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Laser-stimulated radiative recombination of antihydrogen in a magnetic field in the presence of Doppler broadening

Vladislav Viktorovich Serov, Vladimir Leonardovich Derbov, V. I. Lobanov, Ochbadrakh Chuluunbaatar, Alexander A. Gusev, Sergue Il'ich Vinitsky

Published Jun 13, 2007• 0 citations
Publisher

Abstract

To enhance the laser-stimulated recombination of antihydrogen from cold antiproton-positron plasma in a trap we propose to use a new resonance mechanism involving the quasi-stationary states of the positron that arise from the joint action of the Coulomb field of the antiproton and the strong magnetic field of the trap. The recombination rate is expressed via the cross-section of laser ionization of the atom that has strongly non-monotonic frequency dependence due to the presence of quasi-stationary states merged into the continuum background. The estimates using previously calculated ionization cross-section show the possibility to enhance the laser-stimulated recombination by means of the optimal laser frequency choice.

DOI
10.1117/12.754462

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To enhance the laser-stimulated recombination of antihydrogen from cold antiproton-positron plasma in a trap we propose to use a new resonance mechanism involving the quasi-stationary states of the positron that arise from the joint action of the Coulomb field of the antiproton and the strong magnetic field of the trap. The recombination rate is expressed via the cross-section of laser ionization of the atom that has strongly non-monotonic frequency dependence due to the presence of quasi-stationary states merged into the continuum background. The estimates using previously calculated ionization cross-section show the possibility to enhance the laser-stimulated recombination by means of the optimal laser frequency choice.
To increase the efficiency of laser-induced recombination of antihydrogen from cold antihydrogen—positron plasma in a trap, it is proposed to use a new resonance mechanism with the participation of positron quasi-stationary states, arising under the joint action of an antiproton Coulomb field and a strong magnetic field of the trap. The recombination rate is expressed through the atomic laser ionization cross section whose frequency dependence is nonmonotonic due to the presence of quasi-stationary states against the background of the continuum. The estimates with the use of the ionization cross sections calculated earlier demonstrate the possibility of improving the efficiency of the laser-induced recombination at an optimally selected laser frequency.
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 ().
Summary form only given. In the present report we propose a combination of pulsed electric field and laser pulse field at wavelength near 800 nm to stimulate the formation of antihydrogen atoms in lower states (n = 3) in positron-antiproton plasma under the conditions of Penning and Paul traps at low temperatures. The laser intensity estimated is about dozens of W/cm/sup 2/. In crossed constant magnetic field and circularly polarized alternating electric fields a new kind of stationary rotating wave packet states were shown to arise in hydrogen-like systems under special conditions. These packets, knows as Trojan states, remain strongly localized and thus differ significantly from common Rydberg states. Using numerical modeling of wave packet dynamics we analyse the stability of these states with respect to field perturbations and estimate the possibility to use them as intermediate states for antihydrogen production. We discuss the polarization dependencies of the laser-induced recombination rate for the case of the anisotropic velocity distribution.
We propose a new mechanism that can contribute to the spontaneous recombination of antihydrogen atoms in traps containing cold positron-antiproton plasma in the presence of a constant magnetic field. The latter plays a principal role restricting the motion of the positron in the transverse plane and, finally, prolonging the time during which the positron can lose its energy due to spontaneous radiation. Classical and quantum mechanical estimates are presented under the conditions close to those experimentally realized in the existing traps.
We study quantum mechanically the influence of an external laser field on the antihydrogen (H‾\overline{\mathrm{H}}H) formation cross sections in ground and excited states (2sss,2ppp) 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 H‾\overline{\mathrm{H}}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 H‾\overline{\mathrm{H}}H studies.
Antihydrogen, the bound state of an antiproton and a positron, is of interest for use in precision tests of nature's fundamental symmetries. Antihydrogen formed by carefully merging cold plasmas of positrons and antiprotons has recently been trapped in magnetic traps. The efficiency of trapping is strongly dependent on the temperature of the nascent antihydrogen, which, to be trapped, must have a kinetic energy less than the trap depth of . In the conditions in the ALPHA experiment, the antihydrogen temperature seems dominated by the temperature of the positron plasma used for the synthesis. Cold positrons are therefore of paramount interest in that experiment. In this paper, we propose an alternative route to make ultra-cold positrons for enhanced antihydrogen trapping. We investigate theoretically how to extend previously successful sympathetic cooling of positrons by laser-cooled positive ions to be used for antihydrogen trapping. Using simulations, we investigate the effectiveness of such cooling in conditions similar to those in ALPHA, and discuss how the formation process and the nascent antihydrogen may be influenced by the presence of positive ions. We argue that this technique is a viable alternative to methods such as evaporative and adiabatic cooling, and may overcome limitations faced by these. Ultra-cold positrons, once available, may also be of interest for a range of other applications.