Search for positron quasibound states in the doubly excited region of the helium atom

Machacek, Joshua; Boadle, Roisin; Buckman, Stephen; Sullivan, James P.

doi:10.1103/physreva.86.064702

Cited by 13 publications

(11 citation statements)

References 12 publications

(17 reference statements)

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“…We have investigated the feasibility of producing positronatom bound states. There is a large amount of theoretical evidence supporting the existence of such states [99][100][101], but they have not yet been experimentally observed [102], in contrast to positron-molecule binding, which has been extensively studied [103]. Positron interactions with negative ions (e + + A − → e + A + e − ) [104] and photon-assisted recombination (e + + A + ν → e + A) [105] have been suggested as methods to produce positron-atom bound states.…”

Section: Discussionmentioning

confidence: 99%

Velocity selection of Rydberg positronium using a curved electrostatic guide

et al. 2017

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We report experiments in which a slow Rydberg positronium (Ps) beam was produced by velocity selection using a curved electrostatic quadrupole guide. Ps atoms in Rydberg-Stark states with principal quantum number n = 14 were prepared by a two-color optical excitation process in a uniform electric field. Low-field-seeking Stark states were produced at the entrance of a 0.6-m-long quadrupole guide that includes a 45 • bend, and were detected at the end of the guide via their annihilation γ radiation. The mean speed (kinetic energy) of atoms entering the guide was estimated to be ≈180 km s −1 (185 meV), whereas the mean longitudinal speed of guided atoms was measured via time of flight and found to be ≈90 km s −1 , equivalent to a kinetic energy of 45 meV. The measured transport data are in broad agreement with Monte Carlo simulations, which are also used to establish the efficacy with which the arrangement we describe could be used to perform Ps-atom scattering measurements.

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Section: Discussionmentioning

confidence: 99%

Velocity selection of Rydberg positronium using a curved electrostatic guide

et al. 2017

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“…An initial search for the e + He(2s 2 1 S e ) resonance in a positronhelium scattering experiment was not successful [20]. The present improved estimates of the positions and widths of these resonances might aid any future experimental effort.…”

Section: Introductionmentioning

confidence: 88%

“…The variation in the cross section for the creation of He + was only 1% over the width of the He − (2s 2 2p) resonance, and the number of counts per channel exceeded 100 000 000. The statistical uncertainty in the Machacek et al [20] experiment seems to be about 2% [20]. Higher signal to background ratios have been achieved in e − -He experiments that measure differential cross sections.…”

Section: Complex Rotation Calculationsmentioning

confidence: 94%

“…There has already been one attempt to detect these states in a positron-helium scattering experiment. Machacek et al [20] measured the total cross section and the net positronium cross section for impact energies between 57.2 and 58.1 eV and did not see any evidence of a resonance. This experiment used a modern trap based positron beam that can achieve an energy resolution of 50 meV or better [9,36].…”

Section: Complex Rotation Calculationsmentioning

confidence: 99%

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Positron attachment to the He(ns21Se) states

Mitroy

Grineviciute

2013

Phys. Rev. A

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Calculations based on the projection method and using explicitly correlated Gaussians are used to confirm the existence of positron attachment to two doubly excited states of helium. The e + He(2s 2 1 S e ) and e + He(3s 2 1 S e ) states have binding energies of 0.449 and 0.286 eV. These estimates of the resonance energies are nearer to the variational limit than previous calculations. These states will exist as resonances in the e + -He scattering continuum, and complex rotation calculations have been used to estimate their widths.

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“…The complex rotation method, applied to the lower lying state has yielded a resonance width of 68 meV, which matches the resolution currently available in positron beam technology. The experiment has been carried out but determined only the upper bound on the resonance strength [46].…”

Section: Introductionmentioning

confidence: 99%

S-wave resonances of positronic helium: all-electron study with the stabilization method

Strasburger¹

2018

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

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The positions and widths of six resonances in the positron−helium system, for the electronic spin singlet state, have been computed using the stabilization method. The penetrable, parameterdependent confining potential has been included in the Hamiltonian, and the energy eigenvalues have been obtained in the optimized, fixed basis of explicitly correlated Gaussian functions. Apart from four already known resonances below the threshold for the formation of positronium in its first excited state, a new one has been revealed below the energy of the S 4 1 state of the helium atom. The existence of the resonance formed by positron attachment to a doubly excited helium atom in the s 2 2 electron configuration has also been confirmed.

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Search for positron quasibound states in the doubly excited region of the helium atom

Cited by 13 publications

References 12 publications

Velocity selection of Rydberg positronium using a curved electrostatic guide

Velocity selection of Rydberg positronium using a curved electrostatic guide

Positron attachment to the He(ns21Se) states

S-wave resonances of positronic helium: all-electron study with the stabilization method

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