Particle physics: Antimatter measured with high precision

The most precise spectroscopic measurement of antimatter so far is reported in a paper published in Nature this week. The findings confirm the capabilities of anti-atom spectroscopy and bring the development of ultra-sensitive tests of antimatter one step closer.

A long-standing challenge for physicists has been to explain why matter, rather than antimatter, survived the Big Bang. It is thus of paramount importance to gain access to antimatter and understand its properties. In spectroscopy, the properties of atomic transitions are determined by exciting atoms with a laser and examining how they absorb or emit light. Although the same technique can be applied to study anti-atoms, antimatter is difficult to produce and trap, so its properties are difficult to measure.

In 2017, CERN’s ALPHA collaboration reported the experimental observation of the laser-driven 1S-2S transition - from the ground state to an excited state - in antihydrogen in a paper published in Nature. Now, Jeffrey Hangst and colleagues from the same collaboration present a detailed characterization of one of the hyperfine components of this transition. The authors studied about 15,000 atoms of antihydrogen, which they magnetically trapped in a cylindrical volume 280 mm long and with a diameter of 44 mm. Their measurements, conducted over a period of ten weeks, reveal that the resonance frequency for the considered transition in antihydrogen agrees with the expected frequency for the 1S-2S transition in hydrogen, with a precision of two parts in a trillion.