Collisional deexcitation of exotic hydrogen atoms in highly excited states

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)

Observation of Long-Lived Muonic Hydrogen in the2SState

“…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].…”

“…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.…”

“…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.…”

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

“…In the present paper we use as the improved version of the ESCM originally developed in [11] and later essentially improved in the paper [12] and in recent papers [31,52,53]. The improvements were mainly achieved due to new theoretical results for the cross sections of the collisional processes and initial distributions of muonic atoms in the quantum numbers and the laboratory kinetic energy at the instant of their formation.…”

“…The extended standard cascade model (ESCM) [11,12] introduces a number of improvements compared to the earlier models: for example, the scattering from molecular hydrogen at high n is calculated as opposed to the phenomenological treatment in other cascade models. Cascade calculations in this model include the evolution of the kinetic energy during de-excitation cascade.…”