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APS

Stark Transitions in Antiprotonic Helium

James Earl Russell

Published Oct 1, 2001• 0 citations
OpenAlex

Abstract

Collisional Stark rates for p 4 He + with 36≤n≤38 are estimated with coupled-channel calculations. Both an atomic and a molecular model are used. Matrix elements of the pHe + -He interaction for the atomic model are approximated with expressions having two or three parameters. Rough estimates for the molecular model are obtained using the generalized Born-Oppenheimer approximation, together with matrix elements for the atomic model. Guesswork, based on interactions of seemingly similar atoms, is used to set fairly wide limits to parameters for the atomic model, it being assumed that the potentials depend only on n, l, and R. Transitions are found to be unlikely. But the rates are sensitive to the potentials. Transitions can be likely if the potentials are different from what can reasonably be guessed by assuming a dependence on only n, l, and R. A potential with a minimum, preferably relatively deep, at relatively small R can cause transitions to be important. It is conjectured that this can occur because pHe + -He potentials depend on the component of pHe + intrinsic angular momentum along R. Also, it is found that the difference in the reduced mass of pHe + and He can cause the rate to be several times higher for p 3 He + than for comparable p 4 He + .

Related papers

Stark transitions in antiprotonic helium

James Earl Russell

Collisional Stark rates for ${p}^{4}{\mathrm{He}}^{+}$ with $36\ensuremath{\lesssim}n\ensuremath{\lesssim}38$ are estimated with coupled-channel calculations. Both an atomic and a molecular model are used. Matrix elements of the $\overline{p}{\mathrm{He}}^{+}\ensuremath{-}\mathrm{He}$ interaction for the atomic model are approximated with expressions having two or three parameters. Rough estimates for the molecular model are obtained using the generalized Born-Oppenheimer approximation, together with matrix elements for the atomic model. Guesswork, based on interactions of seemingly similar atoms, is used to set fairly wide limits to parameters for the atomic model, it being assumed that the potentials depend only on n, l, and R. Transitions are found to be unlikely. But the rates are sensitive to the potentials. Transitions can be likely if the potentials are different from what can reasonably be guessed by assuming a dependence on only n, l, and R. A potential with a minimum, preferably relatively deep, at relatively small R can cause transitions to be important. It is conjectured that this can occur because $\overline{p}{\mathrm{He}}^{+}\ensuremath{-}\mathrm{He}$ potentials depend on the component of $\overline{p}{\mathrm{He}}^{+}$ intrinsic angular momentum along $\mathbf{R}.$ Also, it is found that the difference in the reduced mass of $\overline{p}{\mathrm{He}}^{+}$ and He can cause the rate to be several times higher for ${p}^{3}{\mathrm{He}}^{+}$ than for comparable ${p}^{4}{\mathrm{He}}^{+}.$

Physical Review A•Feb 20, 2002•9 citations

Collisional Stark Transitions and Induced Annihilation of Cold Antiprotonic Helium Ions

Grigory Ya. Korenman, S. N. Yudin

Stark transitions and induced annihilation of antiproton in the collisions of antiprotonic helium ions (\bar{p}He^{+2})_{nl} with He atoms at very low energy (~ 10 K) are considered in the framework of quantum coupled-channels method taking into account all the states with different l at given n~30, including the annihilating ns and np-states. Elastic scattering, Stark transitions and induced annihilation during collisions are produced by scalar and dipole terms in the interaction. It is shown that the most important contribution to the processes comes from the long-range polarization interaction. Admixtures of the ns and np-states to the states with higher l during collisions induce the effective annihilation cross sections for the initial l up to 15, but don't affect the Stark cross sections for the initial states nearly to circular orbits. Total rates of the Stark transitions from the circular orbits with n=28 - 32, averaged over the thermal motion, are compatible with the recent ASACUSA data. Isotope effect as well as the dependence on n are also qualitatively agree with the experiment.

arXiv:0711.4505•Nov 28, 2007•0 citations

Low-energy antiproton interaction with helium

William R Gibbs

An ab initio potential for the interaction of the neutral helium atom with antiprotons and protons is calculated using the Born-Oppenheimer approximation. Using this potential, the annihilation cross section for antiprotons in the energy range 0.01 $\ensuremath{\mu}$eV to 1 eV is calculated.

arXiv:nucl-th/9705007•Physical Review A•Nov 1, 1997•8 citations

Collisions of cold antiprotonic helium atoms and ions with ordinary helium atoms

Grigory Ya. Korenman, S. N. Yudin

We consider two types of collisional processes with excited antiprotonic helium systems. (i) Transitions between hyperfine structure sublevels in ( He + ) n LFJ are considered at T ≤ 25 K using the coupled-channels method and a model of scalar and tensor interactions between antiprotonic and ordinary He atoms. Inelastic cross sections for the single and double spin-flip transitions are less than elastic ones by four and seven orders of magnitude, respectively. The cross sections show a resonance behaviour at E ∼ 1–4 K, and therefore the relaxation rates, density shift and broadening of the M1 spectral lines decrease with increasing temperature from 3 to 25 K. (ii) Stark transitions and induced annihilation during collisions of the ( He 2+ ) nl ion with He atoms at E ∼ 10 K are considered for all l -states at n ∼ 30 in the framework of the coupled-channels method. In order to take into account complex energy shifts of the ns and np -states, we introduce modified boundary conditions in these channels. The main contribution to elastic scattering, Stark transitions and induced annihilations during collisions comes from the long-range polarization interaction. Admixtures of ns and np -states to nl -states ( l ≥ 2) during collisions induce the effective annihilation cross sections for the initial l up to 15, but don't affect the Stark cross sections for states with nearly-circular orbits. The calculated values for both types of processes are compatible with recent experimental data.

Journal of Physics Conference Series•Nov 1, 2007•9 citations

Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms

Grigory Ya. Korenman, S. N. Yudin

Collisions of metastable antiprotonic helium with atoms of a medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between and He atoms. S -matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels ( F = L ± 1/2, J = F ± 1/2) of the nL level and relative angular momenta up to l = 5 at the kinetic energy E ≲ 25 K. The inelastic cross sections are less than elastic ones by four orders of value for the single electron or antiproton spin-flip transitions (Δ J = ±1, Δ F = 0, ± 1) and by seven orders of value for the double spin-flip transitions (Δ J = 0, ± 2, Δ F = ±1). The cross sections show a resonance behaviour at very low energy ( E ∼ 1–4 K). The results for the relaxation rate λ( F − → F + ), the frequency shift and broadening of the M1 spectral lines for the favoured transitions (Δ F = ±1, Δ J = ±1) are compatible with the recent experimental data obtained by a triple (laser–microwave–laser) resonance method at T = 6 K. The calculated values are lowered by a factor of 1.5–2 with the temperature rising up to 25 K.

arXiv:nucl-th/0411077•Journal of Physics B Atomic Molecular and Optical Physics•Mar 6, 2006•21 citations

Quenching of metastable states of antiprotonic helium atoms by collisions with H2 molecules

B. Ketzer, F. J. Hartmann, Till von Egidy +13 more

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were induced making use of state dependent quenching effects caused by trace admixtures of H2 to the target helium gas. With this method of “H2-assisted inverse resonances” the decay rates of the states (n,l)=(39,l),l=36,37,38, and (38,l),l=35,36,37 of p̄He+ were determined as a function of the H2 admixture. The quenching cross sections at 30 K deduced therefrom for the states with n=39 were found to be of the order of the geometrical cross section for p̄He+–H2 collisons (2⋅10−15 cm2), with a moderate decrease with increasing l. Within a given cascade with constant v=n−l−1, the quenching cross sections for states with n=38 are smaller by a factor of 4–6 than those for states with n=39.

The Journal of Chemical Physics•Jul 8, 1998•17 citations
Collisional Stark rates for p 4 He + with 36≤n≤38 are estimated with coupled-channel calculations. Both an atomic and a molecular model are used. Matrix elements of the pHe + -He interaction for the atomic model are approximated with expressions having two or three parameters. Rough estimates for the molecular model are obtained using the generalized Born-Oppenheimer approximation, together with matrix elements for the atomic model. Guesswork, based on interactions of seemingly similar atoms, is used to set fairly wide limits to parameters for the atomic model, it being assumed that the potentials depend only on n, l, and R. Transitions are found to be unlikely. But the rates are sensitive to the potentials. Transitions can be likely if the potentials are different from what can reasonably be guessed by assuming a dependence on only n, l, and R. A potential with a minimum, preferably relatively deep, at relatively small R can cause transitions to be important. It is conjectured that this can occur because pHe + -He potentials depend on the component of pHe + intrinsic angular momentum along R. Also, it is found that the difference in the reduced mass of pHe + and He can cause the rate to be several times higher for p 3 He + than for comparable p 4 He + .
Collisional Stark rates for p4He+{p}^{4}{\mathrm{He}}^{+}p4He+ with $36\ensuremath{\lesssim}n\ensuremath{\lesssim}38$ are estimated with coupled-channel calculations. Both an atomic and a molecular model are used. Matrix elements of the $\overline{p}{\mathrm{He}}^{+}\ensuremath{-}\mathrm{He}$ interaction for the atomic model are approximated with expressions having two or three parameters. Rough estimates for the molecular model are obtained using the generalized Born-Oppenheimer approximation, together with matrix elements for the atomic model. Guesswork, based on interactions of seemingly similar atoms, is used to set fairly wide limits to parameters for the atomic model, it being assumed that the potentials depend only on n, l, and R. Transitions are found to be unlikely. But the rates are sensitive to the potentials. Transitions can be likely if the potentials are different from what can reasonably be guessed by assuming a dependence on only n, l, and R. A potential with a minimum, preferably relatively deep, at relatively small R can cause transitions to be important. It is conjectured that this can occur because $\overline{p}{\mathrm{He}}^{+}\ensuremath{-}\mathrm{He}$ potentials depend on the component of p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ intrinsic angular momentum along R.\mathbf{R}.R. Also, it is found that the difference in the reduced mass of p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ and He can cause the rate to be several times higher for p3He+{p}^{3}{\mathrm{He}}^{+}p3He+ than for comparable p4He+.{p}^{4}{\mathrm{He}}^{+}.p4He+.
Stark transitions and induced annihilation of antiproton in the collisions of antiprotonic helium ions (\bar{p}He^{+2})_{nl} with He atoms at very low energy (~ 10 K) are considered in the framework of quantum coupled-channels method taking into account all the states with different l at given n~30, including the annihilating ns and np-states. Elastic scattering, Stark transitions and induced annihilation during collisions are produced by scalar and dipole terms in the interaction. It is shown that the most important contribution to the processes comes from the long-range polarization interaction. Admixtures of the ns and np-states to the states with higher l during collisions induce the effective annihilation cross sections for the initial l up to 15, but don't affect the Stark cross sections for the initial states nearly to circular orbits. Total rates of the Stark transitions from the circular orbits with n=28 - 32, averaged over the thermal motion, are compatible with the recent ASACUSA data. Isotope effect as well as the dependence on n are also qualitatively agree with the experiment.
We consider two types of collisional processes with excited antiprotonic helium systems. (i) Transitions between hyperfine structure sublevels in ( He + ) n LFJ are considered at T ≤ 25 K using the coupled-channels method and a model of scalar and tensor interactions between antiprotonic and ordinary He atoms. Inelastic cross sections for the single and double spin-flip transitions are less than elastic ones by four and seven orders of magnitude, respectively. The cross sections show a resonance behaviour at E ∼ 1–4 K, and therefore the relaxation rates, density shift and broadening of the M1 spectral lines decrease with increasing temperature from 3 to 25 K. (ii) Stark transitions and induced annihilation during collisions of the ( He 2+ ) nl ion with He atoms at E ∼ 10 K are considered for all l -states at n ∼ 30 in the framework of the coupled-channels method. In order to take into account complex energy shifts of the ns and np -states, we introduce modified boundary conditions in these channels. The main contribution to elastic scattering, Stark transitions and induced annihilations during collisions comes from the long-range polarization interaction. Admixtures of ns and np -states to nl -states ( l ≥ 2) during collisions induce the effective annihilation cross sections for the initial l up to 15, but don't affect the Stark cross sections for states with nearly-circular orbits. The calculated values for both types of processes are compatible with recent experimental data.
Collisions of metastable antiprotonic helium with atoms of a medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between and He atoms. S -matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels ( F = L ± 1/2, J = F ± 1/2) of the nL level and relative angular momenta up to l = 5 at the kinetic energy E ≲ 25 K. The inelastic cross sections are less than elastic ones by four orders of value for the single electron or antiproton spin-flip transitions (Δ J = ±1, Δ F = 0, ± 1) and by seven orders of value for the double spin-flip transitions (Δ J = 0, ± 2, Δ F = ±1). The cross sections show a resonance behaviour at very low energy ( E ∼ 1–4 K). The results for the relaxation rate λ( F − → F + ), the frequency shift and broadening of the M1 spectral lines for the favoured transitions (Δ F = ±1, Δ J = ±1) are compatible with the recent experimental data obtained by a triple (laser–microwave–laser) resonance method at T = 6 K. The calculated values are lowered by a factor of 1.5–2 with the temperature rising up to 25 K.
Laser resonance transitions between normally metastable states of antiprotonic helium atoms were induced making use of state dependent quenching effects caused by trace admixtures of H2 to the target helium gas. With this method of “H2-assisted inverse resonances” the decay rates of the states (n,l)=(39,l),l=36,37,38, and (38,l),l=35,36,37 of p̄He+ were determined as a function of the H2 admixture. The quenching cross sections at 30 K deduced therefrom for the states with n=39 were found to be of the order of the geometrical cross section for p̄He+–H2 collisons (2⋅10−15 cm2), with a moderate decrease with increasing l. Within a given cascade with constant v=n−l−1, the quenching cross sections for states with n=38 are smaller by a factor of 4–6 than those for states with n=39.