A Breakthrough Prize, again

For the second year in a row, a scientist at Maastricht University shares the Breakthrough Prize in Fundamental Physics. This time the prize is awarded to the Muon g-2 collaborations at CERN, Brookhaven National Laboratory, and Fermilab. At the Maastricht Science Programme, Gerco Onderwater is one of only a handful of Dutch scientists working in these collaborations. “I got involved with the experiments at Brookhaven National Laboratory shortly after obtaining my PhD in 1998 at the Vrije Universiteit and Nikhef”, he says about his work.

Muon

Across more than six decades, scientists and engineers have pushed experimental precision studying the muon, an elementary particle similar to the electron (the particle that powers your electronics), but it’s heavier and doesn’t last long. More specifically, they focus on a single, very significant number: the anomalous magnetic moment, basically, how strongly a muon acts like a tiny magnet.

This magnetic property of the muon tells us something about ‘empty’ space. Scientists believe that empty space isn’t actually empty. It is filled with a kind of invisible “foam” of particles that pop in and out of existence. By measuring how the muon’s magnetism is affected by this foam, physicists can check if there are hidden particles or forces that we don’t know about yet.

In short, the Muon g-2 collaborators test whether our current understanding of the universe (called the Standard Model) is complete or if there’s more to be discovered.

Analysis

Gerco coordinated the analysis of the experiment. “With a team of some 40 PhD students, postdocs, and staff from multiple laboratories in the USA, Europe, and Japan, we analysed the data with extreme precision (7 digits after the decimal point). In 2004 I was chosen to present the final Brookhaven result that showed a tantalising deviation from the prediction by the Standard Model. This shook up the world of particle physicists. Even the more precise follow-up experiment at the American Fermilab could not resolve this discrepancy.” 

Although the Muon g-2 experiments have ended, the tiny particle keeps fascinating Gerco. “We are designing a follow-up experiment at the Japanese J-PARC laboratory in which MSP students and I are involved.”