The best measure of antimatter

Scientists from the ALPHA experiment at the European Particle Physics Laboratory (CERN) have taken the most accurate measurement of antimatter recorded to date. The advance has been achieved with about 15,000 atoms of antihydrogens magnetically trapped in a cylinder. One of the challenges physicists face is to explain why matter survived antimatter after the Big Bang, when it is supposed that they should have annihilated each other. Any advance to understand the properties of antimatter, like the one that has now been achieved in the European Laboratory of Particle Physics (CERN, near Geneva), is of the utmost importance to better understand this substance made up of antiparticles. By means of spectroscopic techniques, the international scientific collaboration ALPHA of CERN has recorded the most accurate measurement of antimatter. The study is published this week in the journal Nature.

In spectroscopy, the properties of atomic transitions are analyzed by exciting ‘normal’ atoms with a laser and then examining how they absorb or emit light. Although the same technique can be applied to the study of antiatomes, antimatter is much more difficult to produce and trap, so it is more complicated to determine its properties. In 2017, the collaboration ALPHA had already observed experimentally in antihydrogens the so-called transition 1S-2S, where these antimatter atoms (formed by an antiproton and an antielectron) passed from one fundamental state to another excited. Now what Jeffrey Hangst and his colleagues have achieved is to characterize in detail one of the hyperfine components of that transition.The authors studied about 15,000 antihydrogen atoms, magnetically trapped in a cylindrical volume of 280 mm long and with a diameter of 44 mm, for 10 weeks. The results revealed that the resonance frequency or maximum oscillation of the 1S-2S transition for the antihydrogen coincides with the expected frequency for this same transition in its homologue of matter, hydrogen, with an accuracy of two parts in a billion.

M. Ahmadi, Jeffrey Hangst et al. “Characterization of the 1S–2S transition in antihydrogen”. Nature, abril de 2018.

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