The search for the missing antimatter is heating up


CERN researchers have been able to measure the “electronic” transitions of antihydrogen with an accuracy 100 times greater than the last results of 2016. Their results have been published in the journal Nature.

The new results of the Alpha experiment, conducted by the European Nuclear Research Center (CERN), located in Switzerland, were eagerly awaited by the international community of physicists. It had to sift through antimatter atoms (in this case, antihydrogen) in search of tiny differences in their structure with respect to matter. The stake is considerable: it is a question of checking the theories which explain the current composition of the Universe, and in particular to explain the disappearance of antimatter.

Matter and antimatter have exactly — at least theoretically — the same mass and they are supposed to have been produced in equal quantities during the Big Bang. Also in theory, when matter and antimatter meet, they should annihilate each other. So the existence of matter in the Universe then remains a mystery. The hypothesis currently considered refers to a tiny difference in structure.

Still, to certify their theory scientists must manage to observe antimatter. This is where the CERN experiment, which had already delivered the first results in 2016, comes into play. The experiment consists of producing anti-hydrogen atoms and then studying them by laser spectroscopy.

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New results of unprecedented precision, covering some 15,000 of these antiatoms, have just been published in the journal Nature.

The challenge of CERN’s alpha experiment: to verify that a particular type of symmetry of the physical laws, regarding charge, parity and time (CPT symmetry), also applies to antihydrogen. Concretely, the researchers wanted to observe the “electronic” transition (here, positronic) of the state from lower to higher energy under the effect of a laser. The unique antielectron (positron) of the antihydrogen must pass from a low orbit to a high orbit (or vice versa) in a manner analogous to the electron of the hydrogen atom. To produce antihydrogen, CERN combined the antiprotons created by its antiproton decelerator with positrons from another dedicated machine.

The latest results achieve a more precise accuracy of a factor of 100 compared to those of 2016, even if we remain far from the accuracy achieved for hydrogen (of the order of 1/1015). And for now, antihydrogen behaves similarly to hydrogen. “So far, they are alike,” said Jeffrey Hangst of the Alpha experiment in a CERN statement.

New experiments will be necessary to detect a difference between matter and antimatter. But for researchers, these results are not disappointing. “Realizing laser spectroscopy on antimatter is already a paradigm shift,” says Jeffrey Hangst. A feat, perhaps, that will allow scientists to detect this famous difference between matter and antimatter one day.

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Shakes Gilles

Editor of The Talking Democrat. He enjoys bike riding, kayaking and playing soccer. On a slow weekend, you'll find him with a book by the lake.