Bulletin of the American Physical Society
11th Annual Meeting of the Northwest Section of APS
Volume 54, Number 6
Thursday–Saturday, May 14–16, 2009; Vancouver, BC, Canada
Session G3: Particle Physics |
Hide Abstracts |
Chair: Stanley Yen, TRIUMF Room: Hennings 202 |
Saturday, May 16, 2009 1:30PM - 2:06PM |
G3.00001: Giant loops in hot SYM and holography Invited Speaker: The AdS/CFT correspondence is a powerful tool which can be used, among other things, to explore the strong coupling behaviour of ${\cal N}=4$ super Yang-Mills theory with large number of colors. In this work, we look for phase transitions in hot SYM on a spacial three-sphere. In particular, we study the expectation value of the Polyakov loop operator in large completely symmetric and completely antisymmetric representations. A non-zero expectation value for the loop signals that the corresponding representation is confined. We find, for example, that in the deconfined phase of SYM, large enough symmetric representations are confined, while smaller representations are not. This represents a phase transition. On the gravity side of the AdS-CFT duality, the related Maldacena-Wilson loop corresponds to a fundamental string worldsheet suspended into the bulk of AdS from the loop contour at the boundary. When the representation is large, the fundamental string wraps the contour many times, and undergoes a `blow up' to a higher dimensional object, a D-brane. Finite temperature requires a black hole horizon at the center of AdS, and the question of confinement at non-zero temperature translates to asking whether or not the D-brane touches the horizon. [Preview Abstract] |
Saturday, May 16, 2009 2:06PM - 2:18PM |
G3.00002: Relativistic non-instantaneous action-at-a-distance interactions Domingo Louis-Martinez Relativistic action-at-a-distance theories with interactions that propagate at the speed of light in vacuum are investigated. We consider the most general action depending on the velocities and relative positions of the particles. The Poincare invariant parameters that label successive events along the world lines can be identified with the proper times of the particles provided that certain conditions are imposed on the interaction terms in the action. Further conditions on the interaction terms arise from the requirement that mass be a scalar. A generic class of theories with interactions that satisfy these conditions is found. The relativistic equations of motion for these theories are presented. We obtain exact circular orbits solutions of the relativistic one-body problem. The exact relativistic one-body Hamiltonian is also derived. The theory has three components: a linearly rising potential, a Coulomb-like interaction and a dynamical component to the Poincare invariant mass. At the quantum level we obtain the generalized Klein-Gordon-Fock equation and the Dirac equation. [Preview Abstract] |
Saturday, May 16, 2009 2:18PM - 2:30PM |
G3.00003: The Cosmological Dark Energy as a Standard Model Effect Evan Thomas, Federico Urban, Ariel Zhitnitsky We propose that the Dark Energy (cosmological constant) could be, in fact, a Standard Model effect which requires no new physics. We look to the infrared sector of the effective QFT of gravity and the conformal anomaly as a source for a non-clustered, homogeneous, and isotropic energy density. In this talk I will introduce our field theoretic definition for the cosmological constant, together with our proposed renormalization subtraction procedure. I will then present some preliminary results and discuss any phase transition which alters the quantum ground state as a possible source for non-zero contributions to our cosmological constant. [Preview Abstract] |
Saturday, May 16, 2009 2:30PM - 2:42PM |
G3.00004: Quarks, Leptons, and Density Matrices Carl Brannen For an operator to be a pure density matrix it is necessary and sufficient that it be Hermitian, have trace one, and it be a projection operator. These are commonly generalized by giving up the projection operator requirement; the result are mixed density matrices convenient for modeling statistical mixtures. Other generalizations are also interesting. We solve for the Hermitian projection operators of a simple algebra based on the permutations of three elements, and show that the solutions give the weak quantum numbers, $(t_0,t_3)$, of the quarks and leptons. [Preview Abstract] |
Saturday, May 16, 2009 2:42PM - 2:54PM |
G3.00005: Statistics of energy losses of fast electrons Hans Bichsel Electrons deflected by the field of a nucleus will emit photons
(``Bremsstrahlung, BMS"), resulting in energy losses $E$.
The differential cross section for this effect is of the form
$\sigma_b(E)=\chi/E$. For Si, $\chi \sim~2\cdot
10^{-24}$~cm$^2$/nucleus.
For collisions with atomic electrons the differential cross
section is
$\sigma_R(E,\beta)=\xi/E^2$, $\xi=1.3\cdot 10^{-19}$~eV/cm$^2$ for
fast electrons ($\beta=v/c\sim1$).
We use the {\it moments }
$M_0(T) \equiv N \int_{E_l}^{T} \sigma_{\mathrm{rad}} (E;T) dE $
to get the mean number of collisions per cm and
$M_1(T) \equiv N \int E~ \sigma_{\mathrm{rad}} (E;T) dE $
to get the mean energy loss per cm for electrons with energy
$T$, giving $_b M_0(T)=\chi~\ln (T/E_l)$ and
$_R M_0(T)=\xi~ (1/T~-~1/E_l)$. Also
$_bM_1(T)~=~\chi \cdot T$, $_R M_1(T)=\xi~\ln (T/E_l)$.
Assuming $E_l=20$ eV,
$M_0$ depends little on $T$, and the {\it average energy loss per
collision} $ |
Saturday, May 16, 2009 2:54PM - 3:06PM |
G3.00006: HALO -- Helium And Lead Observatory for Supernova Neutrinos Stanley Yen Existing neutrino detectors are primarily sensitive to electron anti-neutrinos via charged-current interactions on hydrogen nuclei. The large neutron excess of a heavy nucleus like Pb makes it primarily sensitive to electron neutrinos. This channel is expected to show the most interesting effects of flavor-swapping and spectral splitting due to MSW-like collective neutrino-neutrino interactions in the core of the supernova, the only place in the universe where there is a sufficient density of neutrinos for this to occur. The observation of a galactic core-collapse supernova by a Pb-based neutrino detector, as a complement to other neutrino detectors, would provide a wealth of data for both particle physicists and astrophysicists. The data would provide a test for $\theta_{13 }\ne$ 0 and an inverted neutrino mass hierarchy, and measure the temperature of the cooling neutron star. HALO is a detector now under construction in SNOLAB, which will utilize 80 tons of surplus Pb blocks, together with the neutral-current detectors from the SNO experiment and the SNO data acquisition system, to provide a low-cost, low-maintenance, long-lived, high-livetime detector. [Preview Abstract] |
Saturday, May 16, 2009 3:06PM - 3:26PM |
G3.00007: BREAK
|
Saturday, May 16, 2009 3:26PM - 4:02PM |
G3.00008: What we can expect from the first year of the LHC Invited Speaker: The ATLAS and CMS experiments at the CERN Large Hadron Collider have been built and commissioned over more than a decade. They are the most complex experiments ever assembled, but were completed in time for the first beams in the LHC in September 2008. The accident which interrupted the LHC startup did not interrupt the commissioning of the detectors with cosmic ray events, and the small amount of single-beam data collected in September was invaluable for timing in the detector. ATLAS and CMS will therefore be unusually well calibrated and understood by the time collision data become available in Fall 2009. The first part of the talk will discuss the expected performance of the detectors (with some bias towards ATLAS). The rest of the talk will discuss physics analyses which should be possible with the first year's running at the LHC. Roughly 100-200~pb$^{-1}$ at a 10~TeV centre-of-mass energy are needed to match the Tevatron's Standard Model Higgs sensitivity around 160~GeV - if all goes according to plan, the LHC may collect this by Fall 2010. About 100~pb$^{-1}$ at 10~TeV would match the full Tevatron sample of top quarks; roughly twice as much data would be needed if the run were mainly at 8~TeV. Sensitivity to $W'$ or $Z'$ resonances would match the Tevatron's with less than 100~pb$^{-1}$ at 8~TeV. Prospects for discovering supersymmetry are even more promising: in some models as little as 10~pb$^{-1}$ at 8~TeV could yield a 5~$\sigma$ discovery. The next year is expected to be a critical period in defining the future of high energy physics, as the actual performance of the LHC and its detectors is tested with collision data. Discoveries of physics beyond the Standard Model could potentially be made by the end of the first year's running, especially if the start-up progresses smoothly. [Preview Abstract] |
Saturday, May 16, 2009 4:02PM - 4:14PM |
G3.00009: Upgrade of the $\beta\!-\!\nu$ correlation experiment with beta decay of optically trapped $\rm^{38m}$K atoms Alexandre Gorelov, John Behr, Peter Jackson, Matt Pearson, Danny Ashery, Dan Melconian TRIUMF's $\beta\!-\!\nu$ correlation measurements from beta decay of optically trapped $\rm^{38m}$K atoms resulted in the world best limit on the presence of general scalar interaction in superallowed $0^+\!\rightarrow 0^+$ Fermi decays (PRL {\bf 94},142501,2005). Observing trapped atoms by $\Delta E-E$ scintillator based beta-telescope and MCP based recoil detector in back-to-back geometry, we were able to deduce $\beta\!-\!\nu$ correlations. Analysis of the systematics has shown that the main limitations come from characterisation of the beta-detector, applied electric field and knowlege of energy dependent probability of the recoil ionization. A new improved setup utilyzing larger experimental chamber and detectors and stronger, better characterized applied electric field should allow us to significantly reduce systematic errors and reach 0.1\% resulting error. [Preview Abstract] |
Saturday, May 16, 2009 4:14PM - 4:26PM |
G3.00010: Searching for exotic particle emission in the decay of trapped Rb isomers Tao Kong, Alexander Gorelov, Tegan Wiebe, Matthew Pearson, John Behr During the decay of nuclear isomers, the momentum of the recoil nucleus will change if any massive particle is emitted instead of a Gamma photon. The Rb isomer transitions are sensitive to a mass range between 20 to 550 keV/c$_{2}$. This range covers masses for pseudoscalar axions which were proposed to solve the strong CP problem and for scalar particles. In our experiment, trapped metastable Rb isomers will be used to search for these particles. To measure the recoiling momentum, the daughter Rb atoms are photo-ionized. The resulting electrons and photo-ions are detected in a ``MOTRIMS'' setup, where charged particles are guided onto time and position sensitive detectors by means of electric fields. The photo-ionization involves firstly the excitation from 5S state to 5D state by Doppler-free two-photon transitions using an MBR-110 laser at 778 nm, and then ionization to the continuum by a broadband Fibre laser at 1064 nm. [Preview Abstract] |
Saturday, May 16, 2009 4:26PM - 4:38PM |
G3.00011: High precision measurement of the $\pi \rightarrow e \nu$ branching ratio: a sensitive probe in the search for new physics Kaoru Yamada Study of rare decays is an important approach for exploring physics beyond the Standard Model (SM). New physics could be seen if deviations from well-calculated SM predictions occur. In particular, the branching ratio of the helicity suppressed pion decays, $\frac{\Gamma(\pi\rightarrow e \nu_e + \pi\rightarrow e \nu_e \gamma)}{\Gamma(\pi\rightarrow\mu \nu_\mu+\pi\rightarrow\mu\nu_\mu\gamma)}$ is the most accurately calculated decay process involving hadrons and has so far provided the most stringent test of the hypothesis of electron-muon universality in weak interactions. It has been calculated in the SM to better than 0.01\% to be $\textrm{R}_{SM}=1.2353(1)\times10^4$. The PIENU experiment at TRIUMF, which will be online in a few weeks, aims to reach an accuracy five times better than the current world average value so as to confront the theoretical calculation at the level of $\pm$0.1\%. At this level,``new physics'' beyond the Standard Model, at potentially very high mass scales, could be revealed or sensitive constraints on hypotheses can be obtained for interactions involving pseudoscalar, axial vector, or scalars The presentation will outline the physics motivations behind the measurement and describe the PIENU experiment's concept, apparatus and techniques designed to achieve the high precision measurement of the branching ratio. [Preview Abstract] |
Saturday, May 16, 2009 4:38PM - 4:50PM |
G3.00012: High Purity Beam in the TRIUMF M13 CHANNEL Chloe Malbrunot The branching ratio of pion decays $\frac{\Gamma(\pi\rightarrow e \nu_e + \pi\rightarrow e \nu_e \gamma)}{\Gamma(\pi\rightarrow\mu \nu_\mu+\pi\rightarrow\mu\nu_\mu\gamma)}$, has provided the best test of the hypothesis of electron-muon universality in weak interactions. The new PIENU experiment at TRIUMF, aiming to improve the precision of the branching ratio measurement by a factor $>5$, measures positrons from the two-body decay $\pi^{+}\rightarrow e^{+}\nu_e$ $(E_{e^+}=69.8\textrm{MeV})$ and the $\pi^{+}\rightarrow\mu^{+} \rightarrow e^{+}$ $(E_{e^+}\leq52.8 \textrm{MeV})$ chain. In order to achieve large acceptance, the detector system including a large NaI(Tl) calorimeter is placed on the beam axis. Since this detector configuration is very sensitive to positron contamination in the beam, the TRIUMF low energy pion channel, M13, has been upgraded to reduce by a factor of 100 the number of positrons in the beam (which was 1/3 of the number of pions before upgrade). This presentation will describe the suppression technique based on energy-loss as well as the simulation and test results which confirm that the performance of the upgraded beamline satisfies the requirements of the PiENu experiment. The presentation will also outline the measurement of $\pi^{+}\rightarrow e^{+}\nu_e$ decays from the beamline which constitute a source of 100 \% polarized positron and provides a new beam channel momentum calibration source. [Preview Abstract] |
Saturday, May 16, 2009 4:50PM - 5:02PM |
G3.00013: Photonuclear effects in a NaI(Tl) calorimeter Luca Doria The branching ratio $R=\Gamma (\pi\rightarrow e\nu+e\nu\gamma)/ \Gamma (\pi\rightarrow \mu\nu + \mu\nu\gamma)$ has provided the best test of the hypothesis of electron-muon universality in weak interactions. The new TRIUMF PIENU experiment aims at improving the precision of this measurement by a factor of $>5$. A key component of the experiment is a NaI(Tl) calorimeter for positron energy measurements. During test measurements, additional peak structures were observed in the positron spectra. Using Monte Carlo simulation, we show that these structures are due to photonuclear reactions. [Preview Abstract] |
Saturday, May 16, 2009 5:02PM - 5:14PM |
G3.00014: Muon decay asymmetry and the standard model James Bueno The asymmetry of the positron in polarised muon decay provides confirmation that the weak interaction maximally violates parity. Since 1957, the quantity $P_\mu \xi$ has been measured with increasing precision, where $P_\mu$ is the polarisation of the muon, and $\xi$ is a parameter describing the asymmetry. So far, the results have been consistent with the standard model's $(V-A)$ interaction. The TRIUMF Weak Interaction Symmetry Test (TWIST) is close to completing a measurement of $P_\mu \xi$ at the level of $0.1\%$. An order of magnitude improvement over pre-TWIST results is anticipated. The experiment uses highly polarised muons from pion decay, and is limited in precision by a knowledge of how much the muons depolarise before decaying. At this level, the experiment is sensitive to physics beyond the standard model, such as the weak decay of right-handed muons, and left-right symmetric models where a $(V+A)$ current is introduced to conserve parity at higher energies. The physics motivation and experiment will be described, including the methods that have reduced the dominant systematic uncertainties. [Preview Abstract] |
Saturday, May 16, 2009 5:14PM - 5:26PM |
G3.00015: Design and Performance of Liquid Xenon Detectors for PET Astrid Muennich, Pierre Amaudruz, Douglas Bryman, Leonid Kurchaninov, Philip Lu, Cam Marshall, Jean Pierre Martin, Fabrice Retiere, Aleksey Sher This work is aimed at developing liquid xenon (LXe) detectors for applications to positron emission tomography (PET). The advantages of LXe for PET compared to currently used methods include improved energy resolution by combining information from measuring the ionization as well as the scintillation light, 3-D sub-mm spatial resolution, and Compton scattering reconstruction. Results obtained for the energy resolution with a small prototype and an analysis of error sources will be presented. [Preview Abstract] |
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