Coulomb de-excitation of mesic hydrogen

Bracci, L.; Fiorentini, G.

doi:10.1007/bf02729003

Cited by 98 publications

(75 citation statements)

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“…Bracci and Fiorentini [12] calculated the Coulomb cross-sections for muonic hydrogen scattering from atomic hydrogen in a semiclassical model. Though the approach [12] may be unsuitable for treating the low n states, where more elaborate calculations give much smaller values for the cross-sections [13], it can be expected to give a fair description of the high n region. In the case of Stark mixing we use the fixed field model [14] for comparison.…”

Section: Resultsmentioning

confidence: 99%

Collisional deexcitation of exotic hydrogen atoms in highly excited states

Jensen

Markushin

2002

Eur. Phys. J. D

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Abstract. The deexcitation of exotic hydrogen atoms in highly excited states in collisions with hydrogen molecules has been studied using the classical-trajectory Monte Carlo method. The Coulomb transitions with large change of principal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n. The molecular structure of the hydrogen target is shown to be essential for the dominance of transitions with large ∆n. The external Auger effect has been studied in the eikonal approximation. The resulting partial wave cross-sections are consistent with unitarity and provide a more reliable input for cascade calculations than the previously used Born approximation.PACS. 34.50.-s Scattering of atoms and molecules -36.10.-k Exotic atoms and molecules (containing mesons, muons, and other unusual particles)

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Section: Resultsmentioning

confidence: 99%

Collisional deexcitation of exotic hydrogen atoms in highly excited states

Jensen

Markushin

2002

Eur. Phys. J. D

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“…All µAu time spectra exhibit a wide distribution whose maximum corresponds to µp kinetic energies E kin of 5...20 eV. Such energies result from Coulomb deexcitations [23] µp n +H 2 → µp n ′ <n + E kin + p + ... during the cascade, a well known effect for µp and πp atoms [9].…”

Section: Smentioning

confidence: 99%

Observation of Long-Lived Muonic Hydrogen in the2SState

Pohl¹,

Daniel²,

Hartmann³

et al. 2006

Phys. Rev. Lett.

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The kinetic energy distribution of ground state muonic hydrogen atoms µp(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keVcomponent is discovered and attributed to radiationless deexcitation of long-lived µp(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1 %, and a pressuredependent lifetime (e.g. 30.4 +21.4 −9.7 ns at 64 hPa) of the long-lived µp(2S) population, equivalent to a 2S-quench rate in µp(2S)+H2 collisions of 4.4 +2.1 −1.8 × 10 11 s −1 at liquid hydrogen density.PACS numbers: 36.10. Dr, 34.20.Gj A measurement of the Lamb shift in muonic hydrogen, i.e. the energy difference of 0.2 eV between the 2P -and 2S-states of µ − p atoms [1,2,3], is in progress at the Paul Scherrer Institute (PSI), Switzerland [4]. Vacuum polarization shifts the 2S-levels by 0.2 eV below the 2P -levels; fine and hyperfine splittings of the n = 2 levels are much smaller. The finite size effect is 2 % of the Lamb shift.The µp Lamb shift experiment is expected to give a precise value for the root-mean-square charge radius of the proton [5]. Together with recent advances in H-atom spectroscopy [6,7], this leads to a better determination of the Rydberg constant, and to a test of bound-state quantum electrodynamics on a new level of precision [8].The most important prerequisite for such an experiment, the availability of sufficiently long-lived µp(2S) atoms, has so far not been experimentally established. When muons are stopped in H 2 gas, µp atoms are formed at high n-levels and then deexcite predominantly to the ground state ("muonic cascade"). A fraction ε 2S of a few percent reaches the metastable 2S state whose lifetime is, in absence of collisions, essentially given by the muon lifetime of 2.2 µs.In a gas, there is collisional 2S-quenching, with very different rates depending on the µp kinetic energy being above or below the 2S-2P threshold (≈ 0.3 eV in the lab frame) [9]. Most µp(2S) atoms are formed at energies above this threshold [10], where collisional 2S → 2P Stark transitions (followed by 2P → 1S radiative deexcitation) lead to rather fast 2S-depletion. This is the "short-lived" 2S-component with a predicted lifetime [11] τ short 2S∼ 100 ns/p H2 [hPa]. There is, however, a competition between such Stark transitions and deceleration [9]. A fraction of the µp(2S) atoms should therefore survive the process of slowing down below 0.3 eV, where transitions to the 2P state are energetically forbidden. These µp(2S) atoms form the "long-lived" 2S-component, with a lifetime τ long 2S and a population ε long 2S (per µp atom).The 2S-population ε 2S is well determined from the measured µp X-ray yields [12,13,14]. ε long 2S can be derived from the measured 1S kinetic energy distributions [15] by using calculated elastic and inelastic µp(2S) cross sections [9]. At 16 hPa, for example, ε 2S = (4.40 ± 0.17) % and ε long 2S = (1.16 ± 0.12) %. Calculations of the radiative quenching process during collisions [16,17,18] predicted v...

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“…The theoretical study of the CD has also a long history (e.g., see [21][22][23][24][25][26][27]). Nevertheless, in the most important region n = 2 − 8 of the principal quantum number, relevant for the kinetics of the atomic cascade, this process has been regarded as the least studied until last decade [28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

“…However, this approximation can not be justified for low-energy scattering (see [19]). Thus, the latter approach as well as various modifications of the semiclassical model [5,6,20] lead to unreliable results in the low-energy region where only the lowest partial waves are important.The theoretical study of the CD has also a long history (e.g., see [21][22][23][24][25][26][27]). Nevertheless, in the most important region n = 2 − 8 of the principal quantum number, relevant for the kinetics of the atomic cascade, this process has been regarded as the least studied until last decade [28][29][30][31].…”

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confidence: 99%

Isotopic effects in scattering and kinetics of the atomic cascade of excited μ−p and μ−d atoms

Popov

Pomerantsev

2017

Phys. Rev. A

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The isotopic effects in the scattering and the kinetics of the atomic cascade of excited µ − p and µ − d atoms The quantum-mechanical calculations of the differential and integrated cross sections of the elastic scattering, Stark transitions, and Coulomb de-excitation at collisions of excited µ − p and µ − d atoms with hydrogen isotope atoms in the ground state are performed. The scattering processes are treated in a unified manner in the framework of the close-coupling approach. The used basis includes both open and closed channels corresponding to all exotic atom states with principal quantum numbers from n = 1 up to nmax = 20. The energy shifts of ns states due to electron vacuum polarization and finite nuclear size are taken into account. The kinetics of atomic cascade of µ − p and µ − d atoms are studied in a wide range of relative target densities (ϕ = 10 −8 − 1) within the improved version of the extended cascade model, in which the results of the numerical quantum-mechanical calculations of the cross sections for quantum numbers and kinetic energies of muonic atoms, that are of interest for the detailed cascade calculations, are used as input data. Initial (n, l, E)-distributions of muonic atoms at the instant of their formation and the target motion are taken into account explicitly in present cascade calculations. The comparison of the calculated cross sections, the kinetic energy distributions of muonic atoms at the instant of their np → 1s radiative transitions as well as the absolute and relative x-ray yields for both muonic hydrogen and muonic deuterium reveals the isotopic effects, which, in principal, may be observed experimentally. The present results are mainly in very good agreement with experimental data available in the literature.PACS numbers: I. INTRODUCTIONThe muonic and hadronic hydrogen-like atoms (µ) are formed in highly-excited states, when a heavy negatively charged particle (µ − , π − , K − , etc.) is slowed down in the gaseous or liquid hydrogen target and captured on the atomic orbit. After the exotic atom formation, its initial distributions in quantum numbers and kinetic energy are changed during the so-called atomic cascade through a number of processes: radiative and Stark transitions, elastic scattering, external Auger effect, Coulomb de-excitation (CD), weak decay, and strong absorption in the case of hadronic atoms.The general features of these exotic atoms are similar to ones of ordinary hydrogen atoms, because their level structure is mainly determined by the static Coulomb interaction. However, due to significant differences of exotic particle and electron masses, the distance scale in the exotic atom case is much smaller, while the energy scale is much larger in comparison with the usual atomic scale. These scale effects make possible to realize the processes of external Auger effect and CD and open additional opportunities for study of the quantum electrodynamics, weak or strong interactions (in the case of hadronic atoms), and scattering processes in collisions of the...

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Coulomb de-excitation of mesic hydrogen

Abstract: ..

Cited by 98 publications

References 6 publications

Collisional deexcitation of exotic hydrogen atoms in highly excited states

Collisional deexcitation of exotic hydrogen atoms in highly excited states

Observation of Long-Lived Muonic Hydrogen in the2SState

Isotopic effects in scattering and kinetics of the atomic cascade of excited μ−p and μ−d atoms

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