Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session X11: Top and Flavor |
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Sponsoring Units: DPF Chair: Joe Incandela, University of California, Santa Barbara Room: Roosevelt 3 |
Tuesday, January 31, 2017 10:45AM - 10:57AM |
X11.00001: Limits on anomalous contributions to the Wtb vertex Christopher Pease, Miguel Fiolhais, Antonio Onofre Recent LHC results on the measurements of the W-boson helicity fractions and single top quark production cross section at a center-of-mass energy of 13 TeV are combined in order to establish new limits on anomalous contributions to the Wtb vertex. The allowed regions for these limits are presented in three-dimensional graphics, for both real and imaginary components of the different anomalous couplings, allowing all the other anomalous couplings to vary at the same time. These results are combined with the prospected future measurement of the single top quark production cross section and W-boson helicity fractions at the LHC. When compared with the previous most precise limits, these results show a significant improvement, larger than 10\%. [Preview Abstract] |
Tuesday, January 31, 2017 10:57AM - 11:09AM |
X11.00002: A measurement of jet substructure variables in prompt J/\psi events with the ATLAS detector at $\sqrt{s}=$ 8 TeV David Bjergaard, Ayana Arce There are many open questions regarding charmonium production at hadron colliders. In order to describe the $p_T$ spectrum of prompt J/$\psi$ particles, the color octet mechanism from non-relativistic QCD (NRQCD) must be introduced. Color octet states have a net color charge which is expected to enhance hadronic activity around the J/$\psi$. Recently it has been suggested that jet substructure techniques may be able to discriminate between the the octet and singlet production mechanisms. Simulations of of N-subjettiness and the J/$\psi$-jet momentum fraction indicate the ability to separate the two production mechanisms. This work presents the first measurement of these variables (N-subjettiness, $\Delta R$ and jet-momentum fraction $z$) in $pp$ collisions at $\sqrt{s}=8~\text{TeV}$ with the ATLAS detector. [Preview Abstract] |
Tuesday, January 31, 2017 11:09AM - 11:21AM |
X11.00003: A Template Measurement of the Top Quark Angular Distribution Using Boosted Lepton + Jets Events Nick Eminizer We present a template-based technique for measuring the angular distribution of top quark pairs decaying semileptonically using data collected by the CMS experiment at the LHC. The analysis is optimized for high-momentum ``boosted'' decays wherein the hadronically decaying top quark's jets become either partially or fully merged, and the final state lepton is not necessarily isolated from nearby jets. The technique can be used to examine multiple physics processes affecting the angular distribution of top pairs, including the parton-level top quark forward-backward asymmetry $A_{FB}$ and anomalous chromoelectric/chromomagnetic moments. [Preview Abstract] |
Tuesday, January 31, 2017 11:21AM - 11:33AM |
X11.00004: Factorial Moments and Intermittency in pp Collisions at $\sqrt{s}$ = 13 TeV Khadeejah ALGhadeer Charged-particle multiplicity dependence on transverse momentum, pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are presented for pp collisions at center of mass energy $\sqrt{s} = 13$ TeV with two different Monte Carlo event generators, Pythia 8 and Herwig++ 2.7.1, including studies of ${t}$ ${t}'$ production. The results are achieved with charged particles with transverse momentum larger than 500 MeV and absolute pseudorapidity less than 3, in events with at least one charged particle, and in events at least six charged particles filling these kinematic requirements. In this paper, intermittency studys the distributions of particles and correlations of multiplicities of charged particles in one-dimensional phase space of rapidity is presented to analyze the dynamics of hadroproduction. Intermittency is an increase of factorial moments with decreasing bin size, where dynamical fluctuations are noticed. The dynamical correlations of many-particle systems are carried out at higher energies, where one cannot separate out lower-order correlations from higher-order correlations. The behavior of particle distributions call intermittent provide a strong test of QCD. [Preview Abstract] |
Tuesday, January 31, 2017 11:33AM - 11:45AM |
X11.00005: Probing the CP nature of Higgs couplings in tth events at the LHC Miguel Fiolhais, Christopher Pease, Antonio Onofre The CP nature of the Higgs coupling to top quarks (tth) is studied in proton-proton collision events at a centre-of-mass energy of 13 TeV at the LHC. Pure scalar and pseudo-scalar Higgs boson signal events are generated with MadGraph5\_aMC@NLO, and analysed in dileptonic final states with two oppositely charged leptons and four jets. These events are fully reconstructed by applying a kinematic fit. As a result, new angular distributions of the decay products as well as CP angular asymmetries are explored to separate the scalar from the pseudo-scalar components of the Higgs boson, which allows to reduce the contribution from the dominant irreducible background, ttbb. In addition, significant differences between the angular distributions and asymmetries are observed, providing new observables for a global fit of the Higgs couplings parameters. [Preview Abstract] |
Tuesday, January 31, 2017 11:45AM - 11:57AM |
X11.00006: Status of the KOTO experiment at J-PARC Brian Beckford The K0TO experiment conducted at J-PARC was designed to observe the K$^{0}_{L} \rightarrow \pi^{0}\nu\bar{\nu}$ decay and measure its branching ratio. The current SM prediction for the branching ratio is 3.0 x 10$^{-11}$ with a small theoretical uncertainty of about 2-3%. Studying this rare decay is an ideal candidate to search for physics beyond the standard model. The previous search performed by the KEK E391a collaboration set a limit on the branching ratio of 2.6 x 10$^{-8}$. As a result of the favorable outcome of KEK E391, the K0TO experiment is intended to pursue the search with increased beam power, an upgraded data acquisition system, and improved detector hardware. The signature of the decay is a pair of photons from the $\pi^{0}$ decay and no other detected particles. For the measurement of the energies and positions of the photons, K0TO uses a Cesium Iodide (CSI) electromagnetic calorimeter as the main detector, and hermetic veto counters to guarantee that there are no other detected particles. The initial data was collected in 2013, followed by additional runs in 2015-2016 at beam powers of 24 and 40 kW, respectively. In this talk, we present a description of the upgrades and improvements to the detector, present status, and the latest results. [Preview Abstract] |
Tuesday, January 31, 2017 11:57AM - 12:09PM |
X11.00007: $\mu \to e$ Conversion in the Electroweak-scale Right-handed Neutrino Model Trinh Le, P.Q. Hung, Van Que Tran, T.C. Yuan Within the framework of the Electroweak-scale right-handed neutrino (EW-$\nu_R$) model, we calculate the rate for $\mu \to e$ conversion with a particular aim at the sensitivities of the upcoming experiments, Mu2e ($6 \times 10^{-17}$) and COMET ($3 \times 10^{-17}$). Our calculations show a direct relationship between the rate for $\mu \to e$ conversion and that for $\mu \rightarrow e \gamma$. Upon comparing the projected sensitivities with the present limit from SINDRUM II ($6.1 \times 10^{-13}$) and including the upper bound on $\mu \rightarrow e \gamma$ ($5.7 \times 10^{-13}$), we found that approximately only half of the allowed parameter space between the SINDRUM II limit and the sensitivities of Mu2e and COMET is available ($\sim 10^{-17} - 10^{-15}$). [Preview Abstract] |
Tuesday, January 31, 2017 12:09PM - 12:21PM |
X11.00008: ABSTRACT WITHDRAWN |
Tuesday, January 31, 2017 12:21PM - 12:33PM |
X11.00009: Measuring the $t\bar{t}$ forward-backward asymmetry using semileptonic final states at 8 TeV with the CMS detector Lei Feng, Nick Eminizer, Morris Swartz This talk presents a measurement of forward-backward asymmetry in $t\bar{t}$ production. The data sample corresponds to $19.7\,\textrm{fb}^{-1}$ of integrated luminosity in proton--proton collisions at $\sqrt{s} = 8\,\textrm{TeV}$ collected by the CMS experiment at the LHC. Events selected contain a single isolated muon or electron, with four or five jets of which two are b-tagged. A template technique is used to extract the asymmetry from the difference in the top quark kinematic distribution relative to the boost direction of the $t\bar{t}$ center of mass system. This technique is based upon a linear extension of the tree-level cross section for $q\bar{q}$ initial states and it sensitively isolates those initial states from $gg/qg$ initial states. The quantity produced by this technique is already corrected to parton level and is directly comparable to similar quantities derived from the Tevatron measurements. [Preview Abstract] |
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