Search results for "Bottom"
showing 10 items of 450 documents
Search for single top quark production inpp¯collisions ats=1.96 TeVin the missing transverse energy plus jets topology
2010
We report a search for single top quark production with the CDF II detector using 2.1 fb{sup -1} of integrated luminosity of pp collisions at {radical}(s)=1.96 TeV. The data selected consist of events characterized by large energy imbalance in the transverse plane and hadronic jets, and no identified electrons and muons, so the sample is enriched in W{yields}{tau}{nu} decays. In order to suppress backgrounds, additional kinematic and topological requirements are imposed through a neural network, and at least one of the jets must be identified as a b quark jet. We measure an excess of signal-like events in agreement with the standard model prediction, but inconsistent with a model without si…
Search for flavor changing neutral currents via quark–gluon couplings in single top quark production using 2.3 fb−1 of pp¯ collisions
2010
We present a search for flavor changing neutral currents via quark-gluon couplings in a sample of single top quark final states corresponding to 2.3 fb(-1) of integrated luminosity collected with the DO detector at the Fermilab Tevatron Collider. We select events containing a single top quark candidates with an additional jet, and obtain separation between signal and background using Bayesian neural networks. We find consistency between background expectation and observed data, and set limits on flavor changing neutral current gluon couplings of the top quark to up quarks (tgu) and charm quarks (tgc). The cross section limits at the 95% C.L. are sigma(tgu) gu) gc) < 3.9 x 10(-3).
Light Quark Yukawa Couplings and the W ± h Charge Asymmetry
2017
Abstract I review the recent theory progress on possibly measuring the light quark couplings, emphasizing the distinction between direct and indirect measurements. I highlight the importance of the W ± h charge asymmetry measurement as a direct probe of enhanced light quark Yukawa couplings. I propose the W ± h → l ± l ± q q ′ ν ν final state as a promising channel for measuring the charge asymmetry. This clean, same-sign dilepton final state should reach statistical discovery sensitivity in each W ± h charge mode with 300 fb -1 of Large Hadron Collider luminosity, and affords an impressive sub-percent statistical accuracy with the anticipated 3 ab -1 high luminosity upgrade. After accounti…
Search for W′→tb resonances with left- and right-handed couplings to fermions
2011
We present a search for the production of a heavy gauge boson, W', that decays to third-generation quarks, by the D0 Collaboration in ppbar collisions at sqrt(s)= 1.96 TeV. We set 95% confidence level upper limits on the production cross section times branching fraction. For the first time, we set limits for arbitrary combinations of left- and right-handed couplings of the W' boson to fermions. For couplings with the same strength as the standard model W boson, we set the following limits for M(W') > m(nu_R): M(W')>863 GeV for purely left-handed couplings, M(W')>885 GeV for purely right-handed couplings, and M(W')>916 GeV if both left- and right-handed couplings are present. The limit for r…
Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at s=7 TeV with t…
2013
A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb(-1) of pp collisions root s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton + jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t'(t') over bar signal when m(t') greater than or similar to 400 GeV. No significant excess of events above t…
Search for admixture of scalar top quarks in the tt¯ lepton + jets final state at s=1.96 TeV
2009
A search for pair production of the lightest supersymmetric partner of the top quark is performed in the lepton+jets channel using 0.9 fb-1 of data collected by the D0 experiment. Kinematic differences between scalar top quark pair production and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.
Nucleon Structure Functions in a Constituent Quark Scenario
1999
Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the polarized part on distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized as well as in the polarized case, though a good description of the recent polarized neutron data requires the introduction of one more paramater. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present scheme is impressive. We conclude that DIS data are consistent with a low energy scenario dominat…
O(alpha_s) Spin-Spin Correlations for Top and Bottom Quark Production in e+ e- Annihilation
1997
We present the full O(alpha_s) longitudinal spin-spin correlations for heavy-quark pair production at e+ e- high-energy colliders in closed analytical form. In such reactions, quark and antiquark have strongly correlated spins, and the longitudinal components are dominant. For the explicit computation of the QCD bremsstrahlung contributions, new phase-space integrals are derived. Explicit numerical estimates are given for t t_bar and b b_bar production. Around the Z-peak, QCD one-loop corrections depolarize the spin-spin asymmetry for bottom quark pairs by approximately -4%. For top pair production, we find at 350GeV a 0.6% increased polarization over a value of 0.4 in the longitudinal corr…
The running of the b-quark mass from LEP data
1997
Next-to-leading order QCD corrections to three jet heavy quark production in $e^+ e^-$ collisions, including quark mass effects, are presented. The extraction of the b-quark mass form LEP data is considered and the first experimental evidence for the running of a quark mass is discussed.
126 GeV Higgs boson in the top-seesaw model
2013
We consider a model of dynamical electroweak symmetry breaking built on the idea of top-seesaw mechanism. The model features a fourth generation of vector-like QCD quarks responsible for the origin of the top-seesaw mechanism and leading to the natural explanation of the large splitting between the top and bottom quark masses. Motivated by the LHC data on the couplings of the Higgs boson, we include the entire third generation of Standard Model matter fields into the model. We determine the low energy effective theory and the resulting low energy spectrum of states, and constrain the model parameters with constraints from the precision electroweak data and from the requirement of a light sc…