UBC researchers help measure tiny energy gap in antimatter with improved precision

The ALPHA Collaboration improves its measurement of the ground-state hyperfine splitting of antihydrogen by two orders of magnitude.

Researchers at the ALPHA experiment—including University of British Columbia (UBC) and TRIUMF scientists—have achieved a hundredfold improvement in their measurement of a feature of the antimatter counterpart of the hydrogen atom.

The result, published in Nature, allows a precise comparison of hydrogen and antihydrogen, and is an important step in the effort to probe deeper into the nature of antimatter.

“This reflects nearly 20 years of Canadian leadership in antihydrogen microwave spectroscopy, a program initiated by Dr. Walter Hardy at UBC and Mike Hayden at Simon Fraser University,” says Dr. Makoto Fujiwara, senior research scientist at TRIUMF and spokesperson for the Canadian team in the international ALPHA project.

In the study, the ALPHA Collaboration measured the ground-state hyperfine splitting of the antihydrogen atom to extremely high precision. Antihydrogen comprises an antiproton orbited by a positron – the antimatter version of the electron. This is the tiny splitting of the atom’s lowest energy state due to the magnetic interaction between the antiproton and the positron.

The achievement allows stringent tests of quantum electrodynamics in antimatter – the best-working theory explaining the interactions between charged particles and light – to be carried out.

“This is an important milestone after nearly two decades of our work in antimatter spectroscopy,” says Dr. Takamasa Momose, a UBC chemical physicist and author on the paper.

“Looking ahead, we’re hopeful laser-cooling techniques for antihydrogen developed by our group can further improve the precision and open new opportunities for searching for possible differences between matter and antimatter that could help explain why our universe is made mostly of matter.”

Measuring the hyperfine splitting of antihydrogen is incredibly challenging, given that it annihilates as soon as it comes into contact with normal matter.

“The ground-state hyperfine splitting of hydrogen is the origin of the so-called 21-cm line, beloved by radio astronomers and researchers searching for extraterrestrial intelligence,” explains Jeffrey Hangst, spokesperson for the ALPHA experiment. “When the Antimatter Factory was conceived back in the 1990s, the hyperfine splitting of antihydrogen was one of the key targets for measurement that would justify constructing the facility.”

Since it began taking data in 2006, the ALPHA Collaboration has conducted more and more refined studies of the antihydrogen atom. And in 2017, they observed the ground-state hyperfine splitting of antihydrogen with a precision of 400 parts per million.

Now, thanks to several significant advances, including a novel technique that allows 15 000 antihydrogen atoms to be produced in a matter of hours, the ALPHA researchers have measured the hyperfine splitting of antihydrogen with a precision of 4 parts per million, an improvement of two orders of magnitude.

With files from the Alpha Consortium and TRIUMF.