Bulletin of the American Physical Society
2007 Joint Fall Meeting of the Texas Sections of the APS and AAPT; Zone 13 of SPS
Volume 52, Number 16
Thursday–Saturday, October 18–20, 2007; College Station, Texas
Session B3: HEN1: High Energy/Nuclear |
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Chair: Robert Webb, Texas A&M University Room: Rudder Tower 701 |
Friday, October 19, 2007 10:40AM - 10:52AM |
B3.00001: Comparing Methods for Multivariate Classifier Training Variable Selection using the Search for the Scalar Top Quark as a Case Study. Dennis Mackin We look for a way to automate the process of training variable selection when applying multivariate event classifiers to the search for new phenomenon in high energy physics experiments. The D{\O} collaboration recently completed a search for the Supersymmetric partner of the top quark in the two muons, two jets, and missing transverse energy final state. We use the Monte Carlo events representing the signal and the background from this search as the basis for our case study. We begin with the computationally expensive, $\mathcal{O}$($2^n$), method of testing the classifier for all variable combinations and then selecting the one combination which gives the best expected signal sensitivity. We then compare this ``best'' sensitivity to the sensitivities of the classifier when trained using variable combinations suggested by less expensive methods such as sequential forward selection, chi-squared and K-S testing, and physicist intuition. Even in this age of grid computing, the total number of variables which can be tested is limited. In our case, we were limited to considering eleven variables. A less expensive method of variable selection would not only free up computing resources, it would enable us to consider a much larger set of variables for use in the multivariate classifier. [Preview Abstract] |
Friday, October 19, 2007 10:52AM - 11:04AM |
B3.00002: Searches for a Dark Matter Candidate in Particle Physics Experiments at the Fermilab Tevatron Paul Geffert, Max Goncharov, Eunsin Lee, Rishi Patel, David Toback, Peter Wagner, Vyacheslav Krutelyov Astronomical observations have shown that the amount of visible matter in the universe comprises only a fraction of the total mass of the current universe. Models of Supersymmetry can account for this mass by predicting new particles. We present a search for these particles in proton anti-proton collisions at the Fermilab Tevatron using a new timing device on the Collider Detector at Fermilab and discuss prospects for future searches into the cosmologically favored region of parameter space for models with heavy, long-lived neutralinos that decay into photons and gravitinos. [Preview Abstract] |
Friday, October 19, 2007 11:04AM - 11:16AM |
B3.00003: Probing 23{\%} of the Universe at the Large Hadron Collider Alfredo Gurrola, Richard Arnowitt, Bhaskar Dutta, Teruki Kamon, Abram Krislock, Dave Toback With recent astronomical measurements, we know that 23{\%} of the Universe is accounted by a mysterious dark matter. The results have constrained the parameter space of supersymmtery (SUSY), which is a leading theory that could connect cosmology and particle physics and offers an explanation of the dark matter. A characteristic prediction from the parameter space is that the supersymmetric tau lepton and the lightest neutralino are nearly mass degenerate (mass difference of $\sim $ 5-15 GeV) and can be created at the Large Hadron Collider (LHC). We present a methodology to extracting the dark matter signals at the LHC, and show the accuracy to which we can measure the dark matter relic density and the SUSY parameters. [Preview Abstract] |
Friday, October 19, 2007 11:16AM - 11:28AM |
B3.00004: Dark Matter Relic Density and Supersymmetry at the LHC Jonathan Asaadi The theory of Supersymmetry (SUSY) could provide a fundamental link between early Big Bang cosmology and particle physics by providing a possible explanation to the origin and abundances of the Dark Matter. WMAP measurements, in addition to other experimental results, help constrain the SUSY parameter space to a region known as the co-annihilation region where the stau and the neutralino (LSP) are nearly the same mass (mass difference $\sim$ 5-15GeV). We present one approach to extracting information about the Dark Matter candidate at the LHC in addition to the different parameters of the minimal Supergravity (mSUGRA) model of SUSY. [Preview Abstract] |
Friday, October 19, 2007 11:28AM - 11:40AM |
B3.00005: Heavy-Quark diffusion in the Quark-Gluon Plasma Hendrik van Hees, Massimo Mannarelli, Vincenzo Greco, Ralf Rapp The Quark-Gluon Plasma (QGP) is a hot and dense state of matter predicted by Quantum Chromo Dynamics (QCD) to exist at temperatures above T~200MeV ($\sim 10^{12}$~Kelvin). The QGP is believed to have prevailed in the first few microseconds after the big bang. Experiments at the Relativistic Heavy Ion Collider (RHIC) are trying to recreate, for a short moment, the QGP in the laboratory. It has been found that the matter produced in high-energy Au-Au collisions is a strongly coupled quark-gluon liquid with very low viscosity and high opacity. To understand the properties of this strongly coupled QGP (sQGP) heavy quarks (charm and bottom) are a particularly valuable probe: they are produced early in the reaction and subsequently diffuse in the putative sQGP. In this talk we develop a model for nonperturbative interactions between heavy and light quarks in the sQGP and apply it to experimental spectra at RHIC. Good agreement with data allows for a quantitative estimate of the heavy-quark diffusion coefficient in the sQGP. [Preview Abstract] |
Friday, October 19, 2007 11:40AM - 11:52AM |
B3.00006: Transverse-momentum dependence of $J/\psi$ suppression in heavy-ion collisions Xingbo Zhao, Ralf Rapp A central goal of heavy-ion collisions at high energies is the production of the Quark-Gluon Plasma (QGP), a new state of matter in which quarks and gluons are deconfined. A promising signature of deconfinement in these collsions may be a suppression of $J/\psi$ particles, due to the Debye screening of the strong force in the QGP. However, recent theoretical developments suggest that $J/\psi$ mesons can be regenerated via recombination of charm and anti-charm quarks in the QGP. To disentangle these mechanisms, we perform a systematic study of $J/\psi$-formation processes and investigate $J/\psi$ transverse-momentum distributions in heavy-ion collisions at different energies (at the SPS at CERN and at the Relativistic Heavy-Ion Collider at Brookhaven). We employ a two-component model to compare $J/\psi$ $p_t$ distributions to experimental data. [Preview Abstract] |
Friday, October 19, 2007 11:52AM - 12:04PM |
B3.00007: Systematic Statistical Study of NAHE Based String Models Tim Renner, Jared Greenwald, Gerald Cleaver We are conducting a systematic study of the phenomenological properties of models on the region of the string landscape occupied by weak coupled heterotic strings in the free fermionic formalism. Specifically, we are examining the statistics of phenomenological properties, including of the superpotential, of the collection of models formed as extensions of the Nanopoulos, Antoniadis, Hagelin, and Ellis (NAHE) set of free fermionic basis vectors. The NAHE he observable gauge group is SO(10) with N=1 supersymmetry. We systematically generate all possible sets of free fermionic basis vector extensions to the NAHE set that reduce the SO(10) model to Flipped SU(5) models, Left-Right Symmetric (Pati-Salam-like) models, and MSSM-like models. (Several of such models have been constructed and studied individually by various research groups in the past.) All possible order-2 through order-4 basis vector extensions consistent with SO(10) breaking and modular invariance were constructed as part of a 2007 REU summer project with graduate students at Baylor University. Systematic generation and statistics collection of the related models has begun. Generation of additional higher order basis vector extensions is in process. [Preview Abstract] |
Friday, October 19, 2007 12:04PM - 12:16PM |
B3.00008: Heterotic Strings on Mirror Half-Flat Manifolds Tibra Ali, Gerald Cleaver In this talk we report on progress made in the study of $E_8 \times E_8$ heterotic string theory on mirror half-flat manifolds. We are motivated to study this system because mirror half-flat manifolds offer a way to fix some of the moduli of heterotic string theory on Calabi-Yau manifolds. We argue that the analogue of standard embedding in the half-flat case is to embed the natural torsionful connection into the gauge connection. The surviving subgroup is still $E_6 \times E_8$ as in Calabi-Yau compactification. We show this by thinking of the heterotic string on a half-flat manifold as a ``reduction" of $R^{1,2}\times Z_7$, where $Z_7$ is non-compact $G_2$ holonomy cylinder foliated by compact mirror half-flat leaves. We then report progress on working out the effective action of heterotic string theory on these manifolds. [Preview Abstract] |
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