Azimuthal decorrelations and multiple parton interactions in photon+2 jet and photon+3 jet events in ppbar collisions at sqrt{s}=1.96 TeV

Samples of inclusive photon+2 jet and photon+3 jet events collected by the D0 experiment with an integrated luminosity of about 1fb^-1 in ppbar collisions at sqrt{s}=1.96 TeV are used to measure cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (pT) of the photon+leading jet system (jets are ordered in pT) and pT of the other jet for photon+2 jet, or pT sum of the two other jets for photon+3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the PYTHIA and SHERPA Monte Carlo (MC) generators. The data indicate a contribution from events with double parton (DP) interactions and are well described by predictions provided by the PYTHIA MPI models with pT-ordered showers and by SHERPA with the default MPI model. The photon+2 jet data are also used to determine the fraction of events with DP interactions as a function of the azimuthal angle and as a function of the second jet pT

Measurement of the W boson mass

We present a measurement of the W boson mass in W -> ev 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 -> ev candidate events, we measure M_W = 80.401 +- 0.043 GeV. This is the most precise measurement from a single experiment

Measurement of the t-channel single top quark production cross section

The D0 collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb^-1 of ppbar collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14 +0.94 -0.80 pb for the t-channel and 1.05 +-0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction

A Novel method for modeling the recoil in W boson events at hadron collider

We present a new method for modeling the hadronic recoil in W->lnu events produced at hadron colliders. The recoil is chosen from a library of recoils in Z->ll data events and overlaid on a simulated W->lnu event. Implementation of this method requires that the data recoil library describe the properties of the measured recoil as a function of the true, rather than the measured, transverse momentum of the boson. We address this issue using a multidimensional Bayesian unfolding technique. We estimate the statistical and systematic uncertainties from this method for the W boson mass and width measurements assuming 1 fb-1 of data from the Fermilab Tevatron. The uncertainties are found to be small and comparable to those of a more traditional parameterized recoil model. For the high precision measurements that will be possible with data from Run II of the Fermilab Tevatron and from the CERN LHC, the method presented in this paper may be advantageous, since it does not require an understanding of the measured recoil from first principles

Measurement of Z/gamma*+jet+X angular distributions in p anti-p collisions at s**(1/2) = 1.96.TeV

We present the first measurements at a hadron collider of differential cross sections for Z+jet+X production in delta phi(Z, jet), |delta y(Z, jet)| and |y_boost(Z, jet)|. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals

Measurement of the ratio of differential cross sections σ(ppˉ→Z+bjet)/σ(ppˉ→Z+jet){\sigma}(p\bar{p} \to Z + b jet)/{\sigma}(p\bar{p} \to Z + jet) in ppˉp\bar{p} collisions at (s)=1.96\sqrt(s)=1.96 TeV

We measure the ratio of cross sections, {\sigma}(ppbar -> Z + b jet)/{\sigma}(ppbar -> Z + jet), for associated production of a Z boson with at least one jet. The ratio is also measured as a function of the jet transverse momentum, jet pseudorapidity, Z boson transverse momentum, and the azimuthal angle between the Z boson and the closest jet for events with at least one b jet. These measurements use data collected by the D0 experiment in Run II of Fermilab's Tevatron ppbar Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of 9.7 fb$^{-1}$. The results are compared to predictions from next-to-leading order calculations and various Monte Carlo event generators

WγW\gamma production and limits on anomalous WWγWW\gamma couplings in ppˉp\bar{p} collisions

We measure the cross section and the difference in rapidities between photons and charged leptons for inclusive W -> lnu+gamma production in egamma and mugamma final states. Using data corresponding to an integrated luminosity of 4.2 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider, the cross section multiplied by the branching fraction for the process ppbar -> Wgamma+X -> lnugamma+X, measured to be 15.8 +/- 0.8 (stat.) +/- 1.2 (syst.) pb, and the distribution of the charge-signed photon-lepton rapidity difference are found to be in agreement with the standard model. These results provide the most stringent limits on anomalous WWgamma couplings for data from hadron colliders: -0.4 < Delta kappa_gamma < 0.4 and -0.08 < lambda_gamma < 0.07 at the 95% C.L

Measurement of three-jet differential cross sections dσ3jet/dM3jetd\sigma_{\text{3jet}} / dM_{\text{3jet}} in ppˉp\bar{p} collisions at s=1.96\sqrt{s}=1.96 TeV

We present the first measurement of the inclusive three-jet differential cross section as a function of the invariant mass of the three jets with the largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96 TeV. The measurement is made in different rapidity regions and for different jet transverse momentum requirements and is based on a data set corresponding to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at the Fermilab Tevatron Collider. The results are used to test the three-jet matrix elements in perturbative QCD calculations at next-to-leading order in the strong coupling constant. The data allow discrimination between parametrizations of the parton distribution functions of the proton.We present the first measurement of the inclusive three-jet differential cross section as a function of the invariant mass of the three jets with the largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96 TeV. The measurement is made in different rapidity regions and for different jet transverse momentum requirements and is based on a data set corresponding to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at the Fermilab Tevatron Collider. The results are used to test the three-jet matrix elements in perturbative QCD calculations at next-to-leading order in the strong coupling constant. The data allow discrimination between parametrizations of the parton distribution functions of the proton

Search for doubly-charged Higgs boson pair production in ppbar collisions at sqrt{s} = 1.96 TeV

We present a search for pair production of doubly-charged Higgs bosons in the processes $q\bar{q} \to {H}^{++}{H}^{--}$ decaying through ${H}^{\pm\pm} \to \tau^{\pm}\tau^{\pm}, \mu^{\pm}\tau^{\pm}, \mu^{\pm}\mu^{\pm}$. The search is performed in ${p}\overline{p}$ collisions at a center-of-mass energy of $\sqrt{s}=1.96$~TeV using an integrated luminosity of $7.0$~fb$^{-1}$ collected by the D0 experiment at the Fermilab Tevatron Collider. The results are used to set $95\%$ C.L.~limits on the pair production cross section of doubly-charged Higgs bosons and on their mass for different ${H}^{\pm\pm}$ branching fractions. Models predicting different ${H}^{\pm\pm}$ decays are investigated. Assuming ${\cal B}({H}^{\pm\pm}\to\tau^{\pm}\tau^{\pm})=1$ yields an observed (expected) lower limit on the mass of a left-handed ${H}^{\pm\pm}_L$ boson of 128 (116)~GeV and assuming ${\cal B}({H}^{\pm\pm}\to\mu^{\pm}\tau^{\pm})=1$ the corresponding limits are 144 (149)~GeV. In a model with ${\cal B}({H}^{\pm\pm} \to \tau^{\pm}\tau^{\pm})={\cal B}({H}^{\pm\pm}\to\ mu^{\pm}\tau^{\pm})={\cal B}({H}^{\pm\pm}\to\mu^{\pm}\mu^{\pm})=1/3$, we obtain $M({H}^{\pm\pm}_L)>130~(138)$~GeV.We present a search for pair production of doubly-charged Higgs bosons in the processes $q\bar{q} \to {H}^{++}{H}^{--}$ decaying through ${H}^{\pm\pm} \to \tau^{\pm}\tau^{\pm}, \mu^{\pm}\tau^{\pm}, \mu^{\pm}\mu^{\pm}$. The search is performed in ${p}\overline{p}$ collisions at a center-of-mass energy of $\sqrt{s}=1.96$~TeV using an integrated luminosity of $7.0$~fb$^{-1}$ collected by the D0 experiment at the Fermilab Tevatron Collider. The results are used to set $95\%$ C.L.~limits on the pair production cross section of doubly-charged Higgs bosons and on their mass for different ${H}^{\pm\pm}$ branching fractions. Models predicting different ${H}^{\pm\pm}$ decays are investigated. Assuming ${\cal B}({H}^{\pm\pm}\to\tau^{\pm}\tau^{\pm})=1$ yields an observed (expected) lower limit on the mass of a left-handed ${H}^{\pm\pm}_L$ boson of 128 (116)~GeV and assuming ${\cal B}({H}^{\pm\pm}\to\mu^{\pm}\tau^{\pm})=1$ the corresponding limits are 144 (149)~GeV. In a model with ${\cal B}({H}^{\pm\pm} \to \tau^{\pm}\tau^{\pm})={\cal B}({H}^{\pm\pm}\to\ mu^{\pm}\tau^{\pm})={\cal B}({H}^{\pm\pm}\to\mu^{\pm}\mu^{\pm})=1/3$, we obtain $M({H}^{\pm\pm}_L)>130~(138)$~GeV

Search for Higgs boson production in oppositely charged dilepton and missing energy final states in 9.7 fb−1^{-1} of ppˉp\bar{p} collisions at s=1.96\sqrt{s} = 1.96 TeV

We present a search for Higgs boson in final states with two oppositely charged leptons and large missing transverse energy as expected in H -> WW -> lvlv decays. The events are selected from the full Run II data sample of 9.7 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt s = 1.96 TeV. To validate our search methodology, we measure the non-resonant W W production cross section and find sigma_WW = 11.6 +/- 0.7 pb, in agreement with the standard model prediction. In the Higgs boson search, no significant excess above the background expectation is observed. Upper limits at the 95% confidence level on the Higgs boson production cross section are therefore derived. Within the standard model, the Higgs boson mass range 159 < MH < 176 GeV is excluded while the expected exclusion sensitivity is 156 < MH < 172 GeV. For a mass hypothesis of MH = 125 GeV, we exclude Higgs boson production cross sections 4.1 times larger than the standard model expectation, which is compatible with the presence of a Higgs boson at this mass. Within a theoretical framework with a fourth generation of fermions, the mass range 125 < MH < 218 GeV is excluded. The search results are also interpreted in the context of fermiophobic Higgs boson couplings, which yields an exclusion of fermiophobic Higgs boson production cross sections 3.1 times larger than the expectation for MH = 125 GeV