Under this model, the basic particles in the whole universe are divided into four categories, namely quarks, leptons, vector bosons and scalar Higgs particles.
Among them, the vector boson is the mediator of interaction, which transfers the strong interaction, weak interaction and electromagnetic interaction between elementary particles through gauge interaction.
All elementary particles gain mass by interacting with Higgs particles. With the discovery of Higgs particle in 20 12 experiment, the standard model of particle physics completed the last piece of "puzzle", which proved the great success of the standard model.
However, there are still many problems in the universe that cannot be explained by the standard model, which shows that the standard model of particle physics is not the "ultimate" theory, but the "effective" theory under the standard of weak energy. There are new physics beyond the standard model that need to be explored urgently, which is also the main research content in the field of particle physics at present.
Dark matter research
Dark matter is beyond the standard model of particle physics and is a major problem to be solved urgently in physics and astronomy. Detecting dark matter in experiments and studying its physical properties will be a major breakthrough in physics.
There are three main directions for dark matter experimental detection-direct detection, indirect detection and collider detection.
The new generation of international dark matter direct detection experiment PandaX-4T 4t liquid xenon experiment was put into operation for the first time, which realized the strongest constraint on massive dark matter in the world.
Indirect detection, including dark matter particle detection (DAMPE) and AMS-02 space experiment, has accumulated more data and given more accurate measurements.
The search for dark matter on the LHC of the Large Hadron Collider at CERN is getting deeper and deeper into more complex parameter space, and preparing for the upcoming Run-3 phase.
China Jinping Underground Laboratory (CJPL) is the deepest laboratory in the world, which effectively shields the interference of cosmic rays and provides an extremely superior experimental environment. China has carried out PandaX liquid xenon experiment and CDEX high purity germanium experiment to directly detect dark matter.
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In recent 20 years, Italian DAMA/LIBRA experiments have claimed to observe the annual modulation signal produced by dark matter in NaI(Tl) crystal, but the corresponding dark matter signal parameters are excluded by various direct detection experiments.
In order to test this suspicious signal more accurately, international experiments have been tried with the same low background NaI(Tl) crystal.
In May, 20021,Canfrac underground laboratory in Spain announced the detection results of three-year exposure by using 1 12.5 kg ANAIS crystal detector, and no obvious annual modulation phenomenon was found. It is estimated that by the end of 2022, the experiment will have a sensitive exposure of more than 3 times the standard deviation, which can give more accurate conclusions.
Another cosine-100 experiment used 106 kg low background NaI(Tl) crystal, and no obvious annual modulation phenomenon was found in the exposure data of 1.7 a in Yang Yang underground laboratory, South Korea.
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In 2020, the XENON 1T liquid xenon experiment in Gran Sasso underground laboratory in Italy observed a suspected signal with a standard deviation of more than 3 times in the low-energy electron recoil data with an exposure of 0.65 t a, which aroused widespread concern in the field of dark matter theory and experimental research, and urgently needed further inspection by similar experiments.
The irradiation data of100t d were accumulated in the 580 kg liquid xenon experiment of PandaX-II in China. The characteristic spectra of the main radioactive impurities in xenon were obtained directly from the calibration data, and then the electron recoil data were analyzed according to these high-reliability background characteristic spectra.
The results of PandaX-II show that the suspected signals observed by XENON 1T are not contradictory to the current data, and it is necessary to improve the data statistics and detection sensitivity to give a definite conclusion.
The exclusion limits of the dark matter coupling constant (A) of the axion and the anomalous magnetic moment (B) of the neutrino in the PandaX-II experiment are not in contradiction with the suspected signal of Xenon1T.
Many types of dark matter detection experiments have been upgraded and developed internationally. Three experiments with liquid xenon as the target substance, PandaX-4T in China, XENONnT in Europe and LZ experiment in the United States, have increased the detection volume to several tons, and it is expected that the detection sensitivity will increase by more than 1 order of magnitude.
Among them, PandaX-4T liquid xenon experiment was installed and debugged at the end of 2020, becoming the first multi-ton liquid xenon detection experiment put into operation in the world, and the exposure reached 0.63 t a in the first half of 2002/KLOC-0.
PandaX-4T detector has applied a series of new technologies: a new generation of ultra-large and highly transparent time projection chamber detector has been developed, which greatly improves the uniformity of detector electric field and the amplification of electronic signals, and realizes high-resolution signal reconstruction; The trigger-free data reading method is adopted, which effectively reduces the detection threshold of weak signals; A new low-temperature xenon rectification system was developed, and 6 t xenon was successfully purified, and the content of radioactive impurity krypton 85 was reduced to 1/20 of PandaX-II. Effective use of liquid xenon self-shielding, combined with various radioactive measurement methods and surface cleaning technology, can reduce the radioactive background in the unit detection target to 1/20, and the radioactive impurity radon 222 content to 1/6.
The detection sensitivity of the first batch of data of PandaX-4T is 2.6 times that of PandaX-II, which gives the limit of the scattering cross section of the strongest massive dark matter in the world that has nothing to do with nuclear spin.
The first batch of data of PandaX-4T
Exclusion limit of spin-independent scattering cross section of dark matter
The yellow area is the "neutrino floor", that is, the detection sensitivity can detect the signal contribution of solar or atmospheric neutrinos in the detector.
These data also show that the PandaX-4T experiment began to touch the so-called "neutrino floor" near the dark matter mass of 10 GeV/ c 2, which means that it is possible to detect the coherent scattering signals of boron 8 neutrinos and xenon nuclei produced by solar nuclear fusion, which will be an important way to detect neutrinos in the future.
At the same time, the international community began to plan dozens of tons of "ultimate" liquid xenon detection experiments, one of which is to raise the sensitivity of dark matter detection to "neutrino floor". PandaX experimental team developed the corresponding key technologies.
Detectors with liquid argon as the target material also have unique detection sensitivity for massive dark matter, and the research and development of low background argon detectors with tens of tons is also continuing to advance.
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China CDEX experiment uses high purity germanium detector with point electrode, which can detect low energy threshold and has high sensitivity to light dark matter.
In 20021year, CDEX experiment announced the results of searching for effective dark matter signals by using 942.5 kg d exposure data.
In the direct detection experiment, the transfer momentum of the interaction between dark matter and target matter is small, so it can be systematically studied in the form of effective field operator, thus covering a variety of possible dark matter theoretical models.
In the analysis, CDEX experiment reduces the detection threshold to 160 eV. For small mass dark matter, the upper bound of coupling constants of various effective field models under non-relativity is systematically given.
At the same time, the exclusion limits of the strongest WIMP and π meson scattering cross sections in the world below 6 GeV/ c 2 mass are obtained by using chiral effective field theory.
At present, CDEX experiment is developing 50 kg high purity germanium detection array experiment, which is expected to improve the detection sensitivity by more than 2 orders of magnitude.
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For small mass dark matter, direct detection experiments also try different detection schemes to break through the detection threshold.
The liquid xenon detection experiment looks for low-quality dark matter through secondary effects such as independent ionization electron signal (S2 only), Migdal or bremsstrahlung.
For example, the analysis results of pure S2 data published in PandaX experiment at the beginning of 20021are used to find dark matter and electron scattering signals, and the strongest scattering cross section limit in the world is given in the mass range of dark matter 15~30 MeV/ c 2.
SENSEI experiment used about 2 g high impedance Skipper-CCD, and published the results of 24 d operation data at the end of 2020, giving the world's strongest restrictions on dark matter and electron scattering signals with mass of 0.5~ 10 MeV/ c 2, and dark photons with mass of 1.2~ 12.8 eV/ c 2.
SENSEI experiment is assembling and testing 100 g detection module, which will greatly improve the sensitivity of dark matter detection in this quality range.
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In the aspect of indirect detection of dark matter, China dark matter detection satellite DAMPE experiment and the International Space Station AMS-02 experiment continuously accumulate data.
202 1 published the physical data of AMS-02 experiment for 7 years, and gave more accurate measurement results of anti-electron and anti-proton.
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In the aspect of collider detection, ATLAS and CMS experiments on the LHC of the Large Hadron Collider continuously analyze all the data during the operation of Run-2, looking for the dark matter generation process and intermediate propagator signals.
Collider detection is not inhibited by the size of nuclear spin. By searching for the process of dark matter produced by quark or gluon annihilation, and directly searching for axis vector intermediate propagator by double injection of * * * vibration peaks, the results of direct detection experiment can be effectively supplemented.
Meanwhile, the collider experiment is looking for some dark matter models of complex processes. Among them, the dark Higgs model holds that the mass origin of dark matter may also have a breaking mechanism similar to Higgs-the dark Higgs may have a decay process similar to Higgs.
ATLAS experiment published the first search result of dark Higgs decaying into two vector bosons on 202 1, which limited the mass of intermediate propagator and dark Higgs.
The third phase of LHC is about to begin, and Run-3 will accumulate more data to further scan various dark matter generation models.
Study on neutrino and particle astrophysics
Particle astrophysics is closely related to particle physics research. Cosmic rays have high energy that man-made accelerators on earth can't reach, which provides us with valuable material samples for understanding the physical process of extremely high energy and looking for new physics.
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In 20021year, the most remarkable achievement in the field of particle astrophysics came from the high-altitude cosmic ray observatory, a major national science and technology infrastructure in China.
LHAASO was completed in 20021,passed the process acceptance smoothly, and officially entered the stage of scientific operation, carrying out the survey of gamma rays and cosmic rays with unprecedented sensitivity.
During the construction period, based on the 1/2 array data, the LHAASO cooperation group released the first batch of observation results: a large number of ultra-high energy cosmic accelerators were found in the Milky Way, and important progress was made in finding the origin of cosmic rays in Hanoi; Gamma-ray photons with energy of 1.4 PeV were recorded, which is the highest energy photon observed by human beings so far, creating a brand-new ultra-high energy gamma-ray astronomical window.
The Crab Nebula is one of the first ultra-high energy gamma ray sources discovered in 12, and has always been regarded as the "standard candlelight" in gamma ray astronomy. The latest achievement of LHAASO sets the brightness standard for this ultra-high energy band "standard candlelight".
LHAASO observed 0.88 PeV gamma-ray photons from the direction of the Crab Nebula.
These ultra-high energy γ -ray radiations produce electrons with energy band above PeV, which is close to the acceleration limit allowed by classical electrodynamics and ideal magnetohydrodynamics theory, and poses a severe challenge to the existing particle acceleration theory.
In the next few years, LHAASO will continue to carry out sky surveys in the northern sky area, scan gamma ray sources, and accurately measure the cosmic ray energy spectrum in the "knee" area, thus impacting the century mystery of the origin of cosmic rays.
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Another important material sample from the depths of the universe is high-energy neutrinos.
In 20021year, the ice cube neutrino observatory in Antarctic ice announced the first glashow * * * oscillation event-Glashow predicted that anti-electron neutrinos could interact with electrons to produce W bosons. The peak energy of neutrinos producing glashow oscillation is 6.3 PeV, which can be obtained from extreme celestial environment.
In this shower case, the energy of ice is 6.05±0.72 PeV. Considering the invisible energy in the cluster, the neutrino energy is revised to about 6.3 PeV；; . The secondary muon signal detected in the example shows the hadron decay process of the W boson, which provides further evidence for the glashow * * * vibration.
The glashow * * earthquake in ice cube once again verified the standard model of particle physics and revealed the existence of celestial anti-electron neutrinos.
The observation of glashow * * earthquake event is expected to limit the generation mechanism of celestial neutrinos.
The next few years will be a crucial moment for the development of neutrino astronomy. Many experimental groups at home and abroad put forward various plans for the next generation neutrino telescopes in ice, ocean and lake, and combined with the observation data of gamma rays, cosmic rays and gravitational waves, carried out multi-messenger astronomy research.
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In the process of searching for new physics beyond the standard three-flavor neutrino model, the MicroBooNE experiment of Fermi National Acceleration Laboratory in the United States released new measurement results, and no signs of inert neutrinos were found.
Previously, short baseline experiments such as LSND and MiniBooNE found that the number of neutrinos was abnormal, and a fourth neutrino, inert neutrinos, was introduced.
No inert neutrinos were found in the MicroBooNE experiment, indicating that the difference needs further study, and the abnormal number of neutrinos is still an unsolved mystery.
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In 20021year, the international neutrino-free double β decay experiment developed rapidly.
In large-scale experiments, CUORE and Kam? The LAND-ZEN experiment continues to collect data separately, and GERDA's succession experiment LEGEND-200 is about to start running.
In recent years, China's neutrino-free double β decay experiment has flourished, and many experimental groups have put forward many different experimental schemes, which once again illustrates the importance and significance of the neutrino problem in Mallorana.
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In 20021year, the construction of neutrino experiment in Jiangmen, China progressed smoothly, and data collection is expected to start in 2023. Accurate measurement of neutrino mass level and neutrino mixing parameters is expected to be the first to obtain internationally competitive experimental results.
Tomorrow, we will introduce the progress in three fields: the study of abnormal magnetic moment of daughter wood, the study of heavy taste and hadron physics, Higgs physics at the forefront of high energy, weak physics of electricity and the search for new physics, so please pay attention!
The full text of this paper was published inNo. 1 issue of Science and Technology Herald in 2022, with the original title of Summary of Hot Topics in Particle Physics in 20021year. This paper has been abridged. Welcome to subscribe.