Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session J9: Top Quark |
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Sponsoring Units: DPF Chair: Robert Kehoe, Southern Methodist University Room: Embassy E |
Sunday, April 1, 2012 1:30PM - 1:42PM |
J9.00001: Simultaneous cross-section measurements of SM $e\mu$ final state processes at ATLAS Kevin Finelli We present a method for the simultaneous extraction of Standard Model (SM) processes using the $e\mu$ dilepton final state. In a 2-D phase space defined by missing transverse energy and jet multiplicity the main SM contributions of $t\bar{t}$, $WW$, and $Z \rightarrow \tau\tau$ are well separated. After selecting $e\mu$ events, and making no further requirements on the events, we fit the data to templates of the three aforementioned processes, the normalizations of which are allowed to float, and smaller contributions which are constrained to their uncertainties. The result of the likelihood fit provides the simultaneous measurement of the $t\bar{t}$, $WW$, and $Z \rightarrow \tau\tau$ cross-sections, as well as providing a more global test of the SM as compared to a more conventional cross-section measurement. We present results from $5 fb^{-1}$ of data collected by the ATLAS detector. [Preview Abstract] |
Sunday, April 1, 2012 1:42PM - 1:54PM |
J9.00002: Measurement of the cross section in $t\bar t$ + jets using a multivariate kinematics fit method with the ATLAS detector Babak Abi A measurement of the production cross-section for $t\bar t$ events with an additional jet ($t\bar t$ + jet) is presented, using 5.0 fb$^{-1}$ of data collected by the ATLAS detector at $\sqrt{s} =7$ TeV at the LHC in 2011. The measurement is performed in the semileptonic decay channel ( $t\bar t \rightarrow \ell\nu b\,bjj$) with electrons or muons in the final state. A multivariate kinematic approach is used in order to extract the background events, a 2D likelihood is formed to simultaneously measure the $t\bar t$ + jet and inclusive $t\bar t$ cross-sections. [Preview Abstract] |
Sunday, April 1, 2012 1:54PM - 2:06PM |
J9.00003: Precision measurement of the top quark mass in events with two leptons at D0 Huanzhao Liu We present a measurement of the top quark mass in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV using $t\bar{t}$ events with two leptons ($ee$, $e\mu$ or $\mu\mu$) in the final state. This analysis utilizes an integrated luminosity of 4.3 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron collider. We employ a neutrino weighting technique to extract the top mass from 319 dilepton events. To reduce the dominant systematic uncertainties from jet energy calibration, we apply the jet energy corrections determined from a dijet invariant mass using $W\to jj$ decays in $t\bar{t}\to\ell +$jets events. We also apply corrections to jets in Monte Carlo events to replicate the flavor dependence of the jet response in data. [Preview Abstract] |
Sunday, April 1, 2012 2:06PM - 2:18PM |
J9.00004: W Helicity measurement in top quark events with D0 Amitabha Das We report on a model-independent measurement of the helicity of W bosons produced in top quark decays based on a 5.4/fb sample of top quark pair events, collected by the D0 detector at Fermilab, colliding protons and anti-protons at the center of mass energy of 1.96 TeV, in the dilepton and lepton+jets channels. In the standard model, the fraction of longitudinal (right-handed) W bosons is predicted to be 0.7 (0). The deviation from these values would be a clear sign of new physics. [Preview Abstract] |
Sunday, April 1, 2012 2:18PM - 2:30PM |
J9.00005: Search for Violation of Lorentz Invariance in $t\overline{t}$ Production and Decay at the D0 Experiment Denver Whittington Data used in the analysis of the $t\overline{t}$ production cross section in the lepton + jets channel is examined as a function of sidereal time. According to the standard model extension (SME), any sidereal time dependence in the yield would reflect the violation of Lorentz Invariance in the top quark sector. Within the SME framework, we set upper limits on the XX, XY, XZ, YY, and YZ components of the coefficients $(c_Q)_{\mu\nu 33}$ and $(c_U)_{\mu\nu 33}$ used to parametrize violation of Lorentz invariance in the top quark sector. [Preview Abstract] |
Sunday, April 1, 2012 2:30PM - 2:42PM |
J9.00006: Diagnosing the top-quark angular asymmetry using LHC intrinsic charge asymmetries Simon Knapen, Yue Zhao, Matthew Strassler Flavor-violating interactions involving new heavy particles are among proposed explanations for the $t\bar t$ forward-backward asymmetry observed at the Tevatron. Many of these models generate a $t\bar t$-plus-jet signal at the LHC. In this paper we identify several new charge asymmetric variables in $t\bar tj$ events that can contribute to the discovery of such models at the LHC. We propose a data-driven method for the background, largely eliminating the need for a Monte Carlo prediction of $t\bar t$-plus-jets, and thus reducing systematic errors. With a fast detector simulation, we estimate the statistical sensitivity of our variables for one of these models, finding that charge-asymmetric variables could materially assist in the exclusion of the Standard Model across much of the mass and coupling range, given 5 inverse fb of data. Should any signal appear, our variables will be useful in distinguishing classes of models from one another. [Preview Abstract] |
Sunday, April 1, 2012 2:42PM - 2:54PM |
J9.00007: Measurements of single top quark production cross section and search for anomalous $Wtb$ Couplings at D0 Jyoti Joshi We present new measurements of the single top quark production cross section in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV using data corresponding to 5.4 fb$^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider. The large mass of the top quark, close to the electroweak symmetry-breaking scale, makes it a good candidate for probing physics beyond the Standard Model, e.g. anomalous couplings. We examine the data to study the Lorentz structure of the $Wtb$ coupling. We find that the data prefer the left-handed vector coupling and set upper limits on the anomalous couplings. [Preview Abstract] |
Sunday, April 1, 2012 2:54PM - 3:06PM |
J9.00008: NLO QED Contributions to Top Quark Pair Production Jia Zhou, Andreas Scharf, Doreen Wackeroth Top quark pairs are produced via quark-antiquark annihilation $q\bar{q}\rightarrow t\bar{t}$ and gluon-gluon fusion $gg\rightarrow t\bar{t}$ and decay rapidly through electroweak interaction $t\rightarrow Wb$ with a branching fraction of 99\% in the Standard Model(SM). That the measured forward-backward asymmetry of top-pair production at the Tevatron deviates from that predicted in the SM is intriguing in view of searching for the presence of possible new physics. We here consider ${\cal O} (\alpha_s^2\alpha)$ contributions in the QED sector to top-pair production. Results are given for the observable hadronic cross section at the Tevatron and the LHC. [Preview Abstract] |
Sunday, April 1, 2012 3:06PM - 3:18PM |
J9.00009: ABSTRACT WITHDRAWN |
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