Progress in research using positronium negative ions

An electron can be bound with its anti-particle, positron, to form positronium. Positronium can be considered to be the lightest “neutral atom” and is used in scattering experiments, antihydrogen synthesis, and solid surface studies. It has also been used to test quantum electrodynamics with high precision.

Another electron can also be bound to positronium to form a positronium negative ion. The formation of positronium negative ions was predicted theoretically in 1946 [1], and a large number of theoretical calculations have been performed since then. Positronium negative ions were actually produced in 1981, 35 years later [2]. Unfortunately, the production efficiency was low, and until 2008, only a few annihilation rate measurements were performed on positronium negative ions.

In 2008, it became possible to produce positronium negative ions with two orders of magnitude higher efficiency, and various studies have been conducted since then [3]. For example, it has become possible to produce an energy tunable positronium beam by generating positronium negative ions, accelerating them in an electric field, and then irradiating them with a laser beam to induce photodetachment [4].

The following studies have been performed recently:

(i) study of motion-induced resonance of positronium using the positronium beam [5] and

(ii) measurement of binding energy of the positronium negative ion [6].

These studies will be presented in the presentation.



[1] J. A. Wheeler, Ann. N. Y. Acad. Sci. 48, 219 (1946).

[2] A. P. Mills, Phys. Rev. Lett. 46, 717 (1981).

[3] Y. Nagashima, Phys. Rep. 545, 955 (2014).

[4] K. Michishio et al., Rev. Sci. Instrum. 90,023305 (2019).

[5] Y. Nagata et al., Phys. Rev. Lett. 124, 173202 (2020).

[6] K. Michishio et al., Phys. Rev. Lett. 125, 063001 (2020).