ALPHA experiment takes antimatter to a new level

22 August 2018

ALPHA experiment

Jeffrey Hangst, spokesperson for the ALPHA experiment, next to the experiment.
(Credit: Maximilien Brice, Julien Ordan/CERN)

In a paper published in the journal Nature, the ALPHA collaboration at CERN, home of the Large Hadron Collider, reports that it has literally taken antimatter to a new level by observing the Lyman-alpha electronic transition in the antihydrogen atom, the antimatter counterpart of hydrogen, for the first time.

The finding demonstrates that ALPHA is quickly and steadily paving the way for precision experiments that could uncover as yet unseen differences between the behaviour of matter and antimatter.

The Lyman-alpha (or 1S-2P) transition is a special transition and in antimatter studies it could enable precision measurements of how antihydrogen responds to light and gravity. Finding any slight difference between the behaviour of antimatter and matter would rock the foundations of the Standard Model of particle physics and perhaps cast light on why the universe is made up almost entirely of matter, even though equal amounts of antimatter should have been produced in the Big Bang.

The ALPHA team makes antihydrogen atoms by taking antiprotons from CERN’s Antiproton Decelerator (AD) and binding them with positrons from a sodium-22 source. It then confines the resulting antihydrogen atoms in a magnetic trap, which prevents them from coming into contact with matter and annihilating. Laser light is then shone onto the trapped atoms to measure their spectral response. The measurement involves using a range of laser frequencies and counting the number of atoms that drop out of the trap as a result of interactions between the laser and the trapped atoms.

Professor Niels Madsen, from the Physics Department at Swansea University plays a leading role in the ALPHA experiment and said that “I think this result really demonstrates how ALPHA has succeeded in maturing the field of spectroscopy on antihydrogen.”

Professor Madsen is also one of the two UK Deputy Spokespeople for ALPHA, along with Dr Will Bertsche from the University of Manchester and added that “It’s amazingly satisfying to see how the pace of discovery has been accelerating in our experiment, from the first trapping in 2010, to now a second major result only a few months since the last one.This result is very promising and will likely pave the way for laser-cooling of antihydrogen that will allow even more precise measurements of all aspects of antihydrogen.” 

The UK has contributed to the ALPHA experiment through both physics and technical leadership with both Deputy Spokespersons coming from the UK, as well as positron accumulation and delivery, charged particle trapping, magnet design, experimental design and operation (EPSRC supported) and through the support of STFC for CERN membership.

You can read more about these results here.

More images here.

CERN website


The Science and Technology Facilities Council (STFC) co-ordinates and manages the UK’s involvement and subscription with CERN. The UK’s influence on both CERN Council and CERN Finance Committee is coordinated through the UK Committee on CERN (UKCC).

UK membership of CERN gives our physicists and engineers access to the experiments and allows UK industry to bid for contracts, UK nationals to compete for jobs and research positions at CERN, and UK schools and teachers to visit. UK scientists hold many key roles at CERN. Firms in the UK win contracts for work at CERN worth millions of pounds each year. The impact of winning contracts is often even greater as it enables companies to win business elsewhere.

Last updated: 23 August 2018

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