Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session R13: LHC Searches I |
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Sponsoring Units: GPMFC DPF Chair: Nikos Varelas, University of Illinois at Chicago Room: 101 |
Monday, April 7, 2014 10:45AM - 10:57AM |
R13.00001: Search for ttbar resonances in semileptonic final states in pp collisions at $\sqrt{s}$ = 8 TeV Irving Sandoval Gonzalez We present a search for the production of heavy resonances decaying into top-antitop quark pairs at the CMS Experiment. The data correspond to an integrated luminosity of 19.6 fb$^{-1}$ at $ \sqrt{s} = 8$ TeV. We consider all events containing one muon or electron and at least two jets in the final state. We present results from the combination of two dedicated searches, the first optimized for $t\bar{t}$ production at the kinematic production threshold, and the other optimized for $t\bar{t}$ production produced with high Lorentz boosts. We do not observe any excess of events above the expected yield from the standard model processes. We set the following limits at 95$\% $ CL on the production of non-SM particles: topcolor Z' bosons with relative widths of 1.2$\%$ and 10$\%$ are excluded for masses below 2.1 TeV and 2.7 TeV. An upper limit of 1.94 pb and 0.029 pb is set on the production cross section times branching fraction for narrow resonances with masses of 0.5 TeV and 2 TeV. Likewise, limits of 1.71 pb and 0.045 pb are set for wide resonances with masses of 0.5 TeV and 2 TeV. In addition, Kaluza - Klein excitations of a gluon with masses below 2.5 TeV in the Randall - Sundrum model are excluded and an upper limit of 0.101 pb is set for a resonance mass of 2 TeV. [Preview Abstract] |
Monday, April 7, 2014 10:57AM - 11:09AM |
R13.00002: Studying Same Sign $W^{\pm}W^{\pm}$ Production at the LHC Alexander Sood The production of a pair of W bosons with the same electric charge is a process which has not been observed at the LHC. One of its dominant production mechanisms is through the vector boson scattering (VBS), whose unitarization relies on the electroweak symmetry breaking mechanism and makes VBS of great interest to study. This talk, together with the talk by Lulu Liu, will present a measurement of the inclusive same sign $W^{\pm}W^{\pm}$ cross section, as well as a further study of the production through VBS with the requirement that the two leading $p_{\rm T}$ jets are separated by at least 2.4 in rapidity ($\Delta y$). Limits are set on the anomalous quartic gauge couplings (aQGC). The analysis is performed using 20 fb$^{-1}$ of data collected by the ATLAS detector at $\sqrt{s}=$ 8 GeV. This talk will focus on the background estimations. [Preview Abstract] |
Monday, April 7, 2014 11:09AM - 11:21AM |
R13.00003: Same Sign $W^{\pm}W^{\pm}$ Production and Limits on Anomalous Quartic Gauge Couplings Lulu Liu The production of a pair of $W$ bosons with the same electric charge is a process which has not been observed at the LHC. One of its dominant production mechanisms is through the vector boson scattering (VBS), whose unitarization relies on the electroweak symmetry breaking mechanism and makes VBS of great interest to study. This talk, together with the talk by Alex Sood, will present a measurement of the inclusive same sign $W^{\pm}W^{\pm}$ cross section, as well as a further study of the production through VBS with the requirement that the two leading $p_{\rm T}$ jets are separated by at least 2.4 in rapidity ($\Delta y$). Limits are set on the anomalous quartic gauge couplings (aQGC). The analysis is performed using 20 fb$^{-1}$ of data collected by the ATLAS detector at $\sqrt{s}=$ 8 GeV. This talk will focus on the extraction of the cross section and the limits on aQGC. [Preview Abstract] |
Monday, April 7, 2014 11:21AM - 11:33AM |
R13.00004: W' signatures with odd Higgs particles Andrea Peterson, Bogdan Dobrescu We point out that W' bosons may decay predominantly into Higgs particles associated with their broken gauge symmetry. We demonstrate this in a renormalizable model where the W' and W couplings to fermions differ only by an overall normalization. This ``meta-sequential'' W' boson decays into a scalar pair, with the charged one subsequently decaying into a W boson and a neutral scalar. These scalars are odd under a parity of the Higgs sector, which consists of a complex bidoublet and a doublet. The W' and Z' bosons have the same mass and branching fractions into scalars, and may show up at the LHC in final states involving one or two electroweak bosons and missing transverse energy. [Preview Abstract] |
Monday, April 7, 2014 11:33AM - 11:45AM |
R13.00005: A 2-D Sensitivity Study in Searching for a High Mass Z' Boson at $\sqrt{s}$ = 8 TeV with the Dielectron Channel Using the ATLAS Detector Aaron Vermeersch A possible signature of physics beyond the Standard Model could be the observation of an additional neutral, heavy boson such as the Z'. The signal would present itself in the invariant mass spectrum through its decay to dilepton pairs as a resonance on an otherwise irreducible falling background from the Drell-Yan process. Currently at ATLAS, the search for this resonance relies on the invariant mass as the discriminating variable. However, this neglects the potential increase in sensitivity due to the expected angular distributions which stem from the new physics. A sensitivity study was conducted that shows the expected mass limits for two different search scenarios in the high mass region, one using the invariant mass of the dielectron pair and another that is dependent on angular variables, for multiple benchmark Z' models. [Preview Abstract] |
Monday, April 7, 2014 11:45AM - 11:57AM |
R13.00006: Search for W$' \rightarrow$ tb in the hadronic final state in proton-proton collisions at 8 TeV with the ATLAS detector Ho Ling Li We present a model independent search for a $W'$ boson in the $W' \rightarrow t\bar{b} \rightarrow q\bar{q'} b\bar{b}$ final state using $20.3 fb^{-1}$ of 8 TeV data collected by the ATLAS detector from the Large Hadron Collider (LHC) in 2012. This analysis searches for both left- and right-handed chiral $W'$ bosons in the mass range of 1.5 to 3.5 TeV. Reconstructing the hadronically decaying top-quark is done using jet substructure tagging techniques. Limits are set on the ratios of coupling strength $g'$ to the Sequential Standard Model coupling $g_{SM}$. [Preview Abstract] |
Monday, April 7, 2014 11:57AM - 12:09PM |
R13.00007: Search for Z' resonances decaying to top-antitop in dilepton$+$jets final states in pp collisions at 8 TeV center of mass energy Jimin George, Ia Iashvili, Supriya Jain We present a model-independent search for heavy resonances decaying to top-antitop pairs using 19.7/fb of data recorded by the CMS detector in pp collisions at 8 TeV center of mass energy. The search is based on events containing two leptons (electron or muon) and at least two jets. No deviation is observed over the expected rate from the standard model processes. We, therefore, set 95{\%} confidence-level upper limits on the production cross section for the heavy resonances decaying to top-antitop in the mass range of 1-3 TeV. Upper mass limits are set for the narrow and wide width leptophobic top color Z', as well as for the Kaluza-Klein excitation of gluons as predicted in theories beyond the standard model. [Preview Abstract] |
Monday, April 7, 2014 12:09PM - 12:21PM |
R13.00008: A Search for Z'$\to\tau\tau$ using $\sqrt{s}=8$ TeV $pp$ Collisions at ATLAS Andrew Leister Several Standard Model extensions motivated by Grand Unification predict the existence of one or more additional heavy gauge bosons (Z'). The $Z'\to\tau\tau$ analysis at ATLAS uses $\sqrt{s}$ = 8 TeV $pp$ collisions from the Large Hadron Collider to search for such Z' bosons, particularly from models that predict enhanced coupling to third generation particles. The Z' signal in the search is derived from the Sequential Standard Model. In each ditau decay channel a search for an excess over the Standard Model background in high-mass ditau events is performed. In cases where observed events are consistent with the Standard Model background, upper limits are set on the production of high mass resonances. In the most recent public result from the fully hadronic decay channel, heavy mass resonances below 1.9 TeV are excluded at a 95\% confidence level. This result is expected to improve with the inclusion of the other channels. [Preview Abstract] |
Monday, April 7, 2014 12:21PM - 12:33PM |
R13.00009: Search for diboson resonances in the $llqq$ final state using pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector Miles Wu This talk presents a search for $WZ$ and $ZZ$ resonances in the $llqq$ final state, using the ATLAS detector, from pp collisions at $\sqrt{s} = 8$~TeV. Many beyond the Standard Model theories predict heavy vector boson pair resonances. The $llqq$ final state provides a larger branching ratio compared to the fully leptonic state and reduced backgrounds compared to the fully hadronic state. Jet substructure techniques and a new modification to lepton isolation are used to increase sensitivity to high-mass resonances. The bulk Randall-Sundrum graviton and the extended gauge model $W'$ boson are used as benchmark models. [Preview Abstract] |
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