Resonant scattering of positronium as a quasi-free electron in collisions with N2 and CO2

The present file contains the data supporting the findings of Shipman et al. (2017) [1].

Following the observation of the electronlike scattering of positronium (Ps) [2,3] using the positronium beamline at UCL [e.g. 3,5], the total cross sections for Ps + CO2, N2 collisions were measured and observed to display resonant structures in the vicinity of those in the corresponding electron data [4,1]. The measurements for both targets were analyzed by ascribing the energy shifts between the resonance positions for the two projectiles to the energy spent in distorting the Ps atom. The resulting reduced binding energy of Ps was then employed to estimate its Compton profile and used to convolute the electron data before comparing with the Ps measurements.

The quantitative consistency between the Ps data and the convoluted electron data explains the physical origin of Ps being resonantly scattered like a quasifree electron. Namely, the Ps atom is strongly polarized during the collision with the electron being on average closer to the target and the positron resonantly binding to the resulting temporary negative ion. The findings are in agreement with long-standing theoretical description of the nature of Ps resonances.

References

[1] M. Shipman, S.J. Brawley, L. Sarkadi,and G. Laricchia Phys. Rev. A 95, 032704 (2017). [2] S.J. Brawley, S. Armitage, J. Beale, D. Leslie, A. Williams, and G. Laricchia, Science 330, 789 (2010). [3] S.J. Brawley, S.E. Fayer, M. Shipman, and G. Laricchia, Phys. Rev. Lett. 115, 223201 (2015). [4] S.J. Brawley, A.I. Williams, M. Shipman, and G. Laricchia, Phys. Rev. Lett. 105, 263401 (2010). [5] M. Shipman, S. J. Brawley, L. Sarkadi, and G. Laricchia, Eur. Phys. J. D 68, 75 (2014).