Abstract: Quasicrystals are exotic materials with symmetries once thought to be impossible for matter. This talk will describe the decades-long adventures searching for them...
Oct21
Abstract: Neutrinos, the only neutral elementary fermions, have provided many surprises. Flavor oscillations reveal the non-conservation of the lepton flavor number and demonstrate that neutrino masses are finite; yet they are surprisingly much smaller than those of other fermions (by at least six orders of magnitude!) It is then natural to ask if the mechanism providing the mass to neutrinos is the same that gives masses to the other (charged) elementary fermions and if neutrinos are described by 4-component Dirac wavefunctions or, as is possible for neutral particles, by 2-component Majorana ones.
The hypothetical phenomenon of neutrino-less double-beta decay can probe the Majorana nature of neutrinos and the conservation of the total lepton number. It may also help elucidating the origins of mass in the neutrino sector. This is the Frontier of neutrino physics.
Following the well-known principle that there is no free lunch in life, interesting half-lives for neutrino-less double-beta decay exceed 1025 years (or ~1015 times the age of the Universe!) making experiments rather challenging. I will describe nEXO, a 5-tonne, enriched Xenon experiment with a sensitivity reaching beyond 1028 years, or >100 times the current state of the art. The nEXO detector derives directly from EXO-200, a very successful, rogue detector built by a collaboration with a heavy SLAC-Stanford participation.
About Prof. Giorgio Gratta
Giorgio Gratta is a Professor of Physics at Stanford university and the current Physics department chair. Gratta is an experimentalist, with research interests in the broad area of the physics of fundamental particles and their interactions. While his career started with experiments at particle colliders, since at Stanford Gratta has tackled the study of neutrinos and gravity at the shortest distances.
With two landmark experiments using neutrinos produced by nuclear reactors, Gratta and collaborators investigated the phenomenon of neutrino flavor mixing, in one case reporting the first evidence for neutrino oscillations using artificial neutrinos. This established the finite nature of neutrino masses. The same experiment was also first to detect neutrinos from the interior of our planet, providing a new tool for the Earth sciences.
As a natural evolution from the discovery of neutrino oscillations, Gratta has led the development of liquid Xenon detectors in the search for the neutrinoless double beta decay, an exotic nuclear decay that, if observed, would change our understanding of the quantum nature of neutrinos and help explaining the asymmetry between matter and antimatter in the universe. Gratta is currently the scientific leader of one of the three very large experiments on the subject, world-wide.
In a rather different area of research, Gratta’s group is studying new long range interactions (or an anomalous behavior of gravity) at distances below 50 micrometers. This is achieved with an array of different techniques, from optical levitation of microscopic particles in vacuum, to the use of Mössbauer spectroscopy and, most recently, neutron scattering on nanostructured materials.
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