Bulletin of the American Physical Society
14th Annual Meeting of the Northwest Section of the APS
Volume 57, Number 7
Thursday–Saturday, October 18–20, 2012; Vancouver, British Columbia, Canada
Session H3: Particle Physics II |
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Chair: Gordon Watts, University of Washington Room: SFU Harbour Centre 2270 Sauder Industries Policy Room |
Saturday, October 20, 2012 1:30PM - 2:06PM |
H3.00001: Searches for New Physics at the Energy Frontier Invited Speaker: Bernd Stelzer CERN's Large Hadron Collider (LHC) is recently performing at record luminosities and energies that enables a program systematically addressing some of the most fundamental questions of nature. On July 4th, 2012 the ATLAS and CMS experiments at the LHC announced observation of a new particle one that is consistent with the legendary Higgs boson, linked to the question of origin of mass. Both collaborations, ATLAS and CMS, have since analyzed datasets up to 11/fb that push searches for new physics to higher and higher sensitivity. I will present a summary of the latest Higgs results and highlight some of the key searches for Physics beyond the Standard Model of particle physics. [Preview Abstract] |
Saturday, October 20, 2012 2:06PM - 2:18PM |
H3.00002: Search for Resonances Decaying into Top Quark Pairs Using Fully Hadronic Decays in $pp$ Collisions with ATLAS at $\sqrt{s}$ = 7 TeV Stephen Swedish A search for a new top quark pair resonance at the CERN Large Hadron Collider with the ATLAS detector is performed on 4.66 fb$^{-1}$ of data collected at $\sqrt{s}$ = 7 TeV. The search uses a new method for tagging jets that correspond to highly energetic top quark decays that tests the agreement of calorimetric energy depositions with the three-prong top quark decay hypothesis. The top quark plays an important role in many theories of physics beyond the Standard Model which often predict the existence of a new massive boson that couples dominantly to top quarks. The search reveals no evidence of a new top quark pair resonance, and the result is used to exclude Kaluza-Klein gluons as predicted by the Randall-Sundrum model with masses between 1.02 and 1.62 TeV, and to set cross-section limits on the leptophobic Z' boson. [Preview Abstract] |
Saturday, October 20, 2012 2:18PM - 2:30PM |
H3.00003: Search for high-mass resonances decaying to lepton pairs with the ATLAS detector Simon Viel We present a search for high-mass $\ell^{+}\ell^{-}$ resonances in $pp$ collisions at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment in 2011. No statistically significant excess above the Standard Model expectation is observed in a dataset corresponding to an integrated luminosity of approximately 5 fb$^{-1}$. Consequently, upper limits are set on the cross-section times branching ratio of resonances decaying to muon pairs as a function of the resonance mass. In particular, a Sequential Standard Model $Z'$ is excluded for masses below 2.22 TeV, and a Randall-Sundrum Kaluza-Klein graviton with coupling $k/\overline{M}_{Pl} = 0.1$ is excluded for masses below 2.16 TeV, both at the 95\%~C.L. Results using data recorded by the ATLAS experiment in 2012 at a centre-of-mass energy of 8 TeV will also be presented. [Preview Abstract] |
Saturday, October 20, 2012 2:30PM - 2:42PM |
H3.00004: Search for supersymmetry in final states with three leptons and missing transverse momentum in $\sqrt{s}$ = 7 TeV $pp$ collisions with the ATLAS detector Sam King A search for the direct production of weak gauginos in final states with three leptons and missing transverse momentum is presented. An integrated luminosity of 4.7 fb$^{-1}$ of $\sqrt{s}$ = 7 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector has been analyzed. Consistency with Standard Model expectations was observed in three signal regions that are either depleted or enriched in $Z$-boson decays. Upper limits at 95$\%$ confidence level have been set in the parameter spaces of the phenomenological minimal supersymmetric Standard Model and simplified models. [Preview Abstract] |
Saturday, October 20, 2012 2:42PM - 2:54PM |
H3.00005: Determination of the Jet Energy Scale at ATLAS using Z+Jet Events Jamie Horton, Mike Vetterli A correct energy calibration for jets is essential to the success of the ATLAS experiment. In this talk the missing transverse energy projection fraction method, an in-situ jet energy calibration currently being being used in the ATLAS detector will be discussed. In particular preliminary results using this method in events where a Z-boson balances a jet in transverse momentum will be shown. The response derived from these events can be used to complement a response derived in gamma-jet events for low transverse momentum, as well as a method for separating the responses for jet initiated by quarks and gluons. These quark and gluon responses will allow for a selection specific jet energy calibration to be derived for individual physics analysis based on the composition of the jets being observed. [Preview Abstract] |
Saturday, October 20, 2012 2:54PM - 3:06PM |
H3.00006: Exploring the CP nature of the Higgs within the context of the Type III Two Higgs Doublet Model Peter Winslow, Sean Tulin We investigate the possibility that the newly discovered boson at the LHC belongs to a set of new bosons originating in a general type III two Higgs doublet model. New sources of CP violation from the scalar potential which mix the electrically neutral scalar and pseudo-scalar states lead to the Higgs acquiring a pseudo-scalar admixture. This mixing is tightly constrained by electric dipole moments, electroweak oblique parameters, and vacuum stability. However, within a small region of parameter space, a sizeable pseudo-scalar admixture cannot be excluded and allows for a large enhancement in the Higgs to di-photon signal rate. We discuss how the LHC Higgs data can provide complementary information in constraining the CP nature of the Higgs boson. [Preview Abstract] |
Saturday, October 20, 2012 3:06PM - 3:26PM |
H3.00007: BREAK |
Saturday, October 20, 2012 3:26PM - 3:38PM |
H3.00008: Bring the Higgs to Rest Jacobus van Nieuwkoop In the Standard Model of Physics, the Higgs boson can decay to a pair of W bosons which decay leptonically. At ATLAS, we have developed a discriminator that classifies events as signal-like or background-like based on their kinematics. This discriminator requires the calculation of the matrix element (derived from Feynman rules) for both signal and background hypotheses. One assumption that we made is that the Higgs is at rest in the transverse plane of the detector. However, this is often not the case due to next-to-leading order effects like initial state radiation. In order to improve our sensitivity we attempt to boost the Higgs into its transverse rest frame. Since the neutrinos pass through ATLAS undetected, we do not have direct access to the Higgs 4-momenta. My talk will describe how we used multivariate techniques to estimate the transverse momentum of the Higgs. [Preview Abstract] |
Saturday, October 20, 2012 3:38PM - 3:50PM |
H3.00009: Search for a light Higgs Boson at Babar Rocky So Babar collided electrons and positrons at a centre of mass energy of 10GeV at the Stanford Linear Accelerator Center. A light CP-odd Higgs boson is expected in extensions to the Standard Model such as Next to Minimal Supersymmetry. The Babar Collaboration searched for a light Higgs boson (A0) produced in radiative decays of an Y meson. We saw no evidence of the A0 decaying into various final states with a sample of 122 million Y(3S), 99 million Y(2S), and 23 million Y(1S) collected at the PEP II B-factory. We exclude some of the parameters space of Next to Minimal Supersymmetry. Some searches are published and a few is still in the analysis stage. I will present work done by the collaboration as well as my work in progress for the A0 to hadrons. [Preview Abstract] |
Saturday, October 20, 2012 3:50PM - 4:02PM |
H3.00010: The Topological Casimir Effect Moos van Caspel, Charles Cao, Ariel Zhitnitsky The conventional Casimir effect manifests itself as a quantum-mechanical force between two plates, that arises from the quantization of the electromagnetic field in the enclosed vacuum. In this talk the possibility is discussed of an extra, topological term in the Casimir energy at finite temperatures. This topological Casimir effect emerges due to the nontrivial topological features of the gauge theory and becomes apparent when examining, for example, periodic boundary conditions. Here the extra term is explicitly calculated for the simplest example of such a system: two large plates in the x-y plane, with an integer-valued topological flux in the z-direction. By dimensional reduction, this system is closely related to 2D Maxwell theory, which is well understood. We find that the topological term is extremely small compared to the conventional Casimir energy, but that the effect could possibly be amplified by an external magnetic field. [Preview Abstract] |
Saturday, October 20, 2012 4:02PM - 4:14PM |
H3.00011: Physical Implications of Topological Casimir Effect ChunJun Cao, Moos Van Caspel, Ariel Zhitnitsky Casimir effect is typically known as the presence of an attractive force between two neutrally charged and perfectly conducting parallel plates in vacuum. It was known that an extra term in the Casimir energy emerges from non-trivial topological features of the gauge fields, but this effect is greatly suppressed in the typical setup of Casimir effect experiments. Nevertheless, I will show in this presentation that in the presence of a non-zero external magnetic field, this topological effect is greatly enhanced, making it possible to be measured in experiments. [Preview Abstract] |
Saturday, October 20, 2012 4:14PM - 4:26PM |
H3.00012: Long range order in gauge theories: Deformed QCD as a toy model Evan Thomas I present some recent work (arXiv:1208.2030) on long range order in gauge theories, using a ``deformed'' QCD model. I first introduce the theory and the formulation of topological objects, mainly monopoles and domain walls. I then present our numerical calculation and results related to the interaction between a monopole and a nearby domain wall. Finally, I discuss how this can help us understand some recent lattice QCD results which indicate that topological charge in real QCD may be exclusively spread along extended objects rather than localized in point-like instantons. [Preview Abstract] |
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