iVEC Annual Symposium 2014
Anti-Hydrogen Formation by
antiproton-positronium
scattering
Charlie Rawlins, Curtin
University of Technology
Supervisor: Prof Igor Bray
Institute of Theoretical Physics
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 PositronHydrogen 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]
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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
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Ps(2s) and Ps(2p) Results
• Huge peaks
eclipsing the other
results
• Manipulation of kgrids does bring
down the results but
has not yet
produced smooth
results
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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.
2.
3.
4.
5.
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 161-180
Bray, I. (unknown). electrons, positrons, photons or
(anti)proton scattering from atoms, ions and molecules.
http://atom.curtin.edu.au/igor/atomlab/index.html
Kadyrov, A. S. and I. Bray (2002). "Two-center convergent
close-coupling approach to positron-hydrogen collisions."
Physical Review A 66(1): 012710
Kadyrov, A. S., et al. (2007). "Near-threshold positron-impact
ionization of atomic hydrogen." Phys Rev Lett 98(26): 263202.
Merrison, J. P., et al. (1997). "Hydrogen formation by proton
impact on positronium." Phys. Rev. Lett. 78(14): 2728-2731..
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: 40-43.
7. Charlton, M., et al. (1994). "Antihydrogen physics." Phys. Rep.
241(2): 65-117.
8. Charman, A. E., et al. (2013). "Description and first application
of a new technique to measure the gravitational mass of
antihydrogen." Nat Commun 4: 1785..
9. Kellerbauer, A., et al. (2008). "Proposed antimatter gravity
measurement with an antihydrogen beam." Nucl. Instrum.
Methods Phys. Res., Sect. B 266(3): 351-356.
10. Kadyrov, A. S., et al. (2013). "Benchmark calculation of
hydrogen (antihydrogen) formation at rest in positroniumproton (-antiproton) scattering." Phys. Rev. A: At., Mol., Opt.
Phys. 87(6-A): 060701/060701-060701/060703.