Research, a new piece on antimatter revealed at CERN

It falls due to gravity like matter. The first direct observation of free-falling antihydrogen atoms confirms that it is subject to the same gravitational pull as matter

A new piece on antimatter has been revealed at Cern: it falls like matter because it is subject to the force of gravity. The discovery came from the scientific collaboration of the Alpha experiment at Cern, which also includes the National Institute of Nuclear Physics. The team of scientists from the Alpha collaboration managed to achieve, during the 2022 data collection, the first direct observation of the effects of gravity on the motion of antihydrogen atoms. The results are published in the journal Nature on September 28. This is the first measurement of gravitational interaction between matter and antimatter, in this case antihydrogen atoms, in the Earth’s gravitational field. The value obtained is compatible, within the experimental errors, with the predictions of general relativity.

Germano Bonomi, professor at the University of Brescia, associated with the Infn and member of the Alpha Collaboration explains that “although the gravitational interaction between matter and antimatter has been the subject of theoretical speculation since the discovery of the latter in 1928, it is the first time an experiment shows itself to be sensitive to the effects of gravity on antimatter atoms, particularly antihydrogen.” “It is a measure that the Antimatter Factory community at Cern – explains Bonomi – has been working on for almost two decades and as an Alpha collaboration we are therefore very happy to have finally succeeded”. In the experimental apparatus used for the measurement, called Alpha-g, the antihydrogen atoms, once created, are trapped, thanks to a magnetic field, in a vertical trap, between two coils which respectively determine the barriers of lower magnetic potential and superior.

The experimental strategy is based on balancing the gravitational force with the magnetic one and is conceptually simple: trap and accumulate antihydrogen atoms in the desired region, then slowly release them by lowering the upper and lower magnetic potentials of the vertical trap, and then try to measure any influence of gravity on their movement when they escape and annihilate on the walls of the apparatus. The effect of gravity manifests itself as a difference in the number of annihilation events from antiatoms escaping through the top or bottom of the trap.

“It was exciting to participate in this research, and in a laboratory like Cern where it is possible to find the best male and female scientists in the world” comments Marta Urioni, PhD student at the University of Brescia and member of the Alpha collaboration. “I was able to contribute both to the experimental phase of data collection and to that of the analysis for the extraction of the result which, within the experimental errors, is in line with what is expected from General Relativity” adds Urioni.

The scientists point out that since there are theoretical scenarios that predict an albeit very small violation of the gravitational acceleration between matter and antimatter, after determining the sign and approximate magnitude of the acceleration, the next few years will be dedicated to improving the experimental measurement .

“The level of precision is not yet such as to say something new about gravity compared to what we already know” explains Simone Stracka, researcher at the Infn in Pisa and member of the Alpha collaboration. “In the future – he observes – the challenge will be to verify the theoretical predictions with greater precision”. “In addition to our Alpha collaboration, other experiments at Cern, such as AEgIS and Gbar, are also carrying out this type of research and therefore we expect new progress soon” concludes Stracka.