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Spectroscopy of Trapped Antihydrogen

Final Report Summary - HBAR12 (Spectroscopy of Trapped Antihydrogen)

Under the HBAR12 program, the CERN-based ALPHA collaboration, led by Professor Jeffrey Hangst of Aarhus University (DK) made the first-ever laser spectroscopic measurements on antihydrogen – the antimatter equivalent of the well-studied hydrogen atom. The underlying symmetries of the Standard Model of particle physics demand that hydrogen and antihydrogen have the same spectrum. ALPHA is the only experiment in the world to ever test this experimentally. The collaboration is able to produce, trap, and accumulate up to 1000 atoms of antihydrogen at a time – capabilities unique in the world. The collaboration first observed the 1S-2S transition in antihydrogen in 2016, and they succeeded in characterizing the shape of the spectral line in 2017. They find that antihydrogen is consistent with hydrogen at the level of 10-12 in frequency precision. This is the most precise direct measurement ever on antimatter. In the course of the program, ALPHA has also studied hyperfine interactions and the Lyman-alpha transition in antihydrogen. They have laid the groundwork for an active future of spectroscopic measurements on atomic antimatter – hopefully leading to hydrogen-like precision (10-15) in the near future.