No abstract

We report a measurement of the mass of the top quark in lepton+jets final states of pp →tt data corresponding to 2.6 fb −1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. A matrix-element method is developed that combines an in situ jet energy calibration with our standard jet energy scale derived from studies of γ+jet and dijet events. We then implement a flavor-dependent jet response correction through a novel approach. This method is used to measure a top-quark mass of mt = 176.01 ± 1.64 GeV. Combining this result with our previous result obtained on an independent data set, we measure a top-quark mass of mt = 174.94 ± 1.49 GeV for a total integrated luminosity of 3.6 fb −1 .

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 dataset corresponding to an integrated luminosity of 5.4 fb −1 , collected by the D0 experiment at the Fermilab Tevatron Collider, we measure the tt 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 decay, found to be (15.2 ± 4.0)%. The results are compared to predictions based on the next-to-leading-order QCD generator mc@nlo. The sensitivity of the measured and predicted asymmetries to the modeling of gluon radiation is discussed.

We combine searches by the CDF and D0 Collaborations for the associated production of a Higgs boson with a W or Z boson and subsequent decay of the Higgs boson to a bottom-antibottom quark pair. The data, originating from Fermilab Tevatron pp collisions at √ s = 1.96 TeV, correspond to integrated luminosities of up to 9.7 fb −1 . The searches are conducted for a Higgs boson with mass in the range 100-150 GeV/c 2 . We observe an excess of events in the data compared with the background predictions, which is most significant in the mass range between 120 and 135 GeV/c 2 . The largest local significance is 3.3 standard deviations, corresponding to a global significance of 3.1 standard deviations. We interpret this as evidence for the presence of a new particle consistent with the standard model Higgs boson, which is produced in association with a weak vector boson and decays to a bottom-antibottom quark pair.

We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2:7-5:4 fb À1 of p p collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f 0 ) and righthanded (f þ ) helicities, we find f 0 ¼ 0:722 AE 0:081½AE0:062ðstatÞ AE 0:052ðsystÞ and f þ ¼ À0:033 AE 0:046½AE0:034ðstatÞ AE 0:031ðsystÞ. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f 0 ¼ 0:682 AE 0:057½AE0:035ðstatÞ AE 0:046ðsystÞ for fixed f þ and f þ ¼ À0:015 AE 0:035½AE0:018ðstatÞ AE 0:030ðsystÞ for fixed f 0 . The results are consistent with standard model expectations.