Laser spectroscopy of the antiprotonic helium atom–molecule $${\bar pHe}^+$$

Abstract

The metastable antiprotonic helium atom–molecule (in short, atomcule), $${\bar pHe}^+$$ , which was discovered in 1991 as being the cause of the anomalous longevity of antiprotons with an overall lifetime of about 3 μs, now provides an exotic playground for laser spectroscopy, helped by the existence of numerous long lived states with 1–2 μs lifetimes. This three body system is characterized by a large angular momentum l ∼ 38 of $${\bar p}$$ coupled with the electron in the 1s ground orbital, and looks like an exotic hydrogen isotope with many different “nuclear states” as well as an exotic molecule with two centers (He2+ and $${\bar p}$$ ). So far, a number of laser resonance transitions have been identified. The present talk will cover the following topics: (1) high precision spectroscopy in comparison with three body theories involving the relativistic effect and QED, and (2) hyperfine structure of $${\bar pHe}^+$$ ;laser-microwave triple resonance.