Long-lived states of antiprotonic lithiump¯Li+produced inp¯

Abstract

Antiproton capture by lithium atoms (p + Li →pLi + + e) is investigated at collision energies from 0.01 to 10 eV by using a semiclassical (also know as quantum-classical hybrid) method, in which the radial distance between the antiproton and the Li + ion is treated as a classical variable, and the other degrees of freedom are described by quantum mechanics. Analyzing the wave packet of the emitted electrons and making use of the energy conservation rule enable us to calculate the state distribution of the produced antiprotonic lithiumpLi + atoms and also to distinguish between the capture and ionization (→p + Li + + e) channels at collisional energies above the ionization threshold. This method is tested for the capture of negative muons by hydrogen atoms, which was rigorously investigated in previous quantum mechanical studies. Most of thepLi + atoms produced inp + Li are found to be sufficiently stable against Auger decays and are experimentally observable as long-lived states. The present system bears close similarities to the system ofp + He(2S). It is therefore expected that long-lived antiprotonic heliumpHe + atoms can be efficiently produced in thep capture by metastable He(2 3 S) atoms.

Formation of antiprotonic heliump¯He+and ionization in low-energy collisions ofp¯with He in the groundSakimoto1 2015Phys. Rev. ASelf Cite

“…For p + H, agreement between the SC and QM results for the reactive cross sections is good at collision energies both below and above the ionization threshold [22,26], In Ref. [12], the adequacy of the SC method for calculating the distribution of the product states was further established by making a comparison between the SC and QM results for negative muon (p~) capture by H. Thus, the SC method is expected to be sufficiently useful for the present purpose. Unfortunately, an accurate treatment of two electrons is still quite difficult even within the SC approximation.…”

“…Other than near-circular states, the possibility of the exis tence of long-lived antiprotonic atoms has been suggested by several workers [8][9][10][11][12]: The Auger transition can be strongly suppressed whenever the angular momentum of the p orbital is sufficiently high. Such high-angular-momentum states can be produced in p capture by Li [10][11][12], where the 2s electron is involved.…”

“…In contrast to the QM calculation [25], which is limited to the capture process at low collision energies, also considered here is breakup ionization, p + He ->• p + He+ + e, which becomes open at energies above the first ionization threshold. The SC method has been applied to the p + H [26] and p + Li [12] systems, but apparently not yet to the p + He system. For p + H, agreement between the SC and QM results for the reactive cross sections is good at collision energies both below and above the ionization threshold [22,26], In Ref.…”

“…The present paper investigates in detail p capture by He in the ground (1 'S') and metastable (2 3S and 2 'S') states by using a semiclassical (SC) method [ 12,26], in which the radial distance between p and He2+ is treated as a classical variable, and the other degrees of freedom are fully described by quantum mechanics. In contrast to the QM calculation [25], which is limited to the capture process at low collision energies, also considered here is breakup ionization, p + He ->• p + He+ + e, which becomes open at energies above the first ionization threshold.…”

“…Such high-angular-momentum states can be produced in p capture by Li [10][11][12], where the 2s electron is involved. Although the same situation is expected to occur for the He target in excited metastable 2S states [9,12], no further investigation appears to have been made yet of p capture by metastable He.…”