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Journal of Physics B Atomic Molecular and Optical Physics

Three-body recombination with mixed sign light particles

F. Robicheaux

Published Jan 3, 2007• 7 citations
Publisher

Abstract

Using a classical trajectory Monte Carlo method, we have computed the three-body recombination (two free positrons and an anti-proton scattering into one free positron and an anti-hydrogen atom: e+ + e+ + p ̄ → ¯H + e+) in the presence of electrons. By simply reversing the sign of all of the particles, these results can be applied to three-body recombination of matter in the presence of positrons. An important parameter is the fraction of light particles which are of the opposite sign; we performed calculations for several values of this parameter and find a substantial effect even for small fractions. We have also included a strong magnetic field in the calculation since this seems the most likely way to have mixed sign light particles in the same region of space. Our results will be useful for future anti-hydrogen experiments. We identify the main mechanisms controlling the recombination process. 1.

DOI
10.1088/0953-4075/40/2/003

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Using a classical trajectory Monte Carlo method, we have computed the three-body recombination (two free positrons and an anti-proton scattering into one free positron and an anti-hydrogen atom: e+ + e+ + p ̄ → ¯H + e+) in the presence of electrons. By simply reversing the sign of all of the particles, these results can be applied to three-body recombination of matter in the presence of positrons. An important parameter is the fraction of light particles which are of the opposite sign; we performed calculations for several values of this parameter and find a substantial effect even for small fractions. We have also included a strong magnetic field in the calculation since this seems the most likely way to have mixed sign light particles in the same region of space. Our results will be useful for future anti-hydrogen experiments. We identify the main mechanisms controlling the recombination process. 1.
Using a classical Monte Carlo method, we have computed the three-body recombination (two free electrons and a proton scattering into one free electron and a hydrogen atom: $e+e+\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{H}+e)$ in strong magnetic fields. The proton is allowed its full motion whereas the motion of the electron is given by the guiding center approximation. We investigate recombination for temperatures and fields similar to those used in recent experiments that generated anti-hydrogen. When the proton has the same temperature as the electrons, the recombination rate for the more elaborate equations of motion is roughly 60% larger than for the $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\infty}$ approximation. The recombination rate decreases as the proton speed approaches the electron thermal speed; the variation of this rate has implications for the directionality of the anti-atoms formed in recent experiments. We report on several properties of the atoms formed by three-body recombination in strong magnetic fields.
Using a classical Monte Carlo method, we have computed the three-body recombination (two free electrons and a proton scattering into one free electron and a hydrogen atom, $e+e+p\ensuremath{\rightarrow}\mathrm{H}+e$) in strong magnetic fields. The proton is fixed in space but the electrons are allowed their full, three-dimensional motion. We investigate recombination for temperatures and fields similar to those used in recent experiments that generated antihydrogen. The present rate is compared to that when the electrons' motion is given by the guiding center approximation, validating previous results at low temperature and demonstrating the breakdown of this approximation at higher temperature. Unlike the B=0B=0B=0 case, strong BBB gives preferential recombination to atoms with positive magnetic moment. Also, the canonical angular momentum in the field direction is often negative even when the magnetic moment is negative. Both results affect the trapping of antihydrogen using spatially dependent magnetic fields.
Using a classical Monte Carlo method, we have computed the three-body recombination (two free electrons and a proton scattering into one free electron and a hydrogen atom, $e+e+p\ensuremath{\rightarrow}\mathrm{H}+e$) in strong magnetic fields. The proton is fixed in space but the electrons are allowed their full, three-dimensional motion. We investigate recombination for temperatures and fields similar to those used in recent experiments that generated antihydrogen. The present rate is compared to that when the electrons' motion is given by the guiding center approximation, validating previous results at low temperature and demonstrating the breakdown of this approximation at higher temperature. Unlike the B=0B=0B=0 case, strong BBB gives preferential recombination to atoms with positive magnetic moment. Also, the canonical angular momentum in the field direction is often negative even when the magnetic moment is negative. Both results affect the trapping of antihydrogen using spatially dependent magnetic fields.
Antihydrogen is at the focus of antimatter research.One of the main aims is to perform a direct test of the fundamental CPT symmetry by comparing the spectroscopic properties of the ground-state antihydrogen atom with those of the hydrogen atom.In current experiments synthetized antihydrogen is formed mainly via the three-body recombination process after mixing positron and antiproton clouds together in a cryogenic trap.The major three-body formation process populates mainly highly excited Rydberg states, therefore before the antihydrogen atoms reach the ground-state additional processes may take place, such as collisional (de)excitation, ionization and spontaneous or stimulated radiative transitions.We have used a classical-trajectory Monte Carlo (CTMC) code along with regular atomic codes to generate a scattering database of rate coefficients in various experimentally achievable magnetic field strengths and in low temperature positron plasma conditions.We used these rates to calculate the evolution of level population of antihydrogen during formation, scattering and flight within our experimental conditions [1].The model and the results are presented.
In the present paper two-body radiative recombination rate for the production of antihydrogen Π) in a merged beam of slow positrons (e+) and antiprotons (p -) is studied in the light of a two-step process, which consists of capture in an excited state of II with subsequent decay to the ground state and emission of a photon.Computation is done using the field theory and the Coulomb gauge.Importance of the two-step radiative recombination process relative to the well-known spontaneous photorecombination process, on the two-body radiative recombination rate for antihydrogen formation, is discussed.The present result predicts higher contribution from the two-step radiative recombination process as compared to the spontaneous photorecombination process to the rate of cold antihydrogen formation witl the relative colfision energy below 0.01 Rydberg, near which experiments are being conducted.However, above 0.1 Rydberg the spontaneous photorecombination process dominates over the two-step radiative recombination process.The present result is valid, as well, for the formation of hydrogen atom due to collision between slow edectron and proton.
Three body recombination (TBR) process for the formation of antihydrogen () inside a trapped plasma of antiprotons () and positrons (e+), supposed to be the most efficient mechanism for the production of cold and trapped antihydrogen is studied quantum mechanically. Present study also involves a background laser field anticipating further enhancement of the formation cross sections. Significantly large cross sections are obtained in the presence of the field at lower incident energies as compared to the field free ones. Cross sections are enhanced for higher excited states of ().