Atomic core-polarization effects in metastable hadronic helium atoms

Abstract

A theoretical consideration is presented concerning the atomic core-polarization effect on the E1 transitions of large-I circular orbitals in hadronic helium atoms (e X He~+), where the e occupies the 1s orbital and the negative hadron (X ) occupies a large-1 circular orbital. The first-order mixing of the 2p electron configuration due to the repulsive e -X interaction gives rise to a substantial suppression (-3) of the E1 transitions, compared with a single-particle estimate, since the slowly moving particle (X ) polarizes the electron cloud in the opposite direction. Recently discovered metastable states of antiprotonic helium atoms are discussed.

Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯Hori1, Eades2, Widmann3 et al. 2004Phys. Rev. A352230View full textAdd to dashboardCite

“…Of course, there are also contributions from Auger decay and radiative processes that change v ϵ n − l − 1, but calculations for a single isolated atom suggest that these contributions are all less than 10% [22,[30][31][32]. According to this model, the intensity I 1 ͑t 1 ͒ of the first spike [which is proportional to the population P ͑39,35͒ ͑t 1 ͒], and the intensity I 2 ͑t 1 , t 2 ͒ of the second spike [which contains information about the feeding into state ͑39, 35͒ from ͑40, 36͒ between t 1 and t 2 ] follow the analytical functions, The population evolution of state ͑39, 35͒ was measured using the pulsed (closed circles) and continuous (triangles) antiproton beams (d).…”

“…(ii) Thermalization: the pHe + atom initially recoils with roughly the same momentum as the incoming antiproton, but cools down within picoseconds by colliding with the surrounding helium atoms. (iii) Metastable cascade: The antiproton cascades down through several metastable levels by making successive radiative transitions with lifetimes =1−2 s, these being primarily of the type ⌬n = ⌬ᐉ = −1 that keeps the vibrational quantum number v ϵ n − ᐉ −1 [30][31][32] constant. The states can therefore be grouped into the cascade sequences v =0,1,2,3.... (iv) Auger decay: The antiproton finally reaches a short-lived state, from which Auger decay to an ionic state occurs within a few nanoseconds [8,22,33].…”

Systematic study of the decay rates of antiprotonic helium states

“…A prominent and important feature of the theoretically calculated Auger rates is their drastic dependence on the lowest possible transition multipolarity L, which is equal to the *Present address: Center for Nuclear Study (CNS), University of minimum angular momentum carried away by the Auger electron [10,12]. The theoretical rates are approximated by a rough estimation…”

“…In particular, the Auger rates ␥ A , which are dominant in the total decay rate for some pHe + states, have been calculated by many theorists [10][11][12][13] over a period of more than 30 years. The latest calculations with complex coordinate rotation (CCR) method by Korobov [7] and Kino [9] yield both real and imaginary parts of the complex energy at the same time, and the both parts are expected to have absolute precisions of the same order.…”

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

“…Due to the almost classical localization of the antiproton wavefunction for large-n states, transitions with n > 1 are much slower than those with n = 1, because the larger transition energies E n for n > 1 are outweighed by a m uch smaller overlap integral hfjE1jii of initial and nal state wavefunctions 13 . In the molecular picture, this means that the familiar selection rule v = ( n l 1 ) = 0 ; 1 for radiative transitions between low-lying vibrational states of an ordinary diatomic molecule is reduced to v = 0 in the case of pHe + due to the large angular momentum 14 .…”