We report the observation of a narrow structure, $X(5568)$, in the decay sequence $X(5568) \rightarrow B_s^0 \pi^{\pm}$, $B_s^0 \rightarrow J/\psi \phi$, $J/\psi\rightarrow \mu^+ \mu^-$, $\phi ...\rightarrow K^+K^-$. This is the first observation of a hadronic state with valence quarks of four different flavors. The mass and natural width of the new state are measured to be $m = 5567.8 \pm 2.9 {\rm \thinspace (stat)} ^{+0.9}_{-1.9} {\rm \thinspace (syst)}$ MeV/$c^2$ and $\Gamma = 21.9 \pm 6.4 {\rm \thinspace (stat)} ^{+5.0}_{-2.5} {\rm \thinspace (syst)} $ MeV/$c^2$, and the significance including look-elsewhere effect and systematic uncertainties is 5.1$\sigma$. The observation is based on$10.4~\rm{fb^{-1}}$ of $p \overline p $ collision data at $\sqrt{s}$ = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.
We present constraints on models containing non-standard-model values for the spin J and parity P of the Higgs boson H in up to 9.7 fb(-1) of pp collisions at sqrts = 1.96 TeV collected with the D0 ...detector at the Fermilab Tevatron Collider. These are the first studies of Higgs boson J(P) with fermions in the final state. In the ZH → ℓℓbb, WH → ℓνbb, and ZH → ννbb final states, we compare the standard model (SM) Higgs boson prediction, J(P) = 0(+), with two alternative hypotheses, J(P) = 0(-) and J(P) = 2(+). We use a likelihood ratio to quantify the degree to which our data are incompatible with non-SM J(P) predictions for a range of possible production rates. Assuming that the production rate in the signal models considered is equal to the SM prediction, we reject the J(P) = 0(-) and J(P) = 2(+) hypotheses at the 97.6% CL and at the 99.0% CL, respectively. The expected exclusion sensitivity for a J(P) = 0(-) (J(P) = 2(+)) state is at the 99.86% (99.94%) CL. Under the hypothesis that our data are the result of a combination of the SM-like Higgs boson and either a J(P) = 0(-) or a J(P) = 2(+) signal, we exclude a J(P) = 0(-) fraction above 0.80 and a J(P) = 2(+) fraction above 0.67 at the 95% CL. The expected exclusion covers J(P) = 0(-) (J(P) = 2(+)) fractions above 0.54 (0.47).
We measure the mass of the top quark in lepton+jets final states using the full sample of pp collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at sqrts = 1.96 ...TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from tt production or background. The overall jet energy scale is constrained in situ by the mass of the W boson. We measure m(t) = 174.98 ± 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.
We measure the cross section and the difference in rapidities between photons and charged leptons for inclusive W({yields}l{nu})+{gamma} production in e{gamma} and {mu}{gamma} final states. Using ...data corresponding to an integrated luminosity of 4.2 fb{sup -1} collected with the D0 detector at the Fermilab Tevatron Collider, the measured cross section times branching fraction for the process pp{yields}W{gamma}+X{yields}l{nu}{gamma}+X 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 WW{gamma} couplings for data from hadron colliders: -0.4<{Delta}{kappa}{sub {gamma}<}0.4 and -0.08<{lambda}{sub {gamma}<}0.07 at the 95% C.L.
We present a search for the standard model Higgs boson and a fermiophobic Higgs boson in the diphoton final states based on 8.2 fb{sup -1} of pp collisions at {radical}(s)=1.96 TeV collected with the ...D0 detector at the Fermilab Tevatron Collider. No excess of data above background predictions is observed and upper limits at the 95% C.L. on the cross section multiplied by the branching fraction are set which are the most restrictive to date. A fermiophobic Higgs boson with a mass below 112.9 GeV is excluded at the 95% C.L.
We report results from a search for neutral Higgs bosons produced in association with b quarks using data recorded by the D0 experiment at the Fermilab Tevatron Collider and corresponding to an ...integrated luminosity of 7.3 fb{sup -1}. This production mode can be enhanced in several extensions of the standard model (SM) such as in its minimal supersymmetric extension (MSSM) at high tan{beta}. We search for Higgs bosons decaying to tau pairs with one tau decaying to a muon and neutrinos and the other to hadrons. The data are found to be consistent with SM expectations, and we set upper limits on the cross section times branching ratio in the Higgs boson mass range from 90 to 320 GeV/c{sup 2}. We interpret our result in the MSSM parameter space, excluding tan{beta} values down to 25 for Higgs boson masses below 170 GeV/c{sup 2}.
We search for resonant WW or WZ production by using up to 5.4 fb{sup -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{sup '} boson and the Randall-Sundrum model graviton G as benchmarks. We exclude a sequential standard model W{sup '} boson in the mass range 180-690 GeV and a Randall-Sundrum graviton in the range 300-754 GeV at 95% C.L.
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{sup -1} collected ...with the D0 detector at {radical}(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{sup 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{sup 2} is 8x10{sup -6}.
We present a search for the standard model Higgs boson (H) in pp collisions at {radical}(s)=1.96 TeV in events containing a charged lepton (l), missing transverse energy, and at least two jets, using ...5.4 fb{sup -1} of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primarily to Higgs bosons produced through the fusion of two gluons or two electroweak bosons, with subsequent decay H{yields}WW{yields}l{nu}q{sup '}q, where l is an electron or muon. The search is also sensitive to contributions from other production channels, such as WH{yields}l{nu}bb. In the absence of a signal, we set limits at the 95% C.L. on the cross section for H production {sigma}(pp{yields}H+X) in these final states. For a mass of M{sub H}=160 GeV, the limit is a factor of 3.9 larger than the cross section in the standard model and consistent with an a priori expected sensitivity of 5.0.
Using 7.3 fb{sup -1} of pp collisions collected by the D0 detector at the Fermilab Tevatron, we measure the distribution of the variable {phi}{sub {eta}*}, which probes the same physical effects as ...the Z/{gamma}* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. A QCD prediction is found to describe the general features of the {phi}{sub {eta}*} distribution, but is unable to describe its detailed shape or dependence on boson rapidity. A prediction that includes a broadening of transverse momentum for small values of the parton momentum fraction is strongly disfavored.
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