Antihydrogen formation in collisions of positronium with antiprotons

Antihydrogen, consisting of a positron orbiting around an antiproton, is the simplest few body system consisting entirely of antimatter and as such is of considerable importance in providing additional tests of the validity of charge conjugation invariance. In addition, the nature of the gravitational interaction between matter and antimatter might more readily be investigated for an electrically neutral system than one which is charged. Before such studies can be undertaken the antihydrogen must, of course, be produced by attachment of a positron to an antipositron. Several production mechanisms have been proposed, the two most favored of which are radiative capture (spontaneous or stimulated) and charge exchange in positronium-antiproton collisions. The cross section for radiative capture is very much less than that for charge exchange, so that it might be thought that the latter process is greatly to be preferred. Various calculations of the cross section for the charge exchange process are briefly reviewed

Enhancement of antihydrogen formation in antiproton collisions with excited-state positronium

© Published under licence by IOP Publishing Ltd. Antihydrogen formation in positronium scattering on antiprotons is investigated using the two-centre convergent close-coupling method. A several orders of magnitude enhancement in the formation of antihydrogen is found when positronium is in an excited state. The effect is greatest at the lowest energies considered which encompass those achievable in experiment. This suggests a practical approach to creating neutral antimatter for testing its interaction with gravity and for spectroscopic measurements

Convergent variational calculation of positronium-hydrogen-atom scattering lengths

We present a convergent variational basis-set calculational scheme for elastic scattering of positronium atom by hydrogen atom in S wave. Highly correlated trial functions with appropriate symmetry are needed for achieving convergence. We report convergent results for scattering lengths in atomic units for both singlet ($=3.49\pm 0.20$) and triplet ($=2.46\pm 0.10$) states.Comment: 11 pages, 1 postscript figure, Accepted in J. Phys. B (Letter

Many-body theory of positron-atom interactions

A many-body theory approach is developed for the problem of positron-atom scattering and annihilation. Strong electron-positron correlations are included non-perturbatively through the calculation of the electron-positron vertex function. It corresponds to the sum of an infinite series of ladder diagrams, and describes the physical effect of virtual positronium formation. The vertex function is used to calculate the positron-atom correlation potential and nonlocal corrections to the electron-positron annihilation vertex. Numerically, we make use of B-spline basis sets, which ensures rapid convergence of the sums over intermediate states. We have also devised an extrapolation procedure that allows one to achieve convergence with respect to the number of intermediate-state orbital angular momenta included in the calculations. As a test, the present formalism is applied to positron scattering and annihilation on hydrogen, where it is exact. Our results agree with those of accurate variational calculations. We also examine in detail the properties of the large correlation corrections to the annihilation vertex.Comment: 25 pages, 16 figure

Cold neutral atoms via charge exchange from excited state positronium: a proposal

We present a method for generating cold neutral atoms via charge exchange reactions between trapped ions and Rydberg positronium. The high charge exchange reaction cross section leads to efficient neutralisation of the ions and since the positronium-ion mass ratio is small, the neutrals do not gain appreciable kinetic energy in the process. When the original ions are cold the reaction produces neutrals that can be trapped or further manipulated with electromagnetic fields. Because a wide range of species can be targeted we envisage that our scheme may enable experiments at low temperature that have been hitherto intractable due to a lack of cooling methods. We present an estimate for achievable temperatures, neutral number and density in an experiment where the neutrals are formed at a milli-Kelvin temperature from either directly or sympathetically cooled ions confined on an ion chip. The neutrals may then be confined by their magnetic moment in a co-located magnetic minimum well also formed on the chip. We discuss general experimental requirements

Induced long range dipole field enhanced antihydrogen formation in the pˉ+Ps(n=2)→e−+Hˉ(n≤2)\bar{p}+ Ps(n=2)\to e^- + \bar{H}(n\le 2) reaction

We assume all interaction to be Coulombic and solve the modified Faddeev equation for energies between the $Ps(n=2)$ and $\bar{H}(n=3)$, which involve six and eight open channels. We find that 99% of the antihydrogen are formed in $\bar{H}(n=2)$. Just above the $Ps(n=2)$ threshold the S, P, and D partial waves contribute more than 4000 square Bohr radii near the maximum. Evidences indicate that the induced long range dipole potential from the degenerate $Ps(n=2)$ targets is responsible for such a large antihydrogen formation cross section.Comment: 2 ps figure

Physics with antihydrogen

Performing measurements of the properties of antihydrogen, the bound state of an antiproton and a positron, and comparing the results with those for ordinary hydrogen, has long been seen as a route to test some of the fundamental principles of physics. There has been much experimental progress in this direction in recent years, and antihydrogen is now routinely created and trapped and a range of exciting measurements probing the foundations of modern physics are planned or underway. In this contribution we review the techniques developed to facilitate the capture and manipulation of positrons and antiprotons, along with procedures to bring them together to create antihydrogen. Once formed, the antihydrogen has been detected by its destruction via annihilation or field ionization, and aspects of the methodologies involved are summarized. Magnetic minimum neutral atom traps have been employed to allow some of the antihydrogen created to be held for considerable periods. We describe such devices, and their implementation, along with the cusp magnetic trap used to produce the first evidence for a low-energy beam of antihydrogen. The experiments performed to date on antihydrogen are discussed, including the first observation of a resonant quantum transition and the analyses that have yielded a limit on the electrical neutrality of the anti-atom and placed crude bounds on its gravitational behaviour. Our review concludes with an outlook, including the new ELENA extension to the antiproton decelerator facility at CERN, together with summaries of how we envisage the major threads of antihydrogen physics will progress in the coming years

A Catching Trap for All Antiproton Seasons

We describe the origin, development, and status of the Los Alamos antiproton catching trap. Originally designed for the antiproton gravity experiment, it now is clear that this device can be a source of low-energy antiprotons for a wide range of physics, both on site, at CERN, and also off site.Comment: 18 pages, LaTeX, 6 figures available upon request, In honor of Herbert Walthe