We report on the anisotropic photodetachment of positronium negative ions, followed by the dissociation into $p$-wave electrons and positronium atoms, with a linearly polarized laser beam. We have observed a strong recoil effect of the photoelectrons on the translation momentum of the dissociated positronium atoms. With polarization angle-resolved measurements, the asymmetry parameter of the photoemission angular distribution of the ions at a photon energy of 1.165 eV was determined to be $1.97\pm 0.04(\mathrm{stat})\pm 0.07(\mathrm{syst})$, in agreement with a theoretical prediction. The present method can be applied to explore the unrevealed dissociation dynamics of exotic particle systems and their manipulation with polarized light.

• Received 14 January 2024
• Revised 25 March 2024
• Accepted 18 April 2024

DOI:https://doi.org/10.1103/PhysRevLett.132.203001

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Published by the American Physical Society