Research

For high-precision spatial and temporal studies e.g. of atoms, molecules and nuclei, short light flashes with high photon energy are required. Currently, x-ray flashes in the attosecond range are accessible experimentally. Here, we show that quark gluon plasmas produced in high-energy heavy ion collisions can be a source of light flashes of a few yoctoseconds duration - the time that light needs to traverse an atomic nucleus. In particular, we simulated the time-dependent expansion and internal dynamics of the quark-gluon plasma. The fast expansion of the plasma naturally leads to GeV photon emission on the yoctosecond time scale. But throughout the evolution, under certain conditions, a momentum anisotropy may form in the expanding plasma. This anisotropy leads to a preferential emission of photons perpendicular to the collision axis at intermediate times. A detector that is placed close to the collision axis would therefore detects a double pulse (see figure). By suitable choice of geometry of the setup and observing direction, the time delay between the two pulses can in principle be selectively varied. This could open up the possibility of future pump-probe experiments in the yoctosecond range at high energies, leading to a time-resolved observation of processes in atomic nuclei. Conversely, a detailed analysis of the gamma-ray flashes would allow to draw conclusions about the quark-gluon plasma.

The search for practical methods to change the internal state of atomic nuclei has been the subject of a number of investigation in the last years. In particular, isomer triggering refers to the possibility to excite the long-lived excited isomeric nuclear state to a higher level which is associated with freely radiating states and therefore releases the energy of the metastable state. Isomers are of interest in different contexts, for example, due to fascinating potential applications related to the controlled release of nuclear energy on demand, such as in nuclear batteries, or motivated by the fundamental challenge to understand the formation of isomers and their role in the evolution of the universe.
We have compared isomer triggering via photoabsorption to low-lying triggering levels with alternative mechanisms. We show that x-ray triggering is possible, but it turns out that among the possible isomer triggering mechanisms, the coupling to the atomic shell via the process of nuclear excitation by electron capture is the most efficient one. An experimental verification of our findings at the borderline of atomic and nuclear physics may be provided by upcoming ion storage ring facilities and ion beam traps which will commence operation in the near future.

The strong angular momentum in non-central heavy-ion collisions can lead to global quark polarization in a quark gluon plasma (QGP) through spin-orbit coupling. The global quark polarization can be transfered to a polarization of massive secondary particles like the Λ-hyperon. So far only an upper bound for the Λ-hyperon polarization has been found, but its result is affected by all stages of the collision to an unknown degree. Photons on the other hand are likely to leave a QGP without further interaction and thus provide a primary probe for thermodynamic properties of the QGP.
We have studied the possibility to detect global quark polarization using photons emitted from the QGP through Compton scattering of quarks q g → q γ (antiquarks correspondingly) and gluons, and annihilation of quarks and antiquarks, q bar(q) → g γ. We calculated the visibility of the photon polarization for various degrees of momentum anisotropy of the QGP that naturally arise due to its anisotropic expansion. We found that especially foranisotropies compressed along the beam axis and higher photon energies, global quark polarization is transfered efficiently to circular polarization of photons.

The direct interaction of nuclei with super-intense laser fields is studied. We show that present and upcoming high-frequency laser facilities, especially together with a moderate acceleration of the target nuclei to match photon and transition frequency, do allow for resonant laser-nucleus interaction. These direct interactions may be utilized for the model-independent optical measurement of nuclear properties such as the transition frequency and the dipole moment, thus opening the field of nuclear quantum optics. As ultimate goal, one may hope that direct laser-nucleus interactions could become a versatile tool to enhance preparation, control and detection in nuclear physics.