Speaker
Description
Although theoretical studies predict the existence of more than thirty positronium 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 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. Positronium compounds are formed via collisions between the positron beam and an effusive 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 within this experiment and compare them to the theoretical models available.
[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)