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Matter–antimatter gas of positronium is laser cooled
01 Mar 2024
Researchers at CERN and the University of Tokyo have independently laser-cooled clouds of positronium. The breakthrough should make it easier to make precision measurements of the properties of antimatter and allow researchers to produce more antihydrogen.
Positronium is an atom-like bound state of an electron and its antiparticle the positron. As a hybrid of matter and antimatter, it is created in the lab to allow physicists to study properties of antimatter. Such studies could reveal physics beyond the Standard Model and could explain why there is much more matter than antimatter in the visible universe.
Positronium is currently created in “warm” clouds in which the atoms have a large distribution of velocities. This makes the precision spectroscopy difficult because an atom’s motion contributes to a slight Doppler shift in the light that it emits and absorbs. The result is a broadening of the spectral lines measured, making it difficult to see any tiny differences between spectra predicted by the Standard Model and experimental observations.
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New antimatter research
Managing to cool positronium to low temperatures could open up novel ways to study antimatter. Positronium is a good testbed for fundamental theories Hangst says, “There are two things that we should really understand in atomic physics, one is hydrogen and the other is positronium, because they only have two bodies.”
Precision spectroscopy can determine the energy levels of the positronium atom, and see whether they match with existing predictions made by QED. Similarly, the energy levels of positronium can be used to probe the effects of gravity on antimatter.
However, Christopher Baker, an ALPHA physicist from Swansea University, says that scientists still have a long way to go before precision spectral analysis can be done. “To get something useful, we need to come down to about 50 K,” he said. There are still things the team can do to bring down temperatures, such as cryogenically cooling the target converters or bringing in a second laser.
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