Search for Resonant WW and WZ Production in pp collisions at √s=1.96 TeV

We search for resonant WW or WZ production by using up to 5.4 fb(-1) of integrated luminosity collected by the D0 experiment in run II of the Fermilab Tevatron Collider. The data are consistent with the standard model background expectation, and we set limits on a resonance mass by using the sequential standard model W' boson and the Randall-Sundrum model graviton G as benchmarks. We exclude a sequential standard model W' boson in the mass range 180-690 GeV and a Randall-Sundrum graviton in the range 300-754 GeV at 95% C.L.

Bounds on an anomalous dijet resonance in W+jets production in pp collisions at √s = 1.96 TeV

We present a study of the dijet invariant mass spectrum in events with two jets produced in association with a W boson in data corresponding to an integrated luminosity of 4.3 fb(-1) collected with the D0 detector at √s = 1.96 TeV. We find no evidence for anomalous resonant dijet production and derive upper limits on the production cross section of an anomalous dijet resonance recently reported by the CDF Collaboration, investigating the range of dijet invariant mass from 110 to 170 GeV/c(2). The probability of the D0 data being consistent with the presence of a dijet resonance with 4 pb production cross section at 145 GeV/c(2) is 8×10(-6).

Search for diphoton events with large missing transverse energy in 6.3 fb(-1) of pp collisions at √s=1.96 TeV

We report a search for diphoton events with large missing transverse energy produced in pp collisions at √s=1.96  TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider and correspond to 6.3  fb(-1) of integrated luminosity. The observed missing transverse energy distribution is well described by the standard model prediction, and 95% C.L. limits are derived on two realizations of theories beyond the standard model. In a gauge-mediated supersymmetry breaking scenario, the breaking scale Λ is excluded for Λ<124  TeV. In a universal extra dimension model including gravitational decays, the compactification radius R(c) is excluded for R(c)(-1)<477  GeV.

Search for new fermions ("quirks") at the Fermilab Tevatron collider

We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in 2.4 fb⁻¹ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron pp collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like SU(N) sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107, 119, and 133 GeV for the mass of a charged quirk with strong dynamics scale Λ in the range from 10 keV to 1 MeV and N=2, 3, and 5, respectively.

Search for events with leptonic jets and missing transverse energy in pp collisions at √s=1.96 TeV

We present the first search for pair production of isolated jets of charged leptons in association with a large imbalance in transverse energy in pp collisions using 5.8 fb⁻¹ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider. No excess is observed above the standard model background, and the result is used to set upper limits on the production cross section of pairs of supersymmetric chargino and neutralino particles as a function of "dark-photon" mass, where the dark photon is produced in the decay of the lightest supersymmetric particle.

Evidence for an anomalous like-sign dimuon charge asymmetry

We measure the charge asymmetry A ≡ (N++ - N--)/(N++ + N--) of like-sign dimuon events in 6.1 fb-1 of pp collisions recorded with the D0 detector at a center-of-mass energy square root(s) = 1.96   TeV at the Fermilab Tevatron collider. From A we extract the like-sign dimuon charge asymmetry in semileptonic b-hadron decays: A(sl)(b) = -0.009 57 ± 0.002 51(stat) ± 0.001 46(sys). It differs by 3.2 standard deviations from the standard model prediction A(sl)(b)(SM) = (-2.3(-0.6)(+0.5)) × 10(-4), and provides first evidence of anomalous CP violation in the mixing of neutral B mesons.

Search for the standard model higgs Boson in the ZH-->nunubb channel in 5.2 fb{-1} of pp collisions at sqrt[s]=1.96 TeV

A search is performed for the standard model Higgs boson in 5.2 fb{-1} of pp collisions at sqrt[s]=1.96 TeV, collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered is a pair of b jets and large missing transverse energy, as expected from pp-->ZH-->nunubb production. The search is also sensitive to the WH-->lnubb channel when the charged lepton is not identified. For a Higgs boson mass of 115 GeV, a limit is set at the 95% C.L. on the cross section multiplied by branching fraction for [pp-->(Z/W)H](H-->bb) that is a factor of 3.7 larger than the standard model value, consistent with the factor of 4.6 expected.

Measurement of the W boson mass

We present a measurement of the W boson mass in W-->e(nu) decays using 1 fb-1 of data collected with the D0 detector during Run II of the Fermilab Tevatron collider. With a sample of 499830 W-->e(nu) candidate events, we measure M(W)=80.401+/-0.043 GeV. This is the most precise measurement from a single experiment.

Direct measurement of the mass difference between top and antitop quarks

We present a measurement of the mass difference between t and t[over] quarks in lepton + jets final states of tt[over] events in 1 fb;{-1} of data collected with the D0 detector from Fermilab Tevatron Collider pp[over] collisions at sqrt[s] = 1.96 TeV. The measured mass difference of 3.8 +/- 3.7 GeV is consistent with the equality of t and t[over ] masses. This is the first direct measurement of a mass difference between a quark and its antiquark partner.

Search for resonant pair production of neutral long-lived particles decaying to bb in pp collisions at square root(S)=1.96 TeV

We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a bb pair, using 3.6 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.

Search for next-to-minimal supersymmetric Higgs bosons in the h --> aa --> micromicromicromicro, micromicrotautau channels using pp[over] collisions at sqrt[s] = 1.96 TeV

We report on a first search for production of the lightest neutral CP-even Higgs boson (h) in the next-to-minimal supersymmetric standard model, where h decays to a pair of neutral pseudoscalar Higgs bosons (a), using 4.2 fb;{-1} of data recorded with the D0 detector at Fermilab. The a bosons are required to either both decay to micro;{+}micro;{-} or one to micro;{+}micro;{-} and the other to tau;{+}tau;{-}. No significant signal is observed, and we set limits on its production as functions of M_{a} and M_{h}.

Search for the standard model Higgs boson in tau final states

We present a search for the standard model Higgs boson using hadronically decaying tau leptons, in 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron pp collider. We select two final states: tau+/- plus missing transverse energy and b jets, and tau+ tau- plus jets. These final states are sensitive to a combination of associated W/Z boson plus Higgs boson, vector boson fusion, and gluon-gluon fusion production processes. The observed ratio of the combined limit on the Higgs production cross section at the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of 115 GeV.

Search for resonant diphoton production with the D0 detector

We present a search for a narrow resonance in the inclusive diphoton final state using approximately 2.7 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron pp Collider. We observe good agreement between the data and the background prediction, and set the first 95% C.L. upper limits on the production cross section times the branching ratio for decay into a pair of photons for resonance masses between 100 and 150 GeV. This search is also interpreted in the context of several models of electroweak symmetry breaking with a Higgs boson decaying into two photons.

Measurement of the Zgamma --> nunu[over ]gamma production cross section and limits on anomalous ZZgamma and Zgammagamma couplings in pp[over] collisions at sqrt[s] = 1.96 TeV

We present the first observation of the Zgamma --> nunu[over ]gamma process at the Fermilab Tevatron at 5.1 standard deviations significance, based on 3.6 fb;{-1} of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp[over ] Collider at sqrt[s] = 1.96 TeV. The measured Zgamma production cross section multiplied by the branching fraction of Z --> nunu[over] is 32 +/- 9(stat + syst) +/-2 (lumi) fb for the photon E_{T} > 90 GeV. It is in agreement with the standard model prediction of 39 +/- 4 fb. We set limits on anomalous trilinear Zgammagamma and ZZgamma gauge boson couplings, most of which are the most restrictive to date.

Measurement of gamma+b+X and gamma+c+X Production Cross Sections in pp[over ] Collisions at sqrt[s]=1.96 TeV

First measurements of the differential cross sections d;{3}sigma/(dp_{T};{gamma}dy;{gamma}dy;{jet}) for the inclusive production of a photon in association with a heavy quark (b, c) jet are presented, covering photon transverse momenta 30<p_{T};{gamma}<150 GeV, photon rapidities |y;{gamma}|<1.0, jet rapidities |y;{jet}|<0.8, and jet transverse momenta p_{T};{jet}>15 GeV. The results are based on an integrated luminosity of 1 fb;{-1} in pp[over ] collisions at sqrt[s]=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.

Search for anomalous top-quark couplings with the D0 detector

Anomalous Wtb couplings modify the angular correlations of the top-quark decay products and change the single top-quark production cross section. We present limits on anomalous top-quark couplings by combining information from W boson helicity measurements in top-quark decays and anomalous coupling searches in the single top-quark final state. We set limits on right-handed vector couplings as well as left-handed and right-handed tensor couplings based on about 1 fb(-1) of data collected by the D0 experiment.