Search results for "Top Quark"
showing 10 items of 266 documents
Top quark mass measurement in the lepton plus jets channel using a modified matrix element method
2008
We report a measurement of the top quark mass, m(t), obtained from p(p)over bar collisions at root s=1.96 TeV at the Fermilab Tevatron using the CDF II detector. We analyze a sample corresponding to an integrated luminosity of 1.9 fb(-1). We select events with an electron or muon, large missing transverse energy, and exactly four high-energy jets in the central region of the detector, at least one of which is tagged as coming from a b quark. We calculate a signal likelihood using a matrix element integration method, where the matrix element is modified by using effective propagators to take into account assumptions on event kinematics. Our event likelihood is a function of m(t) and a parame…
Measurement of the cross section for top-quark pair production in pp collisions at √s = 7TeV with the ATLAS detector using final states with two high…
2012
A measurement is reported of the production cross section of top-quark pairs (tt¯) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. Candidate events have a signature consistent with containing two isolated leptons, large missing transverse momentum, and at least two jets. Using a data sample corresponding to an integrated luminosity of 0.70 fb−1, a tt¯ production cross section σtt¯=176±5(stat.)+14−11(syst.)±8(lum.) pb is measured for an assumed top-quark mass of mt = 172.5 GeV. This measurement is in good agreement with Standard Model predictions.
Search for charged Higgs bosons through the violation of lepton universality in t(t)over-bar events using pp collision data at root s=7 TeV with the …
2013
In several extensions of the Standard Model, the top quark can decay into a bottom quark and a light charged Higgs boson H [superscript +], t → bH [superscript +], in addition to the Standard Model decay t → bW. Since W bosons decay to the three lepton generations equally, while H [superscript +] may predominantly decay into τν, charged Higgs bosons can be searched for using the violation of lepton universality in top quark decays. The analysis in this paper is based on 4.6 fb[superscript −1] of proton-proton collision data at √s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider. Signatures containing leptons (e or μ) and/or a hadronically decaying τ (τ [subscript had])…
W polarisation beyond helicity fractions in top quark decays
2010
30 páginas, 14 figuras, 1 tabla.-- arXiv:1005.5382v2
Forward-backward asymmetry in top quark-antiquark production
2011
Made available in DSpace on 2022-04-29T02:17:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-12 We present a measurement of forward-backward asymmetry in top quark-antiquark production in proton-antiproton collisions in the final state containing a lepton and at least four jets. Using a data set corresponding to an integrated luminosity of 5.4fb -1, collected by the D0 experiment at the Fermilab Tevatron Collider, we measure the tt̄ forward-backward asymmetry to be (9.2±3.7)% at the reconstruction level. When corrected for detector acceptance and resolution, the asymmetry is found to be (19.6±6.5)%. We also measure a corrected asymmetry based on the lepton from a top quark deca…
Search for right-handed W bosons in top quark decay
2005
We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This …
Search for charged Higgs bosons in top quark decays
2009
We present a search for charged Higgs bosons in top quark decays. We analyze the \eplus, \muplus, $ee$, $e\mu$, $\mu\mu$, \etau and \mutau final states from top quark pair production events, using data from about 1${\text{fb}}^{-1}$ of integrated luminosity recorded by the \dzero experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a $\tau$ lepton and a $\tau$ neutrino and a third one where both decays appear. We extract limits on the branching ratio $B(t\to H^+ b)$ for all these models. We use two method…
Heavy quark impact factor and the single bottom production at the LHC
2014
Grigorios Chachamis Instituto de Fisica Corpuscular, Universitat de Valencia – Consejo Superior de Investigaciones Cientificas, Parc Cientific, E-46980 Paterna (Valencia), Spain E-mail: grigorios.chachamis@ific.uv.es Michal Deak∗ Instituto de Fisica Corpuscular, Universitat de Valencia – Consejo Superior de Investigaciones Cientificas, Parc Cientific, E-46980 Paterna (Valencia), Spain E-mail: michal.deak@ific.uv.es
10.7 Weak quark mixing and the CKM matrix
2008
Analytical results forO(αs)radiative corrections toe+e−→tt¯↑up to a given gluon energy cut
2009
We determine the O({alpha}{sub s}) radiative corrections to polarized top quark pair production in e{sup +}e{sup -} annihilations with a specified gluon energy cut. We write down fully analytical results for the unpolarized and polarized O({alpha}{sub s}) cross sections e{sup +}e{sup -}{yields}tt(G) and e{sup +}e{sup -}{yields}tt{sup {up_arrow}}(G) including their polar orientation dependence relative to the beam direction. In the soft-gluon limit we recover the usual factorizing form known from the soft-gluon approximation. In the limit when the gluon energy cut takes its maximum value we recover the totally inclusive unpolarized and polarized cross sections calculated previously. We provi…