**The Atomic Physics Group**

**Faculty: Sapirstein
Emeritus Faculty: **

**Berry - Johnson - Livingston - Tanner**

**Experimental Program**

The experimental atomic physics program at Notre Dame is directed toward the study of the structure, excitation, and de-excitation characteristics of atoms and ions. This work stimulates advances in the theoretical understanding of atomic systems at the most fundamental level, where relativistic and field-theoretic aspects of the atoms become important.

An experimental laser spectroscopy program focuses on precision measurements of transition amplitudes and energies. These measurements are of interest to the study of parity nonconservation effects in atoms which is motivated by the study of weak interactions and are part of a low energy test of the standard model. High-resolution spectroscopic techniques are also used in other applications. This program involves the use of tunable dye lasers and diode lasers.

Highly stripped heavy-ion beams of 10-100 MeV energy are produced at the accelerator facilities of the Nuclear Structure Laboratory. Experiments are also performed at other off-site heavy-ion accelerators. Present investigations concentrate on the precision atomic spectroscopy of highly ionized atoms and the measurement of lifetimes of selected atomic states in these ions. The spectroscopic measurements test current relativistic and quantum electro-dynamic calculations of atomic structure for few-electron ions. The lifetime results reflect the effects of both electron correlations and relativistic contributions in the de-excitation rates of excited atomic states. These data are also important to the diagnostics and modeling of high-temperature astrophysical and laboratory plasmas.

**Theoretical Program**

Notre Dame atomic theorists work on problems at the interface of atomic and particle physics. Recently, they have been involved in calculations of electron electric dipole moment enhancement factors in heavy rare-earth ions in support of experiments to detect time-reversal (T) violation. The atomic theory group produced the most accurate available prediction of parity nonconserving (PNC) amplitude in cesium, which, when combined with experiment, served as a stringent test of the standard model. Systematic calculations of the PNC amplitudes induced by the nuclear anapole moment have also been carried out. Recently, the atomic theory group calculated isotope shifts in ions of interest in the search for time-variation of the fine-structure constant. Higher-order corrections to quantum field theories for hydrogen, helium, and positronium are other subjects of current investigations. In a different but related atomic theory project, ab initio studies of transport properties of warm-dense plasmas are underway.