Events at Physics |
Events During the Week of April 12th through April 19th, 2009
Monday, April 13th, 2009
- High Energy Seminar
- A study of Z events produced at low transverse momentum using a novel technique
- Time: 4:00 pm - 4:00 pm
- Place: 4274 Chamberlin (Coffee and Cookies at 3:45 pm) i
- Speaker: Mika Vesterinen, University of Manchester
- Host: Matt Herndon
Tuesday, April 14th, 2009
- Chaos & Complex Systems Seminar
- Taking the pulse of the geodynamo
- Time: 12:05 pm
- Place: 4274 Chamberlin
- Speaker: Brad S. Singer, UW Department of Geoscience
- Abstract: During the past 2.6 million years Earth's outer core geodynamo has produced at least 18 geomagnetic excursions and 5 full polarity reversals. This record has been compiled from terrestrial volcanic rocks, including mainly basaltic lava flow sequences, but also two silicic ash beds, that have been analyzed using modern paleomagnetic techniques and dated using the 40Ar/39Ar variant of the K-Ar radio-isotopic clock. Several brief periods of field instability associated with excursions correlate with lows in paleointensity or directional changes recorded globally in marine sediments that are dated using astronomically-forced oxygen isotope signals or ice layer-counting. However, the lack of correlation of several excursions between marine and terrestrial records indicates that neither sediments, nor lava flows, are ideal recording media. Another factor complicating correlation is that some excursions may be geographically localized and not expressed globally. Despite decades of observation, these records remain fragmentary, especially when periods of millions of years are considered. Recent 40Ar/39Ar dating in our laboratory, that includes age determinations for the Mono Lake, Laschamp, Blake, Pringle Falls, Big Lost, West Eifel excursions, as well as the Halawa (C2r.2r-1) cryptochron, prompt us to critically review the terrestrial record of geodynamo instability and propose a Geomagnetic Instability Time Scale (GITS) for the Quaternary period. Both the ca. 4:1 ratio of excursions to reversals during the past 2.6 Ma as well as the temporal pattern of occurrence of these events provide fundamental input as to the long‑term behavior and, possibly, the structure of the core dynamo. On the one hand, intervals of significant temporal clustering of excursions have highlighted a relatively stable period of high field strength lasting >250,000 years in the middle of the Brunhes chron during which time few, or no, excursions took place. On the other hand, successive paleomagnetic excursion records may be critical in regard to understanding the behaviors and interactions between the mantle‑influenced field source in the shallow core (the hypothesized SCOR‑field) and the deeper‑held source of the axial dipole. If in fact a successful reversal attempt requires the axial dipole field source to be weakened below some threshold strength for substantial duration (ca. 10,000 ‑20,000 years), times of grouped excursions may also be the most probable times for a change in polarity.
- Astronomy Colloquium
- Polarized FIR Emission from T Tauri Disks
- Time: 3:30 pm - 5:00 pm
- Place: 6515 Sterling Hall
- Speaker: Jungyeon Cho, UW Astronomy Dept
- Abstract: Recently far infra-red (FIR) polarization of the 850 micron continuum emission from T Tauri disks has been detected. The observed degree of polarization is around 3 % or less. Since thermal emission from dust grains dominates the spectral energy distribution at the FIR regime, dust grains might be the cause of the polarization. In the presence of magnetic field, dust grains
can get aligned by radiative torque and the aligned grains can produce polarized emission in infrared wavelengths. We explore alignment of dust grains by radiative torque in T Tauri disks and provide predictions for polarized emission for disks viewed at different wavelengths and viewing angles. Our study indicates
that multi-frequency infrared polarimetric studies of protostellar disks can provide good insights into the details of their magnetic structure. We also introduce the result and implications of a more recent observation at 350 microns. - Host: Professor Alex Lazarian
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Recent Results from MINOS (Joint NPAC/HEP Seminar)
- Time: 4:00 pm
- Place: 5280 Chamberlin
- Speaker: Christopher White, Illinois Institute of Technology
- Abstract: MINOS (Main Injector Neutrino Oscillation Search) is a
mature neutrino experiment that has been accumulating data using the NuMI neutrino beam since 2005. Data from 7 x 1020 protons-on-target have been recorded, primarily in low-energy neutrino mode. An update on the charge-current analysis will be presented as well as the recent electron appearance result. Additional results will be briefly reviewed along with prospects for future running in anti-neutrino mode. - Host: Karsten Heeger
Wednesday, April 15th, 2009
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Electroweak phase transition in the U(1)'-extended MSSM
- Time: 4:00 pm - 5:00 pm
- Place: 4274 Chamberlin
- Speaker: Eibun Senaha, National Central University, Taiwan
- Abstract: We discuss electroweak phase transition (EWPT) in the secluded<br>
U(1)'-extended MSSM with/without CP violation.<br>
Unlike the MSSM, the EWPT can be strong first order without a light stop.<br>
In such a case, the singlet-like Higgs bosons and the charged Higgs bosons<br>
play an important role. It is found that at least two Higgs bosons should be<br>
less than 300 GeV for the strong first order phase transition.<br>
Depending on the charged Higgs boson mass, the lightest Higgs boson can be<br>
as large as 220 GeV. It is also found that the CP violating phase in the Higgs sector<br>
do not weaken the strength of the first order EWPT.<br>
Thursday, April 16th, 2009
- R. G. Herb Condensed Matter Seminar
- Quantum Control and Measurement of Spins in Cold Atomic Gases
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Ivan Deutsch, University of New Mexico
- Abstract: Spins are the natural carriers of quantum information given their long coherence times and the mature methods for controlling them with coherent rf. Spins in atomic gases are of particular interest given their further isolation from a thermal condensed matter environment and our ability to manipulate them optically. Laser cooling and trapping, optical pumping, coherent Raman interactions, and polarization spectroscopy are all tools in the arsenal that can be put to work. In this talk I will review a series of developments in quantum control and measurement of spins in laser-cooled atomic samples, with an eye towards quantum information processing. In collaboration with Poul Jessen, College of Optical Science, University of Arizona, we have designed and implemented tools for arbitrary state preparation in a large-dimensional hyperfine manifold, and quantum-state reconstruction in a single shot based on continuous weak measurement. We have extended this control to the design of arbitrary unitary maps, which will allow qudit logic on large spins. Finally, the coherent interaction between spins is essential for scalable quantum information processing. I will show how one perform quantum logic gates between nuclear spins over tens of nanometers based on optical Feshbach resonances in alkaline-earth-like atoms.
- Host: Mark Saffman
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- High Energy Cosmic Rays with CREAM, Fermi, and Beyond
- Time: 2:00 pm
- Place: 5280 Chamberlin
- Speaker: Terri J. Brandt, Ohio State University
- Abstract: The origins, acceleration mechanism(s), and propagation of high energy cosmic rays within the galaxy have been a mystery for nearly 100 years. Today's experiments are beginning to provide a more complete and definitive answer to these classic questions. I will discuss one such: the Cosmic Ray Energetics And Mass (CREAM) balloon-borne experiment. CREAM uses a complementary set of charge, energy, and tracking detectors on successive balloon flights around the Antarctic continent to directly measure individual CR nuclei's spectra over 5 orders of magnitude in energy. These spectra provide clues to CR origins and acceleration mechanisms. To better understand CR propagation, we have extended the Boron to Carbon ratio over an order of magnitude higher in energy than previous measurements. I will then explore a few ways ongoing and upcoming detections of CR signatures with gamma-ray and neutrino detectors may shed further light on the classic CR questions, both through direct and indirect detection.
- Host: Albrecht Karle
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Quark Matter in Neutron Stars
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Mark Alford, Washington University
- Abstract: Quark matter at high density and low temperature is expected to be a color superconductor, which is a degenerate Fermi gas of quarks with a condensate of Cooper pairs near the Fermi surface. At the highest densities, where the QCD coupling is weak, rigorous calculations are possible, and the ground state is a particularly symmetric state, the color-flavor locked (CFL) phase. At lower densities the CFL phase suffers from flavor-symmetry-breaking stresses, so alternative phases,
some of which break translation and/or rotation invariance, may be favored. I will review the state of our understanding of these phenomena, and discuss the effort to develop signatures of the presence of color superconducting quark matter in neutron stars.
- Host: Michael J. Ramsey-Musolf
Friday, April 17th, 2009
- Theory/Phenomenology Seminar
- Implications of a Scalar Dark Force for Terrestrial Experiments
- Time: 2:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Sonny Mantry, UW-Madison Physics Dept.
- Abstract: Does Dark Matter (DM) fall at a different rate than ordinary matter under gravity? Such a violation of the Weak Equivalence Principle (WEP) could arise
through ultralight scalars mediating a new long range "dark force" between DM particles. Such scenarios can arise, for example, through DM-quintessence
interactions or in non-universal scalar-tensor theories of gravity invoked to explain aspects of dark energy. The presence of a dark force would affect galactic dynamics, the CMB spectrum, and large scale structure formation typically requiring it to be weaker than gravity. Furthermore, a dark force will be communicated to ordinary matter through quantum effects as long as the DM is not sterile. This allows one to further probe dark forces through terrestrial experiments such as Eotvos tests of the WEP, DM-direct-detection experiments, and collider signals. - Physics Department Colloquium
- Neutrino Physics Beyond SNO
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee and cookies at 3:30 pm)
- Speaker: Mark Chen, Queen's University
- Abstract: A follow-up experiment to the Sudbury Neutrino Observatory is being developed, called SNO+. With a liquid scintillator replacing the heavy water, SNO+ will examine neutrino phenomena at lower energies than SNO. Physics goals include: detecting the CNO solar neutrinos and using them to resolve a new puzzle related to solar chemical composition; precision measurements of the survival probability of pep solar neutrinos at the transition energy between vacuum- and matter-dominated oscillation; and measuring the flux of geo-neutrinos in a detector site where the local geology has been extensively characterized, enabling the measurement to address fundamental questions in geoscience. We also plan to add neodymium to the SNO+ liquid scintillator in order to perform a competitive next-generation 0-nu double beta decay search. The physics capabilities and the status of the experiment will be presented.
- Host: Heeger