Shortest flashes of ultra-hot matter
Heavy ion collisions could produce Yoktosecond pulsesRead out
It only takes a few quadrillionths of a second to cross an atomic nucleus - such "yoktosecond" pulses could theoretically be generated by high-energy heavy ion collisions. Under certain circumstances, double pulses are generated, which could make the dynamics of atomic nuclei "visible". The calculations published in the Physical Review Letters now show the light emission of so-called quark-gluon plasmas, which arise in such collisions for extremely short periods of time.
For high-precision spectroscopy or structural investigations of molecules as short as possible light flashes with the lowest possible wavelength, so high photon energy required. At present, X-ray flashes can be reached experimentally for several attoseconds (trillionths of a second). Even shorter pulses with even higher photon energy would improve the temporal and spatial resolution, or even allow the investigation of even smaller structures such as atomic nuclei.
In so-called pump-probe experiments, fast movements are observed as in slow motion with two pulses following each other in exactly controllable distance. The first pulse stimulates the system under investigation, while the second pulse interrogates the time evolution since the first pulse. Calculations at the Max Planck Institute for Nuclear Physics now show that high-energy heavy ion collisions in large particle accelerators are suitable as light sources for the desired single and double pulses.
Matter state as right after the Big Bang
This is due to the remarkable properties of a quark-gluon plasma. The quark-gluon plasma is considered the state of matter that made up the universe immediately after the Big Bang. In it the temperatures are so high that even the building blocks of the atomic nuclei, the neutrons and protons, are broken up into their components, the quarks. Such a state of matter can today be realized in modern accelerator systems.
In the collision of heavy ions - atoms of heavy elements with electrons removed - with relativistic velocities, such a quark-gluon plasma of atomic nucleus size is formed for a few yoctoseconds. In addition to many other particles, it also generates photons with a few gigaelectronvolts of energy, so-called gamma radiation. These high-energy light flashes are as short as the lifetime of the quark-gluon plasma and consist of only a few photons. displayTemporal evolution of quark-gluon plasma. The two ions shown as colored disks collide along the bump axis (black double arrow). Picture (a) shows the time immediately after the collision. The plasma (orange area) emits light indicated by wavy arrows in all
Radiation first perpendicular to the direction of impact
The researchers have now simulated the expansion and internal dynamics of quark-gluon plasma over time. It turned out that the photons are not emitted in all directions, but preferably perpendicular to the direction of impact. If a detector looks almost along the bump axis, it receives practically nothing during this period, so it sees a double pulse overall.
By a suitable choice of impact geometry and observation direction, the double pulses can in principle be selectively varied. Thus, they open the possibility of future pump-probe experiments in the Yoktosekundenbereich at high energies. This could lead to a time-resolved observation of core processes. Conversely, a detailed analysis of the gamma-ray burst would allow for conclusions on the quark-gluon plasma.
(Max Planck Institute for Nuclear Physics, 06.10.2009 - NPO)