iVEC Annual Symposium 2014 Anti-Hydrogen Formation by antiproton-positronium scattering Supervisor: Prof Igor Bray Institute of Theoretical Physics Charlie Rawlins, Curtin University of Technology Curtin University

iVEC Annual Symposium 2014 Positron-Hydrogen Scattering Required the use of the Convergent Close Coupling method (CCC) [1]. However the use of a positrons instead of electrons introduces some problems.

iVEC Annual Symposium 2014 Collision Processes for Positron- Hydrogen Scattering [2]

iVEC Annual Symposium 2014 Positronium [2] Positronium physically similar to a hydrogen atom, so it must be defined the same way. This is known as a two-centre CCC method since both Ps and H are defined using angular momentum and a Basis size [3,4]

iVEC Annual Symposium 2014 Anti-Hydrogen Formation Formation of positronium is the reverse of Hydrogen formation [5] Which is equivalent to Anti-Hydrogen formation [6, 7]

iVEC Annual Symposium 2014 Anti-Hydrogen Formation Why make Antihydrogen? If Antihydrogen formation can theoretically be produced with high probability, then people could attempt to make some for experimentation (i.e. gravitational behaviour of Antihydrogen). [8,9]

iVEC Annual Symposium 2014 Previous work Ground State Positronium (Ps(1s)) [10] 9,9 represents 9 atomic states and 9 positronium states The others represent using a large number of atomic states and only the Ps(1s) state. This symmetric and antisymmetric treatment

iVEC Annual Symposium 2014 Goal To see if higher cross-sections can be produced using the excited states of positronium, Ps(2p) and Ps(2s) [7]. This would require defining the H and Ps states in such a way that: The n=2 energy states are as expected The n=2 cross-sections produce smooth plots The n=1 cross-sections remain the same

iVEC Annual Symposium 2014 Approach Currently the program produces accurate data for Ps(1s). Increasing the size of the basis (N) should keep this accuracy of the Ps(1s) while increasing the accuracy of the Ps(2p) and Ps(2s) [4].

iVEC Annual Symposium 2014 Ps(1s) Results All follow a similar trend with increasing N. Small variations negligible Peak in region which is not experimentally feasible Minor k-grid manipulation required

iVEC Annual Symposium 2014 Ps(2s) and Ps(2p) Results Huge peaks eclipsing the other results Manipulation of k- grids does bring down the results but has not yet produced smooth results

iVEC Annual Symposium 2014 Problem Requires a lot more k-grid manipulation These states are at the threshold of reliability Not likely to be reliable A much larger N must be used

iVEC Annual Symposium 2014 Supervisor insight Increase basis size to N=20 Found that large cross-sections were produced for Ps(2p) and Ps(2s) scattering but for excited state hydrogen Hydrogen 2p would decay to Hydrogen 1s but Hydrogen 2s is metastable

iVEC Annual Symposium 2014 Acknowledgements Thank you iVEC for the funding and opportunity. Thank you Theoretical Physics Department for the workspace. Thank you Igor Bray for providing excellent supervision and assistance throughout this project.

iVEC Annual Symposium 2014 References 1.Bray,I. A, Stelbovics. (unknown). “Momentum-Space Convergant-Close-Coupling Method for Model e-H Scattering Problem” Computational Atomic Physics ed Barkshat K ((Heidelberg, New York):Springer) pp Bray, I. (unknown). electrons, positrons, photons or (anti)proton scattering from atoms, ions and molecules Kadyrov, A. S. and I. Bray (2002). "Two-center convergent close-coupling approach to positron-hydrogen collisions." Physical Review A 66(1): Kadyrov, A. S., et al. (2007). "Near-threshold positron-impact ionization of atomic hydrogen." Phys Rev Lett 98(26): Merrison, J. P., et al. (1997). "Hydrogen formation by proton impact on positronium." Phys. Rev. Lett. 78(14):

iVEC Annual Symposium 2014 References 6.Yamanaka, N. and Y. Kino (2004). "Antihydrogen formation in antiproton-positronium collisions." Nucl. Instrum. Methods Phys. Res., Sect. B 214: Charlton, M., et al. (1994). "Antihydrogen physics." Phys. Rep. 241(2): Charman, A. E., et al. (2013). "Description and first application of a new technique to measure the gravitational mass of antihydrogen." Nat Commun 4: Kellerbauer, A., et al. (2008). "Proposed antimatter gravity measurement with an antihydrogen beam." Nucl. Instrum. Methods Phys. Res., Sect. B 266(3): Kadyrov, A. S., et al. (2013). "Benchmark calculation of hydrogen (antihydrogen) formation at rest in positronium- proton (-antiproton) scattering." Phys. Rev. A: At., Mol., Opt. Phys. 87(6-A): / /