Relativistic Quantum Chemistry and Spectroscopy of Kaonic Atomic Systems …
35
and natural widths of the levels with a precision of few meV [1–27]. For a long time
the similar experimental investigations have been carried out in the laboratories of
Berkley, Virginia (USA), CERN (Switzerland) etc.
The mechanism of creation of the hadronic (kaonic) atoms is well known now
(e.g., [1–5]). Really, such an atom is formed when a negative kaon (pion) enters a
medium, looses its kinetic energy through excitation and ionization channels and
eventually is captured, replacing the electron in an excited atomic orbit. The further
de-excitation scenario includes the different cascade processes such as the Auger
transitions, Coulomb de-excitation, scattering etc. When a kaon reaches a low-n
state with the little angular momentum, strong interaction with the nucleus causes
its absorption.
The strong interaction is the reason for a shift in the energies of the low-lying
levels from the purely electromagnetic values and the finite lifetime of the state
corresponds to an increase in the observed level width. At present time several highly
precise measurements are carried out for the kaonic (pionic) hydrogen, helium and
other elements, including heavy systems. The E570 experiment [18, 19] allowed to
make the precise measurement of the X-ray energies in the kaonic helium atom. For
this system during the last decades a very complicated situation takes place. Speech
is about a large discrepancy between the theories and experiments on the kaonic
helium 2p state.
At the beginning of the 1970s and 80s several experimental groups (WG71Wiegand–Pehl (1971), BT79-Batty et al. (1989); e.g. [1–26]) declared relatively large
repulsive shift (~−40 eV), while the physically reasonable optical models calculations give shift less on the order. This sharp disagreement between the experimental
and theoretical results received a status of the “kaonic helium puzzle”. In Fig. 1 the
Experimental K–He spectrum (Okada et al. 2007; E570 exp. At KEK 12 GeV proton
synchrotron RIKEN Nishina Center, JAPAN) is presented (from Refs. [18, 19]).
Much larger shift was predicted in the theory with assuming the existence of the
deeply bound kaonic nuclear states. Several theoretical estimates of the last years
(look e.g. [18, 19]) did not confirm the large shift in the kaonic helium. The new
measurement of the kaonic helium X-ray was performed using the KEK-PS K5 kaon
beam channel in 2005.
The widely applied theoretical approaches to study of the hadronic (kaonic and
other) atomic systems are described in Refs. [1–56]. In Refs. [43–56] the effective
ab initio schemes to the Klein-Gordon-Fock equation solution and further determination of the X–ray spectra for multi-electron kaonic atoms are presented with
the different schemes for accounting of the nuclear, QED, interparticle correlation
effects. The theoretical studying the strong interaction shifts and widths from X-ray
spectroscopy of kaonic atoms (U, Pb etc.) was fulfilled.
The most difficult aspects of the theoretical studying are reduced to the correct
description of the kaon (pion)-strong interaction as the electromagnetic part of the
problem is reasonably taken into consideration [2, 41–45, 57–68]. Besides, quite new
aspect is linked with the possible, obviously, very tiny electroweak and hyperfine
interactions.
35
and natural widths of the levels with a precision of few meV [1–27]. For a long time
the similar experimental investigations have been carried out in the laboratories of
Berkley, Virginia (USA), CERN (Switzerland) etc.
The mechanism of creation of the hadronic (kaonic) atoms is well known now
(e.g., [1–5]). Really, such an atom is formed when a negative kaon (pion) enters a
medium, looses its kinetic energy through excitation and ionization channels and
eventually is captured, replacing the electron in an excited atomic orbit. The further
de-excitation scenario includes the different cascade processes such as the Auger
transitions, Coulomb de-excitation, scattering etc. When a kaon reaches a low-n
state with the little angular momentum, strong interaction with the nucleus causes
its absorption.
The strong interaction is the reason for a shift in the energies of the low-lying
levels from the purely electromagnetic values and the finite lifetime of the state
corresponds to an increase in the observed level width. At present time several highly
precise measurements are carried out for the kaonic (pionic) hydrogen, helium and
other elements, including heavy systems. The E570 experiment [18, 19] allowed to
make the precise measurement of the X-ray energies in the kaonic helium atom. For
this system during the last decades a very complicated situation takes place. Speech
is about a large discrepancy between the theories and experiments on the kaonic
helium 2p state.
At the beginning of the 1970s and 80s several experimental groups (WG71Wiegand–Pehl (1971), BT79-Batty et al. (1989); e.g. [1–26]) declared relatively large
repulsive shift (~−40 eV), while the physically reasonable optical models calculations give shift less on the order. This sharp disagreement between the experimental
and theoretical results received a status of the “kaonic helium puzzle”. In Fig. 1 the
Experimental K–He spectrum (Okada et al. 2007; E570 exp. At KEK 12 GeV proton
synchrotron RIKEN Nishina Center, JAPAN) is presented (from Refs. [18, 19]).
Much larger shift was predicted in the theory with assuming the existence of the
deeply bound kaonic nuclear states. Several theoretical estimates of the last years
(look e.g. [18, 19]) did not confirm the large shift in the kaonic helium. The new
measurement of the kaonic helium X-ray was performed using the KEK-PS K5 kaon
beam channel in 2005.
The widely applied theoretical approaches to study of the hadronic (kaonic and
other) atomic systems are described in Refs. [1–56]. In Refs. [43–56] the effective
ab initio schemes to the Klein-Gordon-Fock equation solution and further determination of the X–ray spectra for multi-electron kaonic atoms are presented with
the different schemes for accounting of the nuclear, QED, interparticle correlation
effects. The theoretical studying the strong interaction shifts and widths from X-ray
spectroscopy of kaonic atoms (U, Pb etc.) was fulfilled.
The most difficult aspects of the theoretical studying are reduced to the correct
description of the kaon (pion)-strong interaction as the electromagnetic part of the
problem is reasonably taken into consideration [2, 41–45, 57–68]. Besides, quite new
aspect is linked with the possible, obviously, very tiny electroweak and hyperfine
interactions.