Search Results (435 total)

We report on a search for large extra dimensions in a data sample of approximately 1  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV. We investigate Kaluza-Klein graviton production with a photon and missing transverse energy in the final state. At the 95% C.L. we set limits on the fundamental mass scale M_D from 884 to 778 GeV for two to eight extra dimensions.

Using a 492  fb^-1 data sample collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider, we observe the decay B⁰→pp̅ K^*0 with a branching fraction of (1.18_-0.25^+0.29(stat)±0.11(syst))×10^-6. We study the decay dynamics of B⁰→pp̅ K^*0 and compare with B⁺→pp̅ K^*+. The K^*0 meson is found to be almost 100% polarized (with a fraction of (101±13±3)% in the helicity zero state), while the K^*+ meson has a (32±17±9)% fraction in the helicity zero state. The direct CP asymmetries for B⁰→pp̅ K^*0 and B⁺→pp̅ K^*+ are measured to be -0.08±0.20±0.02 and -0.01±0.19±0.02, respectively. In addition, we report improved measurements of the branching fractions B(B⁺→pp̅ K^*+)=(3.38_-0.60^+0.73±0.39)×10^-6 and B(B⁰→pp̅ K⁰)=(2.51_-0.29^+0.35±0.21)×10^-6, which supersede our previous measurements.

We present results from a study of pp̅ →Wγ+X events utilizing data corresponding to 0.7  fb^-1 of integrated luminosity at sqrt[s]=1.96  TeV collected by the D0 detector at the Fermilab Tevatron Collider. We set limits on anomalous WWγ couplings at the 95% C.L. The one-dimensional 95% C.L. limits are 0.49<κ_γ<1.51 and -0.12<λ_γ<0.13. We make the first study of the charge-signed rapidity difference between the lepton and the photon and find it to be indicative of the standard model radiation-amplitude zero in the Wγ system.

We report a search for R-parity-violating production and decay of sneutrino particles in the eμ final state with 1.04±0.06  fb^-1 of data collected with the D₀ detector at the Fermilab Tevatron Collider in 2002–2006. Good agreement between the data and the standard model prediction is observed. With no evidence for new physics, we set limits on the R-parity-violating couplings λ₃₁₁^′ and λ₃₁₂ as a function of the sneutrino mass.

In order to clarify whether VO₂ is a Mott insulator or a Peierls insulator, the metal-insulator transition (MIT) and the structural phase transition (SPT) are simultaneously monitored for VO₂ films by current-voltage curve and diffraction measurements using a synchrotron micro-x-ray beam. In the regime showing a metallic conductivity below the SPT temperature (approximately 70 °C), only the diffraction planes of the monoclinic structure are observed, while planes of the tetragonal structure are absent. This observation reveals the presence of a monoclinic and metal phase between the MIT and the SPT as a characteristic of a Mott insulator.

We search for the production of a heavy W^′ gauge boson that decays to third generation quarks in 0.9  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W^′ boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W^′ bosons, we set lower mass limits of 739 GeV if the W^′ boson decays to both leptons and quarks and 768 GeV if the W^′ boson decays only to quarks. We also set limits on the coupling of the W^′ boson to fermions as a function of its mass.

We present a search for direct CP violation in B^±→J/ψK^±(π^±) decays. The event sample is selected from 2.8  fb^-1 of pp̅ collisions recorded by D0 experiment in run II of the Fermilab Tevatron Collider. The charge asymmetry A_CP(B⁺→J/ψK⁺)=+0.0075±0.0061(stat)±0.0030(syst) is obtained using a sample of approximately 40 000 B^±→J/ψK^± decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry A_CP(B⁺→J/ψπ⁺)=-0.09±0.08(stat)±0.03(syst).

We show that a dynamically evolving two-mode Bose-Einstein condensate (TBEC) with an adiabatic, time-varying Raman coupling maps exactly onto a Ramsey interferometer that includes a nonlinear medium. Assuming a realistic quantum state for the TBEC that has been achieved experimentally, we find that the measurement uncertainty of the “path-difference” phase shift scales as the standard quantum limit (1/sqrt[N]), where N is the number of atoms, while that for the interatomic scattering strength scales as 1/N^7/5, overcoming the conventional Heisenberg limit of 1/N.

We measure the tt̅ production cross section in pp̅ collisions at sqrt[s]=1.96  TeV in the lepton+jets channel. Two complementary methods discriminate between signal and background: b tagging and a kinematic likelihood discriminant. Based on 0.9  fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure σ_tt̅ =7.62±0.85  pb, assuming the current world average m_t=172.6  GeV. We compare our cross section measurement with theory predictions to determine a value for the top-quark mass of 170±7  GeV.

We present the first simultaneous measurement of the ratio of branching fractions, R=B(t→Wb)/B(t→Wq), with q being a d, s, or b quark, and the top-quark pair production cross section σ_tt̅ in the lepton plus jets channel using 0.9  fb^-1 of pp̅ collision data at sqrt[s]=1.96  TeV collected with the D0 detector. We extract R and σ_tt̅ by analyzing samples of events with 0, 1, and ≥2 identified b jets. We measure R=0.97_-0.08^+0.09(stat+syst) and σ_tt̅ =8.18_-0.84^+0.90(stat+syst)±0.50(lumi)  pb, in agreement with the standard model prediction.

We present the results of a search for the production of an excited state of the electron, e^*, in proton-antiproton collisions at sqrt[s]=1.96  TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1  fb^-1. We search for e^* in the process pp̅ →e^*e, with the e^* subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e^* production by four-fermion contact interactions and e^* decay via electroweak processes, we set 95% C.L. upper limits on the production cross section ranging from 8.9 to 27 fb, depending on the mass of the excited electron. Choosing the scale for contact interactions to be Λ=1  TeV, excited electron masses below 756 GeV are excluded at the 95% C.L.

We report an improved measurement of the B⁺→D⁺D̅ ⁰ and B⁰→D⁰D̅ ⁰ decays based on 657×10⁶ BB̅ events collected with the Belle detector at KEKB. We measure the branching fraction and charge asymmetry for the B⁺→D⁺D̅ ⁰ decay: B(B⁺→D⁺D̅ ⁰)=(3.85±0.31±0.38)×10^-4 and A_CP(B⁺→D⁺D̅ ⁰)=0.00±0.08±0.02, where the first error is statistical and the second is systematic. We also set the upper limit for the B⁰→D⁰D̅ ⁰ decay: B(B⁰→D⁰D̅ ⁰)<0.43×10^-4 at 90% CL.

We study both numerically and analytically the possibility of using an adiabatic passage control method to construct a Mach-Zehnder interferometer (MZI) for Bose-Einstein condensates in the time domain, in exact one-to-one correspondence with the traditional optical MZI that involves two beam splitters and two mirrors. The interference fringes one obtains from such a minimum-disturbance setup clearly demonstrates that, fundamentally, an atom laser is not monochromatic due to interatomic interactions. We also consider how the amount of entanglement in the system correlates to the interference fringes.

We present the first measurement of the integrated forward-backward charge asymmetry in top-quark–top-antiquark pair (tt̅ ) production in proton-antiproton (pp̅ ) collisions in the lepton+jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming tt̅ +X production and decay, a sample of 0.9  fb^-1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on tt̅ +X production via a Z^′ resonance.

A distinct peak is observed in the π^±ψ^′ invariant mass distribution near 4.43 GeV in B→Kπ^±ψ^′ decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of M=4433±4(stat)±2(syst)  MeV and Γ=45_-13⁺¹⁸(stat)_-13⁺³⁰(syst)  MeV. The product branching fraction is determined to be B(B⁰→K^∓Z^±(4430))×B(Z^±(4430)→π^±ψ^′)=(4.1±1.0(stat)±1.4(syst))×10^-5, where Z^±(4430) is used to denote the observed structure. The statistical significance of the observed peak is 6.5σ. These results are obtained from a 605  fb^-1 data sample that contains 657×10⁶ BB̅ pairs collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e⁺e^- collider.

We present the results of a time-dependent Dalitz plot analysis of B⁰→π⁺π^-π⁰ decays based on a 414  fb^-1 data sample that contains 449×10⁶BB̅ pairs. The data were collected on the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e⁺e^- collider. Combining our analysis with information on charged B decay modes, we perform a full Dalitz and isospin analysis and obtain a constraint on the quark mixing angle ϕ₂, 68°<ϕ₂<95° at the 68.3% confidence level for the ϕ₂ solution consistent with the standard model. A large standard-model–disfavored region also remains. The branching fractions for the decay processes B⁰→ρ^±(770)π^∓ and B⁰→ρ⁰(770)π⁰ are measured to be (22.6±1.1[stat]±4.4[syst])×10^-6 and (3.0±0.5[stat]±0.7[syst])×10^-6, respectively. These are the first branching fraction measurements of the process B⁰→ρ(770)π with the lowest resonance ρ(770) explicitly separated from the radial excitations.

We present a study of μμμμ, eeee, and μμee events using 1  fb^-1 of data collected with the D0 detector at the Fermilab Tevatron pp̅ Collider at sqrt[s]=1.96  TeV. Requiring the lepton pair masses to be greater than 30 GeV, we observe one event, consistent with the expected background of 0.13±0.03 events and with the predicted standard model ZZ and Zγ^* production of 1.71±0.15 events. We set an upper limit on the ZZ and Zγ^* cross section of 4.4 pb at the 95% C.L. We also derive limits on anomalous neutral trilinear ZZZ and ZZγ^* gauge couplings. The one-parameter 95% C.L. coupling limits with a form-factor scale Λ=1.2  TeV are -0.28<f₄₀^Z<0.28, -0.31<f₅₀^Z<0.29, -0.26<f₄₀^γ<0.26, and -0.30<f₅₀^γ<0.28.

We report improved measurements of time-dependent CP violation parameters for B⁰(B̅ ⁰)→J/ψπ⁰ decay. This analysis is based on 535×10⁶ BB̅ pairs accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. From the distribution of proper time intervals between the two B decays, we obtain the following CP violation parameters S_J/ψπ⁰=-0.65±0.21(stat)±0.05(syst)  and  A_J/ψπ⁰=+0.08±0.16(stat)±0.05(syst),which are consistent with standard model expectations.

We report on a near-field amplification in a transmission metallic grating, whereby the spatially and spectrally resolved near-field intensity reaches ∼20 times the incident intensity at the surface plasmon polariton resonance. The amplified value is maintained up to ∼2  μm away from the surface. Our experiments show that the near-field amplification in the transmission grating, which is strongly implied in a recent superlens design, indeed occurs at the surface plasmon polariton resonance. Theoretical calculation shows good agreement with experiment and also reveals that the horizontal magnetic field is predominantly amplified. Our results suggest that a grating-assisted superlens should have its optimal functional wavelength right around the surface plasmon resonance.

Indium kinetics and evidence for indium segregation on the GaN (0001) surface are investigated via in situ spectroscopic ellipsometry. Indium deposition exhibits two stable states at coverages of 1.0 and 1.7 ML within the temperature range of 630–688  °C. Formation of each layer is governed by two kinetic processes: nuclei formation and nuclei-mediated layer adsorption. The measured desorption activation energies of nuclei of the first (2.04  eV) and second (2.33  eV) monolayers are lower than the desorption activation energies of the aggregated first (2.64  eV) and second (2.53  eV) monolayers, respectively. This suggests that adatoms preferentially interact with the nuclei and laterally aggregate.

We study the flavor-changing-neutral-current process c→uμ⁺μ^- using 1.3  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We see clear indications of the charged-current mediated D_s⁺ and D⁺→ϕπ⁺→μ⁺μ^-π⁺ final states with significance greater than 4 standard deviations above background for the D⁺ state. We search for the continuum neutral-current decay of D⁺→π⁺μ⁺μ^- in the dimuon invariant mass spectrum away from the ϕ resonance. We see no evidence of signal above background and set a limit of B(D⁺→π⁺μ⁺μ^-)<3.9×10^-6 at the 90% C.L. This limit places the most stringent constraint on new phenomena in the c→uμ⁺μ^- transition.

We present a measurement of the shape of the Z/γ^* boson transverse momentum (q_T) distribution in pp̅ →Z/γ^*→e⁺e^-+X events at a center-of-mass energy of 1.96 TeV using 0.98  fb^-1 of data collected with the D0 detector at the Fermilab Tevatron collider. The data are found to be consistent with the resummation prediction at low q_T, but above the perturbative QCD calculation in the region of q_T>30  GeV/c. Using events with q_T<30  GeV/c, we extract the value of g₂, one of the nonperturbative parameters for the resummation calculation. Data at large boson rapidity y are compared with the prediction of resummation and with alternative models that employ a resummed form factor with modifications in the small Bjorken x region of the proton wave function.

The multiform donor nature of hydrogen in n-type indium nitride is experimentally observed in samples exposed to atomic hydrogen. Photoluminescence measurements reveal a tenfold increase in the electron concentration and the formation of a shallow donor band upon hydrogen incorporation. Annealing studies show that hydrogen occupies at least two equilibrium sites having almost equivalent thermal stability.

We search for decays of Kaluza-Klein excitations of the graviton in the Randall-Sundrum model of extra dimensions to e⁺e^- and γγ in 1  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV collected by the D0 detector at the Fermilab Tevatron. We set 95% confidence level upper limits on the production cross section times branching fraction, which translate into lower limits on the mass of the lightest excitation between 300 and 900 GeV for values of the coupling k/M̅ _Pl between 0.01 and 0.1.