Special Seminars 2015

Abstract

Abstract

Cold atoms and ions are exciting systems for a variety of measurements of fundamental physics. Radio frequency traps open up experiments with both large ensembles of ions, e.g. in cold chemistry, and experiments with few or single ions, such as in quantum computations/simulations or optical clocks, where ultimate quantum control matters. Optical traps enable complementary experiments with neutral atoms.
I will first describe recent results from our work on cold chemistry and cold molecular ions using a hybrid atom ion. We have developed an integrated time-of-flight mass spectrometer, which allows for the analysis of the complete ion ensemble with isotopic resolution. With this new ability, we have significantly enhanced previous studies of cold reactions and found unexpected, new reactions. Further, we demonstrated a proof-of-principle implementation of non-equilibrium physics in our hybrid trap. Current work aims at demonstrating rotational cooling of molecular ions.
Next, I will report our recent results in the search for the nuclear isomeric transition in thorium-229. This transition, in the vacuum-ultraviolet regime (around 7.8 eV) is better isolated from the environment than electronic transitions making it a very promising candidate for future precision experiments, such as a nuclear clock and tests of fundamental constants. Our approach employs a direct search with thorium-doped crystals. In a first experiment with synchrotron radiation (ALS, LBNL), we were able to exclude a large region of possible transition frequencies and lifetimes. Currently, we continue our efforts with enhanced sensitivity using a pulsed VUV laser system. Additionally, theoretical considerations of possible transition energies and lifetimes will be presented.

Abstract

Abstract

Despite the tremendous progress in understanding the fundamental properties of neutrinos over the past decades, several key questions remain unanswered. In particular, we do not yet know if neutrinos are Majorana particles (i.e., are neutrinos and antineutrinos identical?). The most sensitive experimental probe of the Majorana nature of the neutrino is to search for the lepton-number violating neutrino-less double-beta decay (0νββ). A positive observation of this decay mode would confirm that neutrinos are Majorona particles and could allow the determination of the absolute neutrino mass scale from the half-life of the decay. EXO-200 is currently searching for the existence of 0νββ decays in ¹³⁶Xe, and has provided one of the most sensitive limits on the half-life of this decay (T_1/2 > 1.1 x 10²⁵ yr at 90% C.L.). In order to increase sensitivity to this decay it is necessary to further suppress the background (currently dominated by gamma rays) and increase the mass of the parent isotope under observation. The next generation of this experiment, nEXO, has started development of a multi-ton scale time-projection chamber to continue the search for 0νββ decays. In contrast to the search for 0νββ in other isotopes, a xenon detector offers the possibility to extract the Ba-daughter ions and identify them. Successful identification of the Ba-daughter of the decay would allow nearly all gamma backgrounds to be eliminated, greatly increasing the sensitivity of next-generation searches for 0νββ.
The status of Ba-ion extraction from a high pressure Xe gas environment will be presented, along with the latest results from EXO-200 and the future prospects of nEXO.