Precision spectroscopy of light exotic atoms
Abstract
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 could finally 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.
- Publication:
-
Progress in Particle and Nuclear Physics
- Pub Date:
- March 2004
- DOI:
- 10.1016/j.ppnp.2003.09.003
- Bibcode:
- 2004PrPNP..52..133G
- Keywords:
-
- Exotic atoms;
- Antiprotonic atoms;
- Kaonic atoms;
- Pionic atoms;
- Light hadronic atoms;
- Low-energy strong interaction;
- Pion mass;
- Bound-state QED;
- Exotic-atom cascade;
- Crystal spectrometer;
- X-ray detection;
- X-ray standards;
- Fluorescence X-rays