Bulletin of the American Physical Society
10th Annual Meeting of the Northwest Section of APS
Volume 53, Number 6
Thursday–Saturday, May 15–17, 2008; Portland, Oregon
Session G4: Particle Physics |
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Chair: Janis McKenna, University of British Columbia Room: Miller 102 |
Saturday, May 17, 2008 2:00PM - 2:12PM |
G4.00001: Determining the Muon Mass in an Instructional Laboratory Christopher May, Benjamin Brau, John Essick An instructional laboratory experiment to measure the muon mass $m_{\mu}c^2$ is described. Using coincidence-anticoincidence detection, the decay of a cosmic-ray muon into an electron (or positron) is observed in a multiplate spark chamber, and recorded with a triggered CCD detector. The energy $E_e$ of the charged decay-product particle is then determined by the number of chamber plates it traverses before being stopped. By running this apparatus under computer-control for several hours, the number distribution $N(E_e)$ of product-particles with energy $E_e$ is obtained. Based on the quantum electrodynamics analysis of muon decay, the muon mass can then be obtained either from the largest observed value for $E_e (=m_\mu c^2/2)$, the average energy of the distribution $(=7m_\mu c^2/20)$, or fitting $N(E_e)$ to the predicted functional form of $E_e ^2(1-4E_e/3m_\mu c^2)$. We present the results for $m_{\mu}c^2$ obtained from our apparatus by these three approaches and discuss the simulation we have developed to account for the observed skewing of $N(E_e)$ due to escape of some of the higher-energy product particles from the chamber. [Preview Abstract] |
Saturday, May 17, 2008 2:12PM - 2:24PM |
G4.00002: Nanometer Vibration Control by Computer Feedback Kevin McLeod, Steven Schramm, Janis McKenna, Thomas Mattison The International Linear Collider is a planned electron-positron accelerator at the 500 GeV scale. Colliding nanometer sized beams requires control of vibrations of the final focusing magnets at the nanometer level. We are investigating position measurement with laser interferometry and position control with piezoelectric actuators using state-vector feedback in a near-real-time Linux computing environment. A custom driver for a commercial ADC-DAC card has the interferometer reconstruction and feedback algorithms inside an interrupt handler running at 10 kHz. Linux user applications interact with the driver for interferometer alignment and calibration, measurement of excitation of internal modes by the piezo, and measurement of external vibration spectrum. Other applications analyze the internal and external vibration modes, and calculate state-vector feedback gains. Graphical interface is provided by tcl/tk. Code development is in C with standard GNU tools, using a recursive generic makefile. [Preview Abstract] |
Saturday, May 17, 2008 2:24PM - 2:36PM |
G4.00003: Nanometer Vibration Analysis for Future Linear Colliders Steven Schramm, Kevin McLeod, Janis McKenna, Thomas Mattison Future linear electron-positron colliders require nanometer beam sizes for adequate luminosity, so mechanical vibrations at the nanometer level are a critical issue. One approach is measuring component (or accelerometer test-mass) positions with laser interferometry, which has sub-nanometer resolution. The position information is then input to a state-vector control algorithm for use in adjusting component positions, steering the beam, or simply as diagnostic information. Fourier analysis of our test interferometer data shows dominant contributions from many relatively narrow peaks, plus frequency-dependent broadband noise. We have developed automated methods of analyzing such data to produce the information required for the state-vector algorithm to predict future motion and also to control it. [Preview Abstract] |
Saturday, May 17, 2008 2:36PM - 3:12PM |
G4.00004: LHC Physics with the ATLAS Detector Invited Speaker: The Large Hadron Collider will be the highest energy accelerator in the world when it begins operation later this year. The LHC will allow us to probe many of the current issues in particle physics such as the origin of mass, the identity of dark matter and how many dimensions the universe has. An introduction to ATLAS, one of the LHC experiments, will be given, along with prospects for physics measurements in the near future. [Preview Abstract] |
Saturday, May 17, 2008 3:12PM - 3:24PM |
G4.00005: An investigation of observable signatures in ATLAS from LSP decays to the Hidden Valley Jacob Miner We present an ongoing investigation into the observable signatures from the Hidden Valley* model in the ATLAS detector at the Large Hadron Collider. Other recent studies have investigated decays to the Hidden Valley from a Z' or Higgs, however, this study investigates decays through the neutral LSP in supersymmetric scenarios. The neutral Hidden Valley particles may have long lifetimes and thus produce unique challenges in detecting their decays. Using a modified Pythia card created by M. Strassler, we show that the triggers proposed in the Z' and Higgs studies will assist in detecting the LSP decay to Hidden Valley pions. \newline \newline *M. Strassler and K. Zurek, Physics Letters B 651 (2007) 374--379; Physics Letters B, 661 (4), p.263-267 [Preview Abstract] |
Saturday, May 17, 2008 3:24PM - 3:36PM |
G4.00006: Topological vector currents and neutron star kicks James Charbonneau We propose that the asymmetry required to create neutron star kicks with large magnitudes, $v>800km/s$, is carried by non-dissipating currents that travel along the superconducting vortices in the neutron star. These currents, called topological vector currents, appear specifically in systems with non-zero magnetic flux and an asymmetry in the number of left and right-handed fermions. A satisfying explanation for large kicks does not yet exist. Two candidates are hydrodynamic instabilities and asymmetric neutrino flux. With hydrodynamic kicks an asymmetric mass distribution triggers an asymmetric explosion during formation but it is not clear that enough momentum is produced. Neutrino kicks involve neutrino transport caused by the magnetic field and the weak interaction, but the required momentum is generated at temperatures high enough that detailed balance washes out the asymmetry. Kicks from topological currents are powered by the electron chemical potential, not the temperature, so are not washed out and the momentum carried by these currents appears to be capable of generating the large velocities observed in some neutron stars. [Preview Abstract] |
Saturday, May 17, 2008 3:36PM - 3:50PM |
G4.00007: BREAK
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Saturday, May 17, 2008 3:50PM - 4:02PM |
G4.00008: Visualizing Non-Asymptotic Quantum Scattering from a Separable Potential Jared Stenson, Albert Stetz Quantum scattering processes are often only investigated in the asymptotic limit. However, using a separable gaussian potential we present analytic scattering solutions, which are valid even non-asymptotically. We use MATLAB visualizations of this non-asymptotic region to show the interference that occurs near the scatterer. Extending the visualizations using Bohm's quantum trajectories and more complicated scattering potentials will also be discussed. [Preview Abstract] |
Saturday, May 17, 2008 4:02PM - 4:14PM |
G4.00009: Classification of Hadron Bound States Carl Brannen Consider a system where a small number of valence fermions interact with each other through an unspecified potential. As usual, a complete set of commuting operators define a set of bound states that are orthonormal. We work with density matrices so that a complete basis set of bound states are primitive idempotents that annihilate each other. That is, $\rho_n\rho_m = \rho_n\delta_{nm}$ and $tr(\rho) = 1$. As an example, we use the bound states of the hydrogen atom. In order to model deeply bound particles, we suppose that the continuous degrees of freedom for the wave functions is reduced to a small finite number. We analyze the structure of complete basis sets of primitive idempotent NxN complex matrices for N=2 and N=3. For the baryons, we assume that the three colors of the valence quarks give N=3 and conclude that their resonances will appear in groups of three with the same quantum numbers, for example, $\{\Delta(1232), \Delta(1600), \Delta(1920)\}$ each of which is $P_{33}$. We discuss applications of the theory to classifying the mesons. We discuss Koide's mass formulas for the leptons and extensions to formulas for triples of hadrons. [Preview Abstract] |
Saturday, May 17, 2008 4:14PM - 4:26PM |
G4.00010: Parity, Time Reversal, and Relativity Robert Close Derivation of the conventional Dirac operators for spatial inversion ($P)$ and time reversal ($T)$ assumes that the squared coefficients of the temporal and spatial derivatives are elements of the Minkowski metric. The validity of this assumption is questionable since each component of the free-particle Dirac equation satisfies the Klein-Gordon equation which, while Lorentz invariant, can be used to describe waves propagating in classical Galilean space-time. The conventional parity operator also violates the rules of geometric algebra for certain vector-like sets of matrices representing alternative velocity representations. Taking the coefficient of temporal derivatives to be unity as in Dirac's original formulation, the resultant operators for spatial inversion and time reversal are found to be consistent with geometric algebra. The new parity operator exchanges matter and anti-matter and is therefore consistent with spatial reflection symmetry (instantaneous parity conservation) for all known physical processes. The combined \textit{PT} and \textit{PCT} operators are unchanged by the new definitions. [Preview Abstract] |
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