20 Search Results

Here, we study $$\Lambda$$ and $$\bar{\Lambda}$$ production asymmetries in $$p \bar{p} \rightarrow \Lambda (\bar{\Lambda}) X$$, $$p \bar{p} \rightarrow J/\psi \Lambda (\bar{\Lambda}) X$$, and $$p \bar{p} \rightarrow \mu^\pm \Lambda (\bar{\Lambda}) X$$ events recorded by the D0 detector at the Fermilab Tevatron collider at $$\sqrt{s} = 1.96$$ TeV. We find an excess of $$\Lambda$$'s ($$\bar{\Lambda}$$'s) produced in the proton (antiproton) direction. This forward-backward asymmetry is measured as a function of rapidity. We confirm that the $$\bar{\Lambda}/\Lambda$$ production ratio, measured by several experiments with various targets and a wide range of energies, is a universal function of "rapidity loss", i.e., the rapidity differencemore » of the beam proton and the lambda.« less

We present a study of the inclusive production of the X(4140) state with the decay to the J/ψΦ final state in hadronic collisions. Based on 10.4 fb^-1 of pp¯ collision data collected by the D0 experiment at the Fermilab Tevatron collider, we report the first evidence for the prompt production of an X(4140)state and find the fraction of X(4140) events originating from b hadrons to be f_b=0.39±0.07(stat)±0.10(syst). The ratio of the nonprompt X(4140) production rate to the B⁰_syield in the same channel is R=0.19±0.05(stat)±0.07(syst). Furthermore, the values of the mass M=4152.5±1.7(stat)^+6.2_-5.4(syst) MeV and width Γ=16.3±5.6(stat)±11.4(syst) MeV are consistent with previousmore » measurements.« less

We present the first search for CPT-violating effects in the mixing of B⁰_s mesons using the full Run II data set with an integrated luminosity of 10.4 fb^-1 of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. We measure the CPT-violating asymmetry in the decay B⁰_s → µ^±D^±_s as a function of celestial direction and sidereal phase. We find no evidence for CPT-violating effects and place limits on the direction and magnitude of flavor-dependent CPTand Lorentz-invariance violating coupling coefficients. We find 95% confidence intervals of Δa⊥ < 1.2 × 10^-12 GeV and (-0.8 < ΔaT -more » 0.396Δa_Z < 3.9) × 10^-13 GeV.« less

We present a simultaneous measurement of the forward-backward asymmetry and the top-quark polarization in tt¯ production in dilepton final states using 9.7 fb^–1 of proton-antiproton collisions at √s=1.96 TeV with the D0 detector. To reconstruct the distributions of kinematic observables we employ a matrix element technique that calculates the likelihood of the possible tt¯ kinematic configurations. After accounting for the presence of background events and for calibration effects, we obtain a forward-backward asymmetry of A^tt¯=(15.0±6.4(stat)±4.9(syst))% and a top-quark polarization times spin analyzing power in the beam basis of κP=(7.2±10.5(stat)±4.2(syst))%, with a correlation of –56% between the measurements. If we constrainmore » the forward-backward asymmetry to its expected standard model value, we obtain a measurement of the top polarization of κP=(11.3±9.1(stat)±1.9(syst))%. If we constrain the top polarization to its expected standard model value, we measure a forward-backward asymmetry of A^tt¯=(17.5±5.6(stat)±3.1(syst))%. A combination with the D0 A^tt¯ measurement in the lepton+jets final state yields an asymmetry of Att¯=(11.8±2.5(stat)±1.3(syst))%. Within their respective uncertainties, all these results are consistent with the standard model expectations.« less

The recent paper on the charge asymmetry for electrons from W boson decay has an error in the Tables VII to XI that show the correlation coefficients of systematic uncertainties. Furthermore, the correlation matrix elements shown in the original publication were the square roots of the calculated values.

We present a measurement of the distribution of the variable φ*_η for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb^–1 at √s = 1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable φ*_η probes the same physical effects as the Z/γ* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurementsmore » at any collider of the φ*_η distributions for dilepton masses away from the Z → ℓ⁺ℓ^– boson mass peak. As a result, the data are compared to QCD predictions based on the resummation of multiple soft gluons.« less

We present a measurement of the forward-backward asymmetry in the production of B^± mesons, A_FB(B^±), using B^± → J/ψK^± decays in 10.4 fb^-1 of pp¯ collisions at √s = 1.96 TeV collected by the D0 experiment during Run II of the Tevatron collider. A nonzero asymmetry would indicate a preference for a particular flavor, i.e., b quark or b¯ antiquark, to be produced in the direction of the proton beam. We extract A_FB(B^±) from a maximum likelihood fit to the difference between the numbers of forward- and backward-produced B^± mesons. We measure an asymmetry consistent with zero: A_FB(B^±) = [-0.24more » ± 0.41 (stat) ± 0.19 (syst)]%.« less

In this study, 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 $$p\bar{p}$$ collisions at $$\sqrt{s} = $$ 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 $$ZH\rightarrow \ell\ell b\bar{b}$$, $$WH\rightarrow \ell\nu b\bar{b}$$, and $$ZH\rightarrow \nu\nu b\bar{b}$$ 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 themore » 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 is 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).« less

We present a search for the standard model (SM) Higgs boson produced in association with a Z boson in 9.7 fb^-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt(s) = 1.96 TeV. Selected events contain one reconstructed Z → e⁺e⁻ or Z → μ⁺μ⁻ candidate and at least two jets, including at least one jet identified as likely to contain a b quark. To validate the search procedure, we also measure the cross section for ZZ production in the same final state. It is found to be consistent with its SM prediction. Wemore » set upper limits on the ZH production cross section times branching ratio for H → $$b\bar{b}$$ at the 95% C.L. for Higgs boson masses 90 < $$M_H$$ < 150 GeV. Lastly, the observed (expected) limit for $$M_H$$ = 125 GeV is 7.1 (5.1) times the SM cross section.« less