Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session B4: Research Talks at the Undergraduate Level |
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Sponsoring Units: FEd Chair: David Ehrenstein, APS Room: Hyatt Regency Dallas Marsalis A |
Saturday, April 22, 2006 10:45AM - 11:21AM |
B4.00001: Top Quarks and the High Energy Frontier Invited Speaker: One of the still missing pieces of the Standard Model of particle physics is the Higgs boson, providing a mechanism to generate the masses of the particles. Furthermore, there is strong indication that the Standard Model is merely the low energy limit of a more fundamental theory which could manifest itself near the TeV scale. This talk will explore aspects of experimentation at the High Energy frontier, starting from experience at the Tevatron accelerator currently providing the world's highest energy particle collisions. In particular, a precision measurement of the top quark mass using the Collider Detector at Fermilab (CDF) will be presented. An outlook will be given towards a direct search for the Higgs boson and New Physics at the LHC and beyond, concluding with a historic perspective. [Preview Abstract] |
Saturday, April 22, 2006 11:21AM - 11:57AM |
B4.00002: Ellipsoids beat Spheres: Experiments with Candies, Colloids and Crystals Invited Speaker: How many gumballs fit in the glass sphere of a gumball machine? Scientists have been puzzling over problems like this since the Ancient Greeks. Yet it was only recently proven that the standard way of stacking oranges at a grocery store--with one orange on top of each set of three below--is the densist packing for spheres, with a packing fraction $\phi \quad \sim $ 0.74. Random (amorphous) packings of spheres have a lower density, with $\phi $ $\sim $0.64. The density of crystalline and random packings of atoms is intimately related to the melting transition in matter. We have studied the crystal-liquid transition in spherical colloidal systems on earth and in microgravity. The simplest objects to study after spheres are squashed spheres -- ellipsoids. Surprisingly we find that ellipsoids can randomly pack more densely than spheres, up to $\phi \quad \sim $0.68 - 0.71 for a shape close to that of M{\&}M's$^{\mbox{{\textregistered}} }$Candies, and even approach $\phi \quad \sim $0.75 for general ellipsoids. The higher density relates directly to the higher number of neighbors needed to prevent the more asymetric ellipsoid from rotating. We have also found the ellipsoids can be packed in a crystalline array to a density, $\phi \quad \sim $.7707 which exceeds the highest previous packing. Our findings provide insights into granular materials, rigidity, crystals and glasses, and they may lead to higher quality ceramic materials. [Preview Abstract] |
Saturday, April 22, 2006 11:57AM - 12:33PM |
B4.00003: Why Is the Universe Accelerating? Invited Speaker: Our universe is accelerating, a phenomenon that cannot be accounted for by ordinary matter and conventional gravity. The simplest explanation is to invoke a vacuum energy of 120 orders of magnitude less than the expected amount. Alternatively, there could be a smoothly-distributed, slowly-varying dynamical component, or a breakdown of general relativity on cosmological scales. All of the possibilities are very exciting, and future observations have promise for distinguishing between them. I will give an overview of the theoretical proposals for explaining the acceleration of the universe and the observational constraints which any model must satisfy. [Preview Abstract] |
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