Cross Sections For Antihydrogen Formation Research Articles

Theoretical Study of Reactions in the $${{e}^{ - }}{{e}^{ + }}\bar {p}$$ Three Body System and Antihydrogen Formation Cross Sections

We apply a new highly efficient method of solving Faddeev-Merkuriev equations to multi-channel scattering calculations of the antihydrogen formation cross section for antiproton scattering off the ground and excited states of the positronium. Our results demonstrate good agreement with the known data on total and partial cross sections for all the reaction channels. Using moderate computational resources we have achieved a supreme energy resolution.

Comparison of classical and quantum models of anti-hydrogen formation through charge exchange

We compare classical and quantum predictions of the cross section for anti-hydrogen formation by charge exchange between Rydberg positronium and antiprotons as a function of the positronium energy. We show that these two highly different approaches furnish the same scaling law with the principal quantum number of positronium nPs and numerical values in agreement within some tens of percent for and down to very low collision energy of tens of μeV. We discuss these results in the context of a recently claimed hypothesis of quantum suppression of the reaction driven by supposedly different scaling law of classical and quantum predictions. Finally we underline how the basic agreement between classical and quantum results enforces the reliability of the classical calculations that, presently, are the only ones able to obtain the cross section for positronium initially in high Rydberg states and in the presence of external electric and magnetic fields.

Antihydrogen formation in low-energy antiproton collisions with excited-state positronium atoms

The convergent close-coupling method is used to obtain cross sections for antihydrogen formation in low-energy antiproton collisions with positronium (Ps) atoms in specified initial excited states with principal quantum numbers ni ≤ 5. The threshold behaviour as a function of the Ps kinetic energy, E, is consistent with the 1/E law expected from threshold theory for all initial states. We find that the increase in the cross sections is muted above ni = 3 and that here their scaling is roughly consistent with ${n_{i}^{2}}$ , rather than the classically expected increase as ${n_{i}^{4}}$ .

Near-threshold behavior of positronium-antiproton scattering

Using the convergent close-coupling theory we study the threshold behavior of cross sections for positronium (Ps) of energy $E$ scattering on antiprotons. In the case of $\mathrm{Ps}(1s$) elastic scattering, simple power laws are observed for all partial waves studied. The partial-wave summed cross section is nearly constant, and dominates the antihydrogen formation cross section at all considered energies, even though the latter is exothermic and behaves as $1/{E}^{1/2}$. For $\mathrm{Ps}(2s$), oscillations spanning orders of magnitude on top of the $1/E$ behavior are found in the elastic and quasielastic cross sections. The antihydrogen formation is influenced by dipole-supported resonances below the threshold of inelastic processes. Resonance energies form a geometric progression relative to the threshold. The exothermic antihydrogen formation cross sections behave as $1/E$ at low energies, but are oscillation free. We demonstrate that all these rich features are reproduced by the threshold theory developed by Gailitis [J. Phys. B: At. Mol. Phys. 15, 3423 (1982)].

Resonant antihydrogen formation in antiproton–positronium collisions

We study the influence of narrow resonances on antihydrogen formation cross sections via the three-body reaction . The latter is of interest for the gravitational behavior of antihydrogen at rest experiment that will be performed at CERN in the near future. The complex scaling method is employed to compute the positions and widths of these resonances, whereas the Kohn-variational principle is used for the determination of the scattering cross sections. A very good agreement is found with available theoretical results. The impact of these resonances on the cross section is analyzed.

An investigation of antiprotons collisions with positronium atom in Debye plasma environments

The effects of Debye plasmas on antihydrogen formation and ionization processes are investigated in antiprotons ( p¯) and positronium (Ps) collisions. The classical trajectory Monte Carlo method with Debye Huckel potentials has been used for cross section calculations. In this process, antihydrogen formation and ionization cross sections have been calculated in unscreened as well as in Debye plasmas conditions in energies ranging from 1 to 500 keV. Partial cross sections for antihydrogen formation are also calculated which show the largest cross sections correspond to production of antihydrogen in the n = 2 (2s, 2p) states. Comparative study has been carried out to determine the differences of cross sections in screening and unscreening cases. The results show that the cross sections for both antihydrogen formation and positronium ionization depend on Debye screening lengths as well as on collision energies. The effects of plasmas conditions on antihydrogen formation and positronium ionization are explain...

The Faddeev approach applied to antihydrogen formation

The differential cross sections for antihydrogen formation, in ground and excited states, from energetic antiproton–positronium collisions are computed analytically, using the Faddeev formalism in a second-order approximation. At the considered range of the impact energy, the second-order terms corresponding to the classical Thomas double-scattering processes are dominant. It is also shown that there exists a dynamical interference between two of the second-order partial amplitudes. Both amplitudes correspond to classical double-collision mechanisms in which the laboratory critical angle is 0.54 mrad. The interference between these amplitudes is approximately destructive for the capture into s-states with even parity.

Formation of antihydrogen in excited states

A two state approximation method used by author earlier for positron–hydrogen charge-exchange process is used to compute antihydrogen formation cross-sections in excited states. Cross-section results are compared with other existing calculations in the energy range 30 keV–500 keV. Total cross-section results for antihydrogen formation are also being reported.

Formation of antihydrogen in the ground state

Cross sections for antihydrogen formation in the ground state for the process [Formula: see text] + Ps(nlm) → [Formula: see text](1s) + e– have been calculated using charge conjugation and time reversal invariance. Calculations are based on a two-state approximation method, used by the author earlier for positron–hydrogen charge -exchange process (e+ – H → Ps(nlm) + p). Cross-section results are reported in the intermediate- and high-energy region (20 keV – 500 keV). PACS No.: 36.10.Dr

Comment on “Laser-assisted formation of antihydrogen”

In a recent paper, Whitehead, McCann, and Shimamura [Phys. Rev. A 64, 023401 (2001)] presented classical-trajectory Monte Carlo (CTMC) calculations of the effects of laser fields on the cross section for antihydrogen formation in collisions of antiprotons with positronium. They also use the same method to calculate the photoionization rate of isolated positronium in a strong field. The purpose of this Comment is to point out (i) the criteria for validity of the quasiclassical approximation are not satisfied for all the conditions used; (ii) some of their numerical results do not agree with the values obtained with a corroborated code; (iii) the ambiguity of a cross section when the target can ionize even before the projectile arrives; and (iv) the essential effect of quantum-mechanical tunneling on the strong-field ionization rate. A recently published method allowing tunneling in a CTMC calculation [J. S. Cohen, Phys. Rev. A 64, 043412 (2001)] is used for (iv). It is concluded that the laser effect on formation of antihydrogen may be much greater than that found by Whitehead et al., but the pulse must be better characterized for quantitative predictions.

Low-energy anti-hydrogen formation differential cross sections from Ps(n = 2) viathe modified Faddeev equations

Assuming CPT symmetry, we carried out calculations for the system p̄+Ps(n = 2)in the eight open channels energy gap between the Ps(n = 2) and H̄(n = 3)energy thresholds where we found anti-hydrogen formation cross sections as high as 1670πa02.We also report well converged anti-hydrogen formation differential cross sections from Ps(n = 2)targets using less than 10 partial waves. Very near the Ps(n = 2)threshold the differential cross sections are dominated by the first threepartial waves where most of the interference minimal structures seen inother energy regions are absent. Of particular interest are the large crosssection and the absence of interference minima in the differential crosssections when the target is in the metastable 2 3S1 state. The possibility ofutilizing these processes for low-energy anti-hydrogen synthesis is discussed.

Antihydrogen-formation cross sections in antiproton-positronium collisions with a time-dependent coupled-channel method

Antihydrogen-formation cross sections in antiproton-positronium collisions are calculated by using a time-dependent coupled-channel (TDCC) method. Nonuniform grid points are taken in the two-dimensional radial space to obtain accurate wave functions. High numerical accuracy of the TDCC method is demonstrated in a calculation of positronium-formation cross sections in positron-hydrogen collisions. The result is somewhat discrepant with previous results; in the present calculation, the cross section has a maximum of 16.19 in units of $\ensuremath{\pi}{a}_{0}^{2}=0.880\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16} {\mathrm{cm}}^{2}$ at an antiproton energy of 9.2 eV in the center-of-mass frame.

Antihydrogen formation in laser-assistedantiproton-positronium collision

We study the charge transfer between a positronium and anantiproton in the presence of a laser field. The interactions ofpositronium and antihydrogen with the laser field are treated to firstorder as time-dependent perturbations. The wavefunction of theejected electron is described by the Volkov state which makes thescattering matrix decompose into a series of sub-amplitudes formultiphoton processes. The cross section for antihydrogen formation,and its dependences on laser parameters (intensity, frequencyand polarization direction) are discussed.

Laser influence on positron-antiproton radiative capture collision

The laser-assisted radiative capture between a positron and an antiproton is studied in detail. The theoretical results show that the cross-section for antihydrogen formation is significantly reduced with the application of a laser background. This effect is most marked when the laser polarization is parallelto the incident direction.

Formation of antihydrogen by the charge-transfer reaction.

The cross sections for antihydrogen formation in the n=1, 2, 3, 4, 5, 6, and 7 levels from antiproton-positronium collisions are computed in the unitarized Born approximation (UBA). Twenty-seven physical states of antihydrogen (1s\ensuremath{\rightarrow}7h) and ten physical states (1s\ensuremath{\rightarrow}4f) of positronium are included in the UBA basis. The peak cross section for antihydrogen formation from excited positronium targets is much larger than that from a ground-state positronium target at low incident energies. The high-n antihydrogen levels make a significant contribution to the total antihydrogen formation cross section, especially for incident positronium atoms in the Ps(n=3) and Ps(n=4) levels.

Positronium and antihydrogen formation in the e+-H and Ps-p-bar systems.

The close coupling equations for the ${\mathit{e}}^{+}$-H and Ps-p\ifmmode\bar\else\textasciimacron\fi{} systems are solved for a model calculation comprising three hydrogen H(1s, 2s, 2p) and three positronium Ps(1s, 2s, Ps(1s), Ps(2s), and Ps(2p) states for ${\mathit{e}}^{+}$+H\ensuremath{\rightarrow}Ps+p reaction achieves a peak of 2.7\ensuremath{\pi}${\mathit{a}}_{0}^{2}$ and is smaller than the only existing set of experimental data. The cross section for antihydrogen formation in the Ps+p\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${\mathit{e}}^{+}$H\ifmmode\bar\else\textasciimacron\fi{} reaction reaches a maximum of (13--14)\ensuremath{\pi}${\mathit{a}}_{0}^{2}$ for incident antiproton energies between 6.5 and 11 keV.

Cross sections of antihydrogen formation in collisions of antiprotons with positronium

New calculations of the cross sections for antihydrogen formation in collisions of antiprotons with positronium are reported in the present paper. A multiple-scattering expansion method has been used for getting reliable results. Discussion and comparison of the present results are made with other theoretical calculations.

Formation of antihydrogen in p-bar-Ps collisions.

Cross sections for antihydrogen formation for the process p\ifmmode\bar\else\textasciimacron\fi{}+Ps\ensuremath{\rightarrow}H\ifmmode\bar\else\textasciimacron\fi{}+e have been calculated utilizing the charge-conjugation and time-reversal invariance as suggested by Humberston et al. [J. Phys. B 20, L25 (1987)]. Calculations are performed in the framework of the eikonal approximation for a wide range of antiproton energy (20--11 000 keV).

Theoretical cross sections for formation of antihydrogen in [formula omitted]+Ps collisions in the antiproton energy range 2–100 keV lab

We report semiclassical (impact-parameter) and classical cross sections for antihydrogen formation in collisions between antiprotons p and positronium atoms Ps computed in the intermediate energy range 2–100 keV lab for antiprotons.