not a constant but b(k), can lead to large errors in neutrino mass measurements. How did you solve this problem? ”

Pang Xuelin smiled and said: "Very simply, we can measure the neutrino mass with several different methods, and the magnitude of the error in the neutrino satellite observation array data can be obtained through comparison. For example, as the cosmic expansion of the neutrino's thermal velocity diffusion, the inhomogeneous large-scale structure of matter causes neutrinos to gain a large intrinsic velocity—because neutrinos themselves have a small mass and large velocity dispersion, so the average gravitational field felt during their propagation is different from that of ordinary cold dark matter, which leads to a relative velocity between neutrinos and dark matter. The presence of this relative velocity results in a dipole moment in the neutrino density correlation function or power spectrum. Although the density of neutrinos itself cannot be directly observed, the density of neutrinos and dark matter can have different effects on different types of galaxies, so the dipole moment of the 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 of this measurement also depends on the bias factor, the magnitude of the dipole moment is not sensitive to the bias factor, thus providing an excellent means of measuring neutrino mass. In addition, nonlinear structures such as dark matter halos also produce neutrino trails, which also have dipole moments, which can be statistically observed by weak gravitational lensing in the future. ”

Ji Qingqing pondered for a moment, and said with a smile on his face: "You have a good idea!" ”

At this time, Cao Guangyun also spoke up: "Professor Pang, the current larger surveys include the Sloan Digital Sky Survey (SDSS) and its subsequent BOSS, eBOSS and other Sky Surveys, as well as the WiggleZ Sky Survey. The 7th release data of the SDSS (DR7) gives the redshift distribution of its observed bright red galaxies (LRG). These galaxies have a higher rate of star formation and are bluer, and although the continuum is not very luminous, they are facilitated by significant emission lines that facilitate redshift measurements. Combining these large-scale structures and CMB data, the neutrino mass limit is 95%. Moreover, the restriction is slightly weaker but does not change much after the gravitational lensing effect is added. In your paper, galaxy gravitational lensing data can also be used to limit power spectra and neutrino masses, but how did you solve this problem when the current gravitational lensing data is not accurate and the results given are in conflict with other observations? ”

Pang Xuelin was not in a hurry, and said with a faint smile: "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 SDSS LRG survey has a more regular area, its window function is sharper, and the measurement results of different wavenumber k are less correlated, while the window function of WiggleZ is wider. After combining all the data, the strongest limit given is Σ mν<0.11eV (95%.). In addition to galaxies, when one observes a quasar with a high redshift, a cluster α of Raman absorption lines can be seen in its spectrum, which is formed by the absorption of small amounts of neutral hydrogen contained within the ionized intergalactic medium at different redshifts in the propagation pathway, often referred to as Raman α forests, which reflect the distribution of the intergalactic medium, provide

is another means of measuring the fluctuation of the density of matter on the scale. The Raman α line itself is in the ultraviolet band, which is affected by the absorption of the Earth's atmosphere, and the Raman α absorption line of the quasar with low redshift is difficult to observe on the ground, but 2.1

The room fell silent again, and after a few moments, no one spoke.

Qiao Anhua spoke: "Don't you have any questions? ”

Everyone shook their heads.

Qiao Anhua smiled: "Okay, Professor Pang, I have one last question, it is undeniable that the method of measuring the mass of the solar neutrino jet through the cosmic neutrino background radiation observation array in your paper is indeed very consistent with your theoretical model. But this method is still an indirect proof method after all, and I would like to ask if there is a more direct way to prove the existence of inert neutrinos! ”

Qiao Anhua's voice fell, and a commotion suddenly sounded in the conference room.

Cao Guangyun said with a smile: "Old Qiao, your question is a bit of a lever, if you can find a more direct measurement method, then Professor Pang's inert neutrino theory is almost a certainty......"

Qiao Anhua smiled and didn't say anything.

Everyone immediately focused their attention 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 sorting out the neutrino array observation data, I am also thinking about whether there is a better way to prove the existence of inert neutrinos, and I really found it." ”

"What's the solution?"

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

Even Shen Yuan, who had not spoken, had a trace of surprise on his face.

Pang Xuelin smiled: "I don't know if you have heard of neutrino β decay?" ”

"Neutrino-free binary β decay?"

The faces of everyone in the conference room changed.

Pang Xuelin said with a smile: "Should you remember Pauli's tangled invention of neutrinos in 1930 in order to explain the beta decay continuum? The decay of one neutron into a proton in the nucleus is called β decay, and if two neutrons become two protons at the same time, it is called a two-β decay, which seems not difficult to understand. But Pauli tells us that every β decay should be accompanied by a neutrino, so the β decay should be accompanied by a double neutrino with the decay of the β. But later, physicists discovered that while most β decay occurs in a pair of neutrinos, there is also a neutrino-free β decay in experiments. More than 100 years have passed, and there is still no reasonable explanation for this phenomenon, right? ”

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

Qiao Anhua said: "Professor Pang, what do you mean is that the so-called neutrino-free binary β decay does not produce neutrinos, but produces an inert neutrino that we cannot observe, so the so-called neutrino-free binary β decay phenomenon appears?" ”

Pang Xuelin nodded with a smile and said, "Let's start with the inscrutable neutrinos." We know that the Dirac equation is the field equation that describes fermions, and the positron is a hole with negative energy in the ocean of Dirac electrons. In 1937, the genius young physicist Majorana in Italy was dissatisfied with the asymmetry between electrons and positrons in the Dirac equation, and combined the fields of positive and antiparticle into a field that satisfies the symmetry of positive and antiparticle and Dirac equation at the same time. In his article, Majorana proposes that neutral neutrinos may be this new Majorana fermions. ”

In 1938, the promising Majorana mysteriously disappeared, and he has not been seen since. Whether neutrinos are Dirac fermions or Majorana fermions becomes a public question after that. In ordinary β decay, whether it is Dirac or Majorana's theory that electrons must be accompanied by antineutrinos, there is no difference in observation. In 1939, Fury of Harvard University proposed that the nature of neutrinos could be judged by looking for neutrino-free binary β decay, that is, looking for the binary β decay in which there are only two electrons and no neutrino end-state reaction. The principle of this reaction is that the nucleus of an atom with the number A and the charge number Z occurs at one time (A,Z)→ (A,Z+2)+e-+e-+v-e+v-e+v-e, because this reaction is required to occur at one time, it is necessary to ensure that the intermediate nucleus (A,Z+1) is an imaginary state, that is, its nuclear mass is required to be larger than that of the parent nucleus (A,Z), and the first β decay will not occur. The neutrino-free binary β decay requires the first β decay to release a virtual neutrino that is absorbed in the second β decay, so that a double beta terminal state without neutrinos is formed, and this reaction can only occur if the neutrino is a Majorana particle. There are more than 30 kinds of natural nuclei that meet such conditions. Interestingly, the early predicted neutrino-free β decay is more likely to occur than the ordinary β decay, with a half-life of around 1015. ”

"But now, I think we have a more reasonable explanation, in the β decay, the so-called first β decay, releasing a virtual neutrino to be absorbed in the second β decay, we might as well say that the first β decay produces an inert neutrino, in the second β decay this inert neutrino is transformed into another neutrino, and is absorbed by the second β decay, so there is no binary β terminal state of neutrinos. As for the experimental proof, I don't think it's too difficult, right?! ”

Qiao Anhua smiled: "It's not difficult, every doctoral student under me can do it!" ”

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

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