Special Seminars 2015
|Time:||Tuesday, 22 Dec 2015, 11:15|
|Place:||Central Seminar Room|
|Speaker:||Dr. Christian Schneider, UCLA/Los Angeles|
|Title:||Quantum control of atoms, ions, and nuclei|
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.
|Time:||Friday, 08 May 2015, 10:00 - 11:00|
|Place:||Seminar room Blaum|
|Speaker:||Thomas Brunner, Stanford University, Stanford CA, USA|
|Title:||Fishing in a sea of Xe - Searching for double-beta decay with nEXO|
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
(T1/2 > 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.