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Journal of Physics Conference Series

Collisions between anti-particles in presence of laser field

Chittaranjan Sinha, S. Ghosh Deb

Published Sep 1, 2009• 0 citations
Publisher

Abstract

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 ().

DOI
10.1088/1742-6596/185/1/012043

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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 ().
A quantum-mechanical approach is proposed for the formation of antihydrogen (H‾)(\overline{H})(H) in the ground and excited states (2s,2p)(2s,2p)(2s,2p) via the mechanism of three-body recombination (TBR) inside a trapped plasma of antiprotons (p‾)(\overline{p})(p​) and positrons (e+)({e}^{+})(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+{e}^{+}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 (H‾)(\overline{H})(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+{e}^{+}e+'s than for equal energies, as expected physically.
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.
Laser- assisted antihydrogen formation cross sections (differential and total) via the three - body recombination (TBR) process in a plasma of antiprotons and positrons are studied for the ground and excited states . Significantly large cross sections are obtained for low energies. The ground state antihydrogen cross section dominates throughout the energy range, essential for high precision spectroscopics studies in order to test the CPT theorem. The formation cross section are found to be much higher for unequal energies of the two positrons than for equal energies.
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.
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.
The formation of antihydrogen atoms from three-body collisions between positronium atoms and antiprotons plays a crucial role in the gravitational behavior of antihydrogen at rest (GBAR) experiment devoted to the measure of the action of gravity on antimatter. One of the main challenges facing this experiment is to find the means for increasing the production of antihydrogens which are produced by the reaction $\overline{p}+\text{Ps}\ensuremath{\rightarrow}\overline{\text{H}}+{e}^{\ensuremath{-}}$ with an extremely low rate. Along these lines, we investigate here the possibility to influence the collision process by using a laser field. A perturbative approach combining the Coulomb-Born approximation for modeling the charged-particle collision and a first-order perturbation theory for describing laser-atom interactions is employed to estimate laser-mediated charge-exchange cross sections. By carefully considering the laser specifications compatible with the experimental constraints, we present an extensive study of the influence of the laser parameters (laser wavelength and intensity) on the cross sections in the energy range of interest for GBAR. We show that under special irradiation conditions the rate of antihydrogen production may be significantly increased by the presence of the laser field.