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Gomer, V.; Harms, Oliver; Haubrich, D.; Schadwinkel, H.; Strauch, F.; Ueberholz, B.; Wiesche, Stefan aus der; Meschede, Dieter

doi:10.1023/a:1012621904575

Cited by 14 publications

(6 citation statements)

References 17 publications

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“…These atoms are moving with a speed close to that of light. Their future plan is to obtain H at thermal velocities and to trap H. Impressive progresses have been made in this direction [3][4][5].Availability of H at sub-milli-Kelvin energies will make it possible to compare directly matter and anti-matter properties with high precision [6][7][8]. It has been pointed out that the main cause of loss of H trapped in a magnetic gradient trap is due to H-H 2 and H-He collision processes.…”

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confidence: 99%

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Hydrogen–anti-hydrogen elastic scattering using fully quantal method

Sinha¹,

Ghosh

2000

Europhys. Lett.

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Hydrogen-anti-hydrogen scattering has been studied at low energies using quantal method. We employ the close-coupling method using different atomic basis sets. The same method has also been used to investigate hydrogen-hydrogen scattering. s-wave phase shifts and integrated elastic cross-sections are reported for both the systems. There is a structure in the elastic cross-section for hydrogen-hydrogen scattering.European physicists were successful in preparing anti-hydrogen (H) at CERN [1] by using a low-energy anti-proton (p) ring in late December 1995, and more recently at Fermilab [2]. These atoms are moving with a speed close to that of light. Their future plan is to obtain H at thermal velocities and to trap H. Impressive progresses have been made in this direction [3][4][5].Availability of H at sub-milli-Kelvin energies will make it possible to compare directly matter and anti-matter properties with high precision [6][7][8]. It has been pointed out that the main cause of loss of H trapped in a magnetic gradient trap is due to H-H 2 and H-He collision processes. The scattering cross-sections for these processes will help to fabricate a technical know-how in slowing down and trapping H. Therefore, theoretical investigations of these processes are of great importance.To the best of our knowledge, no positive-energy calculation has so far been carried out for matter-anti-matter systems with anti-matter signature. On the other hand, different workers have studied atom-atom scattering. Bates and Griffing [9] have initiated the study on the H-H system using the first Born approximation. Shingal et al. [10] have investigated H-H scattering using a coupled-channel semi-classical impact parameter method with rectilinear trajectories and reported the excitation and ionization cross-sections in the energy range 1 to 100 keV. They have used a 22-state basis for each state of symmetry. The semi-classical impact parameter method is not expected to be valid at low energies. In heavy-particle collision a large number of partial waves unlike light particle scattering are required for convergent results. This requirement has restricted a full quantal calculation to investigate heavy-particle

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Hydrogen–anti-hydrogen elastic scattering using fully quantal method

Sinha¹,

Ghosh

2000

Europhys. Lett.

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“…When the Br atom moves across a region with sufficiently small field, near the center of the magnetic trap, it can change from a low to a high-field seeking m j sub-level and is expelled from the trap. Majorana transitions may occur when the rate of change of the magnetic field experienced by the atom |dB/dt| exceeds the Larmor frequency ω L [15]. Substituting the notional time dependence of the magnetic field for its spatial gradient and the velocity of a trapped atom yields the inequality that must be satisfied for a Majorana transition to occur:…”

Section: Majorana Lossesmentioning

confidence: 99%

Collisional trap losses of cold magnetically trapped Br atoms

2014

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Near-threshold photodissociation of Br2 from a supersonic beam produces slow bromine atoms that are trapped in the magnetic field minimum formed between two opposing permanent magnets. Here, we quantify the dominant trap loss rate due to collisions with two sources of residual gas: the background limited by the vacuum chamber base pressure, and the carrier gas during the supersonic gas pulse. The loss rate due to collisions with residual Ar in the background follows pseudo firstorder kinetics, and the bimolecular rate coefficient for collisional loss from the trap is determined by measurement of this rate as a function of the background Ar pressure. This rate coefficient is smaller than the total elastic collision rate coefficient, as it only samples those collisions that lead to trap loss, and is determined to be νσ = (1.12±0.09)×10 −9 cm 3 s −1 . The calculated differential cross section can be used with this value to estimate a trap depth of 293 ± 24 mK. Carrier gas collisions occur only during the tail of the supersonic beam pulse. Using the differential cross section verified by the background-gas collision measurements provides an estimate of the peak molecular beam density of (3.0 ± 0.3) × 10 13 cm −3 in good agreement with the prediction of a simple supersonic expansion model. Finally, we estimate the trap loss rate due to Majorana transitions to be negligible, owing to the relatively large trapped-atom phase-space volume.

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“…The first antihydrogen atoms were produced at CERN by interactions of the relativistic antiproton beams with the hydrogen gas jet target; however, those atoms were not suitable for the studies mentioned above for their inadequacy and high velocities. Other experimental methods are applied, at CERN [6][7][8][9][10][11][12][13][14] and Fermilab [15], to H production. For example, cold H atoms have been produced by mixing trapped antiprotons with cold positrons [9].…”

Section: Introductionmentioning

confidence: 99%

The Faddeev approach applied to antihydrogen formation

Ghanbari-Adivi

2010

J. Phys. B: At. Mol. Opt. Phys.

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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.

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Cited by 14 publications

References 17 publications

Hydrogen–anti-hydrogen elastic scattering using fully quantal method

Hydrogen–anti-hydrogen elastic scattering using fully quantal method

Collisional trap losses of cold magnetically trapped Br atoms

The Faddeev approach applied to antihydrogen formation

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