Matter-antimatter mixed atoms
Whenever scientists want to peer into the mysterious world of antimatter, they must borrow sophisticated technical means to prevent antimatter from coming into contact with the ordinary matter around it. This isolation is crucial because, as we all know, antimatter annihilates as soon as it comes into contact with ordinary matter.
But recently, an international team of researchers conducted an experiment at CERN that surprised many scientists by combining matter and antimatter into strange, stable hybrid helium atoms that behaved unexpectedly when immersed in superfluidic helium.
This new result may open up a new path for using antimatter to study the properties of condensed matter or to look for antimatter in cosmic rays.
Antimatter particles in a reducer
According to the Standard Model of particle physics, we know that particles and their corresponding antiparticles have exactly the same properties except for the charge that carries the opposite sign. Take, for example, a proton carrying a positive charge, whose antiparticle is an antiproton carrying a negative charge.
In past experiments, scientists have yet to find any evidence that there is any difference in the mass of protons and antiprotons, and if any such difference can be found, no matter how small, it will shake the foundations of physics.
Although all experimental evidence to date proves that their other properties are identical, scientists cannot rule out that this status quo is due to the lack of sensitivity of existing experimental methods to detect any nuances that may exist.
As a result, scientists around the world are still trying to improve various techniques to make more precise observations of the properties of antiparticles. The use of magnetic levitation to place antimatter atoms in a vacuum chamber for spectral measurements is a kind of observation hand break that scientists usually employ.
In the new study, the researchers used CERN's antiproton reducer to create exotic helium atoms containing antiprotons. In the antiproton reducer, the speed of antimatter particles produced by high-energy protons during the collision decreases, making it an ideal material for such experimental studies.
In the experiment, they mixed slow antiprotons with liquid helium cooled to near absolute zero, and a small number of antiprotons were trapped in the liquid helium, so that one of the two electrons that originally surrounded the helium nucleus was replaced by antiprotons, forming a structure that could remain stable for a long enough time to allow spectroscopic research to unfold.
In the new study, an electron in an atom is replaced by an antiproton to form a bizarre mixture of matter, the antimatter helium atom. | Image reference: Nature
Thin spectral lines at 2.2K
It was an exciting breakthrough. In fact, antimatter atoms in liquids have long been considered to be impossible to study with the high-resolution spectroscopy of lasers. Because in liquids, the strong interaction between densely arranged atoms or molecules can cause the spectral lines to be severely widened.
Immersing atoms in superflow helium widens the spectral lines. | Image reference: Nature
These spectral lines act like "fingerprints" used to identify each atom, they are the resonant images produced when atoms are excited by the energy absorbed from the laser beam. The exact position of the resonance line on the frequency scale and the shape of the line can reveal information such as the nature of the atom, the force acting on the antiparticle, and so on. If the resonance line is widened, this information is masked.
In the new study, the researchers looked at the spectra of antiproton helium atoms at different temperatures. They irradiated liquid helium with a laser emitted by a titanium sapphire laser that excites two resonances of antiproton atoms at two different frequencies, and the results showed that when the temperature drops below 2.2K, the shape of the spectral lines suddenly changes — and the wide spectral lines at higher temperatures become very narrow.
When one electron in a helium atom is replaced by an antiproton, the spectral lines narrow at a specific temperature. | Image reference: Nature
Below 2.2K, helium begins to enter a so-called superfluid state. Superfluids are a special state of liquid, one of the characteristics of which is the absence of internal friction. This is a typical quantum physics phenomenon that helium exhibits at extremely low temperatures.
At present, researchers do not know why antiproton spectral lines change so dramatically in such an environment, nor do they understand exactly what physical changes occur in the process.
Look for light in the darkness
Although there are still many unknowns, the researchers say the possibilities for this effect are far-reaching. The apparent narrowing of the resonance line makes it possible to distinguish so-called ultra-fine structures when atoms are excited by light. Ultrafine structures are the result of the interaction of electrons and antiprotons in atoms.
In addition to particle physics, this matter-antimatter helium atom can also be used in condensed matter physics and even in astrophysical experiments. Narrow, slender spectral lines help detect antiprotons and antideuterium nuclei in cosmic radiation. Using a superlubos helium detector may also help capture and analyze antiparticles from space, and may even help us solve another huge physics mystery – the nature of dark matter. The theory is that when dark matter interacts in the Galaxy's halo, antiprotons and antideuterium nuclei may be produced, which are then transported to Earth. So in a way, we can say that antimatter may be able to bring light to this "dark" mystery in the universe.
#创作团队:
Author: No. 2 Beidou
Typography: Wenwen
#参考来源:
https://www.mpq.mpg.de/6704191/03-superfluid-helium?c=2342
https://home.cern/news/news/physics/asacusa-sees-surprising-behaviour-hybrid-matter-antimatter-atoms-superfluid
#图片来源:
Cover image: LMU München/MCQST
Top image: LMU München/MCQST