Antihydrogen Relaxation from High-n to Ground State.

We explore the rate at which magnetized, high-n Rydberg pairs formed in antihydrogen experiments\footnote{G. Gabrielse, N.S. Bowden, P. Oxley, {\it et al.}, Phys. Rev. Lett. {\bf 89}, 213401 (2002); M. Amoretti, C. Amsler, G. Bonomi, {\it et al.}, Nature (London) {\bf 419}, 456 (2002).} relax to deep binding. While the theoretical three-body recombination rate scales favorably with low temperature ($\nu_{TBR} \propto nb^3 (n \bar{v} b^2 ) \propto T^{-9/2}$), pairs form with binding energies $\varepsilon$ near the (low) thermal level.\footnote{M.E. Glinsky and T.M. O'Neil, Phys. Fluids B {\bf 3}, 1279 (1991).}$^,$\footnote{R. Robicheaux and J.D. Hanson, Phys. Rev. A {\bf 69}, 010701 (2004).} Such atoms have classical drift orbits with negligible radiation. Collisions propel a cascade to deeper binding, but theory and simulation show an atom is unlikely to reach a radiating regime before it escapes the trap.\footnote{E.M. Bass and D.H.E. Dubin, Phys. Plasmas {\bf 11}, 1240 (2004).} However, simulations show that the energy-loss rate does not decrease as rapidly with increasing $\varepsilon$ as previously expected. We also discuss the mean magnetic moment of guiding-center atoms, and energy loss from adiation at deep binding, based on the classical Larmour formula and a presumption of stochastic orbits.