Using the classical trajectory Monte Carlo method, we calculated the charge-transfer cross section for antiprotons colliding with Rydberg positronium, leading to antihydrogen formation. The results show a significant influence of an externally applied magnetic field which causes a reduction of the cross section.
The antihydrogen formation by charge exchange between cold antiprotons and Rydberg positronium Ps∗ is studied by using the classical trajectory Monte Carlo method. In the absence of external magnetic field the cross section scaled by the fourth power of the Ps∗ principal quantum number nPs shows a universal behavior as a function of the ratio kv between the velocity of the Ps center of mass and that of the positron in the classical circular orbit. At low velocity, below about ${k}_{v}\ensuremath{\simeq}0.2--0.3$, we show for Rydberg positronium that the cross section increases as 1/kv2 or, in an equivalent way, as 1/EPscm with EPscm being the Ps∗ center-of-mass energy. In this regime the distribution of the principal quantum number of the antihydrogen state is narrow and it shows a peak at about 2nPs while at higher kv values a broad distribution of antihydrogen states is produced. The study of the collision process in the presence of moderate magnetic field (0.5--2 T) shows that there is an experimentally interesting region of kv with the cross section slightly higher than that in the absence of field. However the presence of a magnetic field changes significantly the cross section behavior as a function of kv, especially at low velocities, where reductions of the cross sections and deviations from the 1/kv2 (1/EPscm) are observed. Our calculations show a dependance of the cross section upon the angle between the magnetic field and the flight direction of the incoming Ps∗.
The aim of this work is to investigate the dynamics of collisions between ions and Rydberg atoms by using the Classical Trajectory Monte Carlo (CTMC) method. The study is started by collisions with oriented elliptical Rydberg atom, is then continued to collisions involving hydrogen Rydberg target in an external magnetic field in the l-mixing regime, and later arrives at antihydrogen formation in an external magnetic field where Rydberg positronium is taken as target.\nThe CTMC method has been applied in the study. For different targets, the CTMC method had to be adjusted and reconstructed to properly create the initial target state for the quasi-separable one-body initial system (hydrogen target) and the two-body initial system (positronium target). Charge exchange and ionization cross sections are calculated under special consideration of different initial target states.\nThe velocity matching phenomenon and Thomas capture which appears in the upstream-downstream asymmetry are found in ion-oriented elliptical Rydberg atom collisions, reflecting the important roles of the initial electron spatial and momentum distributions. By increasing the projectile charge, the distortion of the initial states caused by the strong perturbation of approaching projectile induces pronounced changes in the momentum distribution.\nIn the collisions involving hydrogen Rydberg atoms in a magnetic field, a cross section reduction in case of an increasing magnetic field is found for multiply charged projectiles. The structure effect due to the influence of the magnetic field on the initial state distribution results in different capture cross sections for two characterized, kmax and kmin, states. The velocity matching phenomenon as well as the effect of multiply charged projectile ion are observed in the collisions.\nFurthermore, antihydrogen formation in a magnetic field has been studied. Rydberg positroniums are assumed to be the target atoms, colliding with antiprotons. The initial target positronium state is carefully constructed by means of a newly introduced conserved operator, the pseudomomentum K. Similar properties as in the previous hydrogen target atom case were investigated. It is found that the existence of the magnetic field changes the spatial distribution of positronium to irregular motion. By increasing the magnetic field, it induces a decrease of the resulting capture cross sections (i.e. the antihydrogen formation). Thomas capture which happens in the collision plane in the field-free case is foiled. A smaller positronium binding energy and a larger geometrical extension of the target positronium atom yield a larger capture cross section.
We have performed calculations of two successive charge transfers from Rydberg states in a strong magnetic field. In the first charge transfer, a positron interacts with a highly excited atom to form positronium. In the second stage, the positronium interacts with an antiproton to give antihydrogen. For many parameters, our results are in qualitative agreement with previous calculations with no magnetic field. However, we do find that there are important changes which may affect the usefulness of the method for efficient formation of antihydrogen that can be trapped.
We have performed calculations of two successive charge transfers from Rydberg states in a strong magnetic field. In the first charge transfer, a positron interacts with a highly excited atom to form positronium. In the second stage, the positronium interacts with an antiproton to give antihydrogen. For many parameters, our results are in qualitative agreement with previous calculations with no magnetic field. However, we do find that there are important changes which may affect the usefulness of the method for efficient formation of antihydrogen that can be trapped.
The cross section for antihydrogen formation in collision of an antiproton with ground-state positronium has been calculated using the adiabatic hidden-crossing method. At collision velocities below the cross section maximum (3 keV) it is shown that the adiabatic approach provides a very simple description of the positron transfer process, in that capture occurs by a two-state mechanism involving coupling between the 1sσ and 2pσ potential curves only. Good numerical agreement with previous estimates is obtained. 1.
Antihydrogen formation involving magnetobound positronium is simulated by computing classical trajectories. Simulated collisions between electrons and positrons generate magnetobound positronium, which consists of electron–positron pairs that are not energetically bound but that have spatially correlated trajectories within a magnetic field. Simulations show that antihydrogen can form if such electron–positron pairs pass near antiprotons. In addition, the possibility of forming antihydrogen atomic ions or antihydrogen molecular ions via magnetobound positronium or magnetobound antihydrogen is discussed.