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Nature: ALPHA-team takes antimatter to the next level

Professor at Aarhus University, Jeffrey Hangst, who leads the ALPHA collaboration at CERN in Geneva, has publishing groundbreaking results in Nature along with his research team. The results take our understanding of antimatter to the next level and contribute to our knowledge of the construction of the universe.

For the first time, researchers have observed the so-called Lyman-α electronic transition in the antihydrogen atom which is the antimatter counterpart to hydrogen. The energy spectrum of the electronic transitions in hydrogen has historically been crucial to the understanding of the structure of atoms and set the frame for the revolutionary atom-model of Niels Bohr, which earned him the Nobel Prize in 1922.

The ALPHA-collaboration, being the only ones who can trap and measure antihydrogen at this point in time, will pave the way for precision experiments with their new results which could expose yet unseen differences between the behavior of matter and antimatter.

“We are really excited about this result. he Lyman-alpha transition is notoriously difficult to probe – even in ‘normal’ hydrogen. But by exploiting our ability to trap and hold large numbers of antihydrogen atoms for several hours and using a pulsed source of Lyman-alpha laser light, we were able to observe this transition. Next up is laser cooling, which will be a game-changer for precision spectroscopy and gravitational measurements,” says Professor Jeffrey Hangst, who has been supported financially by the Carlsberg Foundation for years.

The Carlsberg Foundation chairman, Flemming Besenbacher, says:

“As a leader of the ALPHA collaboration at Cern, Jeffrey Hangst has managed to expand our knowledge on anti-matter, once more. It is impressive, that we are now able to measure the Lyman-α-transition in anti-hydrogen with a precision of a few parts in a hundred million. The research of Jeffrey Hangst is outstanding by international standards, and his latest result deserves congratulations.”

The physics behind the measurements

The Lyman-α-transition is one of several in the Lyman-series of electronic transitions that were discovered in atomic hydrogen just over a hundred years ago by physicist Theodore Lyman. The transition occurs when an electron jumps from the lowest energy level (1S9 to a higher energy level (2P) to fall back to the 1S-level by emitting a photon at the wavelength of 121,6 nanometres.

The ALPHA research team makes antihydrogen atoms by taking antiprotons from CERN’s Antiproton Decelerator (AD) and binding them with positrons from a sodium-22 source. Next, they confine the antihydrogen atoms in a magnetic trap, which prevents them from coming into contact with matter, which would cause their annihilation. Laser light is shone onto the trapped atoms to measure their spectral response. The measurement involves using a series of laser frequencies and counting the number of atoms to fall out of the trap due to the interactions between the laser light and the trapped atoms.

The ALPHA collaboration has previously used this technique to measure the so-called 1S-2S transition. By using the same approach and a number of laser wavelengths around 121,6 nanometres, ALPHA has now measured the Lyman-alpha transition in antihydrogen with a precision of a few parts in a hundred million, which is in good agreement with the corresponding transition in hydrogen.

Read the article in Nature

This article is based on a press release from Cern written by Ana Lopes

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