Date/Time
Date(s) - 26/09/2007
3:15 pm - 4:15 pm

Title: Attosecond physics with neutrons and electrons: Compton scattering experiments

Speaker: Dr. C. Aris Chatzidimitriou-Dreismann

Institute: Technical University Berlin
Institute of Chemistry

Location: ABB 102

Description:

Several neutron Compton scattering (NCS, also called DINS) experiments [1,2] on liquid and solid samples containing protons or deuterons show a striking anomaly, which is a shortfall in the intensity of epitermal neutrons scattered by the protons and deuterons. E.g., neutrons colliding with water for just 100-500 attoseconds will see a ratio of hydrogen to oxygen of roughly 1.5 to 1, instead of 2 to 1 corresponding to the chemical formula H2O. The experiments were done at the ISIS neutron spallation facility, Rutherford Appleton Laboratory, UK. Due to the large energy and momentum transfers applied (ca. 4-50 eV) , the duration of a neutron-proton scattering event is a fraction of a
femtosecond, which is extremely short compared to condensed-matter relaxation times.
Recently this effect has been confirmed [2] using an independent method, electron-proton Compton scattering (ECS), at the Australian National University, Canberra. ECS experiments from a solid polymer showed the exact same shortfall in scattered electrons (with initial energy about 20-35 keV) from hydrogen nuclei, comparable to the shortfall of scattered neutrons in accompanying NCS experiments on the same polymer. The similarity of the results is striking because the two projectiles interact with protons via fundamentally different forces â??- electromagnetic and strong.
Theoretical considerations suggest the presence of short-lived quantum entanglement of the scattering protons and the surrounding electrons, so that the usual Born-Oppenheimer (BO) approximation and the associated concept of “effective BO potentials” are not applicable. The relevant physical frame for the theoretical treatment of the considered effect may be given by the quantum dynamics of open quantum systems, in which the phenomena of quantum entanglement and decoherence play a pivotal role.
Current electron scattering experiments on H2 and D2 in the gas phase (at McMaster University; in progress) with lower energy transfers indicate that the considered effect is present even in H2 molecules which remain intact after the electron-proton collision.