The axion is a well-motivated dark matter candidate, but is challenging to search for. We propose a new way to search for QCD axion and axion-like-particle (ALP) dark matter. Nuclei that are interacting with the background axion dark matter acquire time-varying CP-odd nuclear moments such as an electric dipole moment. In analogy with nuclear magnetic resonance, these moments cause precession of nuclear spins in a material sample in the presence of a background electric field. This precession can be detected through high-precision magnetometry. With current techniques, this experiment has sensitivity to axion masses below 10^-9 eV, corresponding to theoretically well-motivated axion decay constants around the grand unification and Planck scales. With improved magnetometry, this experiment could ultimately cover the entire range of masses below 10^-6 eV, just beyond the region accessible to current axion searches. A discovery in such an experiment would not only reveal the nature of dark matter and confirm the axion as the solution of the strong CP problem, but would also provide a glimpse of physics at the highest energy scales, far beyond what can be directly probed in the laboratory.
Organic molecules such as tetracene crystallize into solids that can be semiconductors, metals, or even superconductors. Although they were first developed over half a century ago, it is only fairly recently that the considerable promise that organic semiconductors hold as materials for electroncs, display technologies, and solar cells has begun to be realized. Lightweight, flexible, and inexpensive, these materials offer an attractive balance between cost and performance, complemented by versatility, and functionally accomplished by means of molecular design. I will review the physics of organic semiconductors and describe how their electronic and optical properties can be utilized in a variety of applications.
One of the highest priorities of present-day experimental particle and nuclear physics is to search for indications of physics which is not contained in the Standard Model. Precision measurements of quantities that are robustly predicted within the Standard Model are an important class of such searches. An example is a measurement of the proton's weak charge. The weak charge is the strength of the proton's vector coupling to the weak neutral current, and its value is a firm prediction of the Standard Model. Thus an experimental test of the prediction is well motivated as a search for new physics. A recently completed experiment at Jefferson Lab, Qweak, has the goal of making the first precision measurement of the weak charge, using parity-violating electron scattering from hydrogen at very low momentum transfer. The result from the first subset of data will be presented, as well as an overview of the data analysis for the full data set and prospects for the final result, which will provide a sensitivity to new physics at the multi-TeV scale.
THE ABSTRACT Neutrinoless double beta decay (0νββ) is a beyond-the-standard-model physics process in which a nucleus (A,Z) decays to (A,Z+2) with the emission of two electrons (but no neutrinos). Experimental searches for 0νββ are motivated by the access this process gives to testing any Majorana nature of neutrinos and lepton number non-conservation. This process is also a sensitive probe of the absolute neutrino mass scale. EXO (Enriched Xenon Observatory) is an experimental program searching for 0νββ decay of 136Xe. The first phase of the program, EXO-200, uses 200 kg of Xenon enriched to 80% in 136Xe, liquefied in a Time Projection Chamber (TPC) with scintillation readout (100 kg active mass), allowing for event calorimetry and 3D localization of ionizing events. EXO-200 has found the standard two-neutrino decay mode 2νββ of 136Xe, and has made a precision measurement of the (2.172±0.017[stat]±0.060[sys])×1021yr half. The collection of both light and charge signals and the reconstruction of event positions for both single and multi-cluster events allow background discrimination on top of the already low environmental background regime, and the possibility of studying events with extended topologies. A 5-tonne next generation liquid xenon experiment, nEXO, based on teh EXO-200 concept while implementing some notable innovations, is currently being designed. It promises to improve the sensitivity to improve the sensitivity to 0νββ of 136Xe by ~2 orders of magnitude and fully access the inverted hierarchy neutrino mass scale. This talk will discuss the detector performance and recent results from EXO-200 and present the nEXO experiment.
It has long been known that galaxies' internal structure is connected with their star formation activity in the nearby universe. Recent surveys have allowed us to study these correlations out to very large distances, allowing us for the first time to quantify these relationships over a significant span of cosmic time for statistically robust samples of objects. It has been known for several years that galaxies are growing in mass and radius, experiencing morphological transformation, and "downsizing" their star formation activity over cosmic time. Now, new observations are painting a picture in which the internal structure of galaxies (size and morphology) is intimately linked with their star formation activity and formation history. There are hints that the co-evolution of supermassive black holes with their host galaxies may be the driving force behind these correlations, but this remains controversial. While cosmological simulations set within the hierarchical formation scenario of Cold Dark Matter currently offer a plausible story for interpreting these observations, many puzzles remain. I will review recent insights gleaned from deep multi-wavelength surveys and state-of-the-art theoretical models and simulations, as well as highlight the open questions and challenges for the future.
There is increasing interest in thermoelectric materials motivated in part by recent progress and in part by the potential of these materials in various energy technologies. Thermoelectric performance is a multiply contra-indicated property of matter. For example, it requires (1) high thermopower and high electrical conductivity, (2) high electrical conductivity and low thermal conductivity and (3) low thermal conductivity and high melting point. The keys to progress are finding an optimal balance and finding ways of using complex electronic and phononic structures to avoid the counter-indications mentioned above. In this talk, I discuss some of the issues involved in the context of recent results. One key aspect is optimization of the doping level in a given thermoelectric material. While this has long been understood in terms of standard semiconductor parabolic band models, we find surprisingly different results for many thermoelectric materials when the actual first principles band structures are used. This has led to prediction of a number of useful thermoelectrics, some that are new, and surprisingly some that are old. This work was done in collaboration with David Parker, Xin Chen, Olivier Delaire and Mao-Hua Du and was supported by the Department of Energy through the S3TEC Energy Frontier Research Center.
In addition to providing vital clues as to the formation and evolution of black holes, the spin of black holes may be an important energy source in the Universe. Over the past couple of years, tremendous progress has been made in the realm of observational measurements of spin. I will describe these efforts with particular focus on the use of X-ray spectroscopy to probe the spin of supermassive black holes in active galactic nuclei (AGN). For the first time, we are obtaining hints about the distribution of spins across the population of supermassive black holes with some interesting and unexpected consequences. After discussing spin, I will also address questions related to the driving of relativistic jets from AGN and the jet-disk connection. I shall conclude by discussing future prospects enabled by Astro-H (to be launched in 2015) and LOFT/ATHENA+ (currently under consideration by ESA).
A permanent electric dipole moment (EDM) of a particle or system would arise due to breaking of time-reversal (T), or equivalently charge-conjugation/parity (CP) symmetry. Over the past five decades, a number of experiments on the neutron, atoms and molecules have only set upper limits on EDMs, and the search continues, motivated in large part by the expectation that beyond Standard-Model physics CP violation is required to explain the baryon asymmetry of the universe. In addition, new techniques and access to systems in which the effects of CP violation would be greatly enhanced are driving the field forward. Systems that may be favorable for significant advances include the isotopes 225Ra and 221/223Rn, where the combination of significant octupole collectivity and relatively closely spaced opposite parity levels would increase the nuclear Schiff moment by orders of magnitude compared to other diamagnetic atoms, i.e. 199Hg. A number of technical and nuclear-structure issues must be addressed in order to assess the prospects for an experiment of significant impact. Among the technical challenges for the Radon-EDM program are developing an on-line EDM experiment at an isotope-production facility that will collect and make measurements on the short-lived species (half lives are approximately 25 min). We have developed and tested a system for high-efficiency collection and spin-exchange polarization of noble-gas isotopes that has been tested at the TRIUMF ISAC facility (experiment S929). Radon polarization techniques were studied at ISOLDE and Stony Brook, and spin-precession detection techniques are under development. Nuclear-structure issues include determining the octupole collectivity as well as the spacing of opposite parity levels. A series of experiments at ISOLDE (IS475 and IS552) have recently directly measured octupole collectivity in 220Rn and 224Ra leading to strengthened confidence in conclusions about the octupole enhancements. Experiments are also underway at NSCL at Michigan State University TRIUMF/ISAC to study the nuclear structure of isotopes in this mass region. I will report on progress on all these fronts and discuss recent developments in our studies of how we learn about the basic physical parameters of CP violation from the suite of EDM measurements.
The first evidence for dark matter dates back to observations of the Coma cluster made by Fritz
Zwicky in 1933. Since that time, astrophysicists and astronomers have produced compelling evidence for the existence of dark matter and determined that it constitutes the bulk of the matter in the Universe. Despite this fact, the composition of the dark matter remains unknown. One compelling candidate for particle dark matter is the Weakly Interacting Massive Particle (WIMP). Working in a low-background environment in the Soudan Mine, located in northern Minnesota, the SuperCDMS experiment is designed to directly detect interactions between WIMPs and nuclei in its target Ge crystals. In this talk I will present the latest results from the SuperCDMS experiment. I will also discuss the current status of the SuperCDMS at Soudan experiment and plans for a future 200-kg scale experiment which is slated for operation in SNOLAB.
