The collaboration of the ALPHA experiment at CERN, in which INFN National Institute for Nuclear Physics also participates, has succeeded in carrying out the most precise measurement ever made of a fundamental property of antihydrogen, the so-called hyperfine structure, improving its accuracy by around one hundred times. The result, which marks an important new step towards understanding antimatter, is reported in an article published today, 27 May 2026, in Nature.
According to the most widely accepted cosmological theories, matter and antimatter were produced in exactly equal quantities immediately after the Big Bang. However, the universe we know today is composed almost exclusively of matter: one of the major open questions in fundamental physics is therefore understanding what led to this imbalance.
“Studies on antimatter represent one of the most promising tools for addressing this cosmological enigma”, explains Simone Stracka, INFN researcher at the Pisa division. “If we were to observe even the slightest difference between matter and antimatter, we could obtain fundamental clues about the mechanisms that led to the predominance of matter in the universe”.
In this context, measuring the energy levels of antihydrogen, and comparing them with those of hydrogen, is of fundamental importance: it makes it possible to verify the validity of these symmetries and to explore possible deviations that could open the way to new physics. And one of the most sensitive observables is precisely the hyperfine structure of the ground state, linked to the interaction between the spins of the particles composing the atom. This parameter is known with extraordinary precision for hydrogen and has played a historic role in the development of quantum electrodynamics.
“The new result obtained by the ALPHA collaboration represents significant progress”, underlines Adriano Del Vincio, PhD student in the National PhD Programme in Space Science and Technology and INFN associate at the Pavia division. “The measurement of the antihydrogen hyperfine interval was carried out with an uncertainty of 4 parts per million (ppm), improving by around two orders of magnitude compared with previous determinations. At present, with the precision achieved, the result is compatible with that of hydrogen”.
The measurements were carried out using the ALPHA experimental apparatus, capable of producing, trapping and studying antihydrogen atoms. During the experiment, around 24,000 anti-atoms were analysed, produced by combining antiprotons and positrons and maintained in a magnetic trap at extremely low temperatures. The technique employed, based on microwave spectroscopy, made it possible to determine precisely the transitions between the energy levels of antihydrogen, from which the hyperfine interval is directly derived.
“This result represents a fundamental step in the study of antimatter. Thanks to the significant improvement in the precision of the measurement, we can compare the properties of matter and antimatter with ever greater sensitivity, testing the deepest principles of physics. It is an important achievement, made possible by the collective work of the ALPHA collaboration and by the development of increasingly advanced experimental techniques,” comments Germano Bonomi, researcher at the INFN Pavia division and professor at the University of Brescia.
This work opens the way to new precision studies on antimatter, with possible developments in understanding the differences between matter and antimatter and in testing quantum electrodynamics.
