Europhysics Letters (EPL)

Multiphoton effects in three-body recombination for antihydrogen formation

S. Ghosh Deb, Chittaranjan Sinha

Published Oct 1, 2009• 1 citation

Abstract

Laser-assisted multiphoton cross-sections for the formation of antihydrogen ( ) via the three-body recombination (TBR) process in a plasma of antiprotons ( 's) and positrons ( e + 's) are studied for the ground and excited states (n=2 level). Significantly large enhancement is noted due to multiphoton effects particularly in the ground-state formation cross-section at lower incident energies with respect to the field-free case. The multiphoton ground-state cross-section dominates almost throughout the energy range (except at extreme low energies) in contrast to the field-free case. The formation cross-sections are found to be much higher for unequal energies of the two incident (active and spectator) e + 's than for equal energies.

DOI: 10.1209/0295-5075/88/23001

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Europhysics Letters (EPL)

Multiphoton effects in three-body recombination for antihydrogen formation

S. Ghosh Deb, Chittaranjan Sinha

Published Oct 1, 2009• 1 citation

Publisher

Abstract

DOI: 10.1209/0295-5075/88/23001

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Enhancement in Ground State Antihydrogen Formation via Three Body Recombination through Multiphoton effects

S. Ghosh Deb, Chittaranjan Sinha

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Physical Review AAug 1, 20069 citations

Recombination of antiprotons with positrons at low temperatures

Bernard Zygelman

Journal of Physics B Atomic Molecular and Optical PhysicsDec 20, 200211 citations

A quantum-mechanical approach is proposed for the formation of antihydrogen

(\overline{H})

in the ground and excited states

(2s,2p)

via the mechanism of three-body recombination (TBR) inside a trapped plasma of antiprotons

(\overline{p})

and positrons

({e}^{+})

or in the collision between the two beams of them. Variations of the differential as well as the total formation cross sections are studied as a function of the incident energies of both the active and the spectator

{e}^{+}

's. Significantly large cross sections are found at very low incident energies in the TBR process as compared to other processes leading to antihydrogen. The present

(\overline{H})

formation cross section decreases with increasing positron energy (temperature) but no simple power law could be predicted for it covering the entire energy range $(\ensuremath{\sim}5--50\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, corroborating the experimental findings qualitatively, the latter being at a much lower energy regime $(\ensuremath{\sim}{10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. The formation cross sections are found to be much higher for unequal energies of the two

{e}^{+}

's than for equal energies, as expected physically.

We study quantum mechanically the influence of an external laser field on the antihydrogen (

\overline{\mathrm{H}}

) formation cross sections in ground and excited states (2

s

p

) via the three-body recombination process inside a dense plasma of antiprotons and positrons, supposed to be the most efficient mechanism for cold and trapped antihydrogen. The plasma screening is considered in the framework of a Debye- H\"uckel potential. The laser polarization is chosen to be parallel to the incident momentum of the passive positron. The modifications due to the presence of the laser field are found to be quite significant both quantitatively and qualitatively for all the states. In the presence of a laser, the

\overline{\mathrm{H}}

formation cross sections are found to be suppressed significantly with respect to the field-free situation particularly in the ground state, while the excited state cross sections are in general enhanced at very low incident energies but are again suppressed at higher energies except for some special cases. The sensitivity of the formation cross sections with respect to the Debye length are also studied both in the laser-assisted and in the field-free situations. At very low incident energies, the ground state multiphoton formation is found to enhance with the increase in Debye screening, while the reverse is true for the excited states. These findings should have important implications for future

\overline{\mathrm{H}}

studies.

Laser-assisted antihydrogen

(\overline{\mathrm{H}})

formation cross sections (differential and total) for collisions of antiprotons with positronium (Ps) are studied in the framework of the eikonal approximation for two geometries, when the field polarization is parallel $({\ensuremath{\Vert}}^{L})$ or perpendicular $({\ensuremath{\perp}}^{r})$ to the incident Ps momentum. The variations of the

\overline{\mathrm{H}}

formation cross sections with respect to the field strength and the laser photon energy are studied for the multiphoton (absorption and emission) processes. The contribution of the atomic (both Ps and

\overline{\mathrm{H}}

) dressing terms to the enhancement of the

\overline{\mathrm{H}}

formation cross section is studied for both the geometries (${\ensuremath{\Vert}}^{L}$ and ${\ensuremath{\perp}}^{r}$). The most important prediction from the present work is the enhancement of the field-free (FF)

\overline{\mathrm{H}}

formation cross sections particularly at lower incident energies when the system

(\mathrm{Ps}+\overline{p})

is irradiated by a single mode, linearly polarized laser, the enhancement being more pronounced for a wider range of incident energy in the ${\ensuremath{\perp}}^{r}$ geometry than in the ${\ensuremath{\Vert}}^{L}$ one.