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About Exotic Atoms
Exotic Atom (Mini) Reviews:
Pionic Hydrogen: Status and Outlook, D.F. Anagnostopoulos et al.
The measurement of the strong interaction shift and width of the ground state in the pionic hydrogen atom determines two different
linear combinations of the two isospin separated s-wave scattering lengths of the pion nucleon system. If both quantities are measured
with a precision of about 1%, a stringent test of chiral perturbation theory and a determination of the pion nucleon
coupling constant can be obtained. Past measurements determined the shift with an accuracy better than 1%,
and the width with an accuracy of 9%. Additional information from pionic deuterium measurements has been used
in order to extract isospin separated scattering lengths with sufficient accuracy. Future measurements plan to directly measure the width of
pionic hydrogen with an accuracy on the level on 1%.
Cascade in Muonic and Pionic Atoms with Z=1, V.E. Markushin.
Recent theoretical and experimental studies of the exotic atoms with Z=1 are reviewed. An interplay between the atomic internal and external
degrees of freedom is essential for a good description of the atomic cascade. The perspective of ab initio cascade calculations is outlined.
Atomic Cascade and X-ray yields in light exotic atoms, V.E. Markushin.
The atomic cascades in mu-p, pi-p, and K-p have been studied in detail using a new Monte Carlo kinetics code.
For the first time, a nuclear absorption in the atomic cascade was treated in a way fully consistent with the elastic scattering and
Stark mixing processes. This allowed us to get rid of tuning parameters commonly used in earlier calculations. An interplay between the
atomic internal and external degrees of freedom is shown to play an important role in the atomic cascade.
Light exotic atoms, D. Gotta
The new era in X--ray spectroscopy of exotic atoms is based on high--resolution reflection--type crystal spectrometers, state--of--the--art X--ray
detectors, and sophisticated set--ups to stop the negatively charged particles provided by modern accelerator facilities. Measurements on the
elementary systems formed with hydrogen and helium isotopes yield a precision unprecedented in low--energy strong--interaction physics.
Spin--spin and spin--orbit effects were identified in antiprotonic hydrogen and hadronic effects were observed for the first time in antiprotonic
deuterium. In kaonic hydrogen strong--interaction effects finally could be identified unambiguously. For the pion--proton and pion--deuteron system
the measurements reach an accuracy for the hadronic shift of a few per mill, which demands further theoretical effort to extract the scattering
lengths at the same level. To allow a precise determination of the pion--nucleon coupling constant, which constitutes a stringent test of the
approach for Quantum Chromodynamics in the non--perturbative regime, a new series of measurements has been started aiming at an accuracy
of 1\% for the hadronic width in pionic hydrogen. The mass of the charged pion was re--measured by using light pionic and muonic atoms and
the first direct observation of Coulomb explosion was achieved for exotic atoms. Tests of bound--state Quantum Electrodynamics became
possible at an accuracy which in turn can be used now to establish X--ray standards in the few keV range by the pionic atoms themselves.
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