Speaker
Description
Positronium (Ps), the short-lived bound state of an electron and its antimatter counterpart the positron, can form a variety of exotic molecular systems. Although theoretical studies predict the existence of more than thirty Ps compounds [1], experimental observation remains limited to the simplest systems, positronium hydride (PsH) [2] and deuteride (PsD) [3]. Ps compounds are relevant in multiple fields, including many-body quantum calculations [1], materials studies [3], and antihydrogen ion formation [4], but the lack of experimental results means calculations are unvalidated. We report a renewed experimental effort to search for and characterise these molecules, such as PsH, PsO and PsF, by measuring their binding energy with a precision of approximately 50 meV.
To this end, we have constructed a dedicated positron beamline based on a $^{22}$Na source, a Surko-type buffer-gas positron trap, and a 1 amu resolution time-of-flight mass spectrometer. The trap produces positron bunches characterised by a narrow energy spread of 59 ± 1 meV. Ps compounds are formed via collisions between the positron beam and an effusive molecular gas-jet target e$^+$ + AB → A$^+$ + PsB, employing a methodology analogous to that used in Ref. [2]. The ion produced in the collision is identified in a time-of-flight mass spectrometer using a microchannel plate detector (MCP), its appearance below the threshold for Ps production indicating if the Ps compound is made.
We present the first measurements of this experiment and compare them to the available theoretical models.
[1] X. Cheng et al., Phys. Rev. A 85, 012503 (2012).
[2] D. M. Schrader et al., Phys. Rev. Lett. 69, 57 (1992).
[3] M. A. Monge et al, J. Radioanalytical and Nuclear Chem. 211, 23-29 (1996).
[4] J. Taylor et al., Phys. Rev. A 109, 052816 (2025).