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This Week at Physics

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Events on Monday, March 26th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The search for direct detection of Dark Matter with MiniCLEAN
Time: 1:00 pm
Place: 4274 Chamberlin Hall
Speaker: Raul Hennings-Yeomans, Los Alamos National Laboratory
Abstract: The particle nature of dark matter remains one of the biggest challenges in Astroparticle physics today. The use of liquid noble elements as scintillators for direct detection of dark matter insingle and dual phase configurations are one of the most promising techniques to reach sensitivities beyond 10$^{-44}$cm$^2$ in spin-independent WIMP-nucleon cross section. MiniCLEAN (CLEAN- Cryogenic Low Energy Astrophysics with Noble Gases) is an approximately spherical ~500~kg liquid argon or neon vessel that encloses 92 optical cassettes (modular photo-detectors) pointing at the center of the sphere through a TPB (Tetraphenyl Butadine) evaporated window that converts VUV light from the argon or neon scintillation into the visible. The modular spherical design allows both for a viable radon-mitigated assembly and for position reconstruction. Furthermore, the use of Pulse-Shape discrimination techniques between nuclear and electronic recoils that are particularly good for these two condensed noble gases will test the single-phase approach as a viable instrument for direct detection of dark matter at the multi-tonne scale with a projected sensitivity of 10$^{-46}$~cm$^2$ for a $sim$100~GeV/c$^2$ WIMP mass in terms of spin-independent WIMP-nucleon cross section. I will be presenting a review and status of the MiniCLEAN research program as well as new developments in the mitigation of depth-dependent and radiogenic neutron backgrounds.
Host: Reina Maruyama
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Condensed Matter Theory Group Seminar
Superconducting Instabilities in Cuprates Mediated by Spin Density Wave Order at Quantum Criticality
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Yuxuan Wang, UW-Madison
Abstract: I will start with the introduction of the model and its uniqueness near quantum criticality, especially, its distinction with BCS-type theories. I will use a solved example in a specific temperature scale to show how in this case perturbation theory fails to account for the critical temperature of the system. Next I will demonstrate that in another temperature scale the superconducting vertex shows a log2 (Λ/T) behavior up to leading contributions, which would seem to give Tc ~ exp (−1/√g), g being the coupling. I will then present how this problem again cannot be properly addressed by counting leading contributions in each order of perturbation theory. Theoretical and numerical investigations are then used to show the actual exp (−1/g) behavior of the critical temperature. Finally by looking at the full problem, I will talk about the conditions at which each temperature scale takes dominance, and what one can learn from studying the models at these specific temperature scales.
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