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Major Breakthrough in Antihydrogen Opens a New Door for Antimatter Studies

10 April 2018

Scientists have performed the most precise measurement of antimatter ever done. The ALPHA experiment was conducted at CERN and was led by Swansea University scientists. The experiment exposed the spectral structure of the antihydrogen atom, a huge breakthrough for antimatter research.

This is the ALPHA experiment. (Source: Maximilien Brice/CERN)This is the ALPHA experiment. (Source: Maximilien Brice/CERN)

The experimental results come after thirty years of research and development at CERN. The discovery of the antimatter's spectral structure opens the door for a new age of testing between matter and antimatter.

The hydrogen atom has its own spectral lines at specific wavelengths and relates to the emission of photons of a frequency or color when the electrons jump. CERN researchers have been attempting to find the antihydrogen match for these spectral lines.

The comparison of the measurements of antihydrogen atoms and hydrogen atoms tests the symmetry that is called charge-parity-time (CPT) invariance. Any difference, no matter how small, between the atoms would change the Standard Model of particle physics in a major way. It could also bring some kind of answer to a question that has plagued physicists for years: why is the universe made almost completely of matter, even though the Big Bang should have produced just as much antimatter?

Until now researchers could not produce and trap enough antihydrogen atoms to conduct these experiments. Creating the optical interrogation technology required for antihydrogen spectroscopy has also proven to be difficult.

To create antihydrogen, the ALPHA team bound antiprotons to positrons from a sodium-22 source and confined the antihydrogen atoms in a magnetic trap so they don’t touch matter. The team then shone laser light onto the trapped antihydrogen atoms and found that their response was relatable to the hydrogen response.

This approach was used in 2016 to measure the frequency of the electronic transition of antihydrogen between the lowest-energy state and the first excited state -- known as the 1S to 2S transition. The research team used two laser frequencies in this experiment and then counted the number of atoms that dropped from the magnetic trap.

"The precision achieved in the latest study is the ultimate accomplishment for us," explained Niels Madsen, deputy spokesperson for the ALPHA experiment and professor at Swansea University. "We have been trying to achieve this precision for 30 years and have finally done it."

For the most recent experiments, the researchers used detuned laser frequencies with slightly lower and higher frequencies. The team could measure the spectral shape and get a precise measurement of the central frequency of antihydrogen with this method. The antihydrogen shape matches the expected shape for hydrogen.

"This is real laser spectroscopy with antimatter, and the matter community will take notice," added Swansea University Professor, Michael Charlton. "We are realizing the whole promise of CERN's AD facility; it's a paradigm change.”

"This is a dream come true. Now we have our sight firmly set on improving the precision further to match experiments with ordinary hydrogen. This will be a formidable challenge but with the fantastic team we currently have I'm confident we will make progress" said Professor Stefan Eriksson, of Swansea University.

The paper on this research was published in the journal Nature.

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