Search Results (997 total)

We present the first measurement of dijet angular distributions in pp̅ collisions at sqrt[s]=1.96  TeV at the Fermilab Tevatron Collider. The measurement is based on a dataset corresponding to an integrated luminosity of 0.7  fb^-1 collected with the D0 detector. Dijet angular distributions have been measured over a range of dijet masses, from 0.25 TeV to above 1.1 TeV. The data are in good agreement with the predictions of perturbative QCD and are used to constrain new physics models including quark compositeness, large extra dimensions, and TeV^-1 scale extra dimensions. For all models considered, we set the most stringent direct limits to date.

We provide the most precise measurement of the WW production cross section in pp̅ collisions to date at a center of mass energy of 1.96 TeV, and set limits on the associated trilinear gauge couplings. The WW→ℓνℓ^′ν (ℓ, ℓ^′=e, μ) decay channels are analyzed in 1  fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. The measured cross section is σ(pp̅ →WW)=11.5±2.1(stat+syst)±0.7(lumi)  pb. One- and two-dimensional 95% C.L. limits on trilinear gauge couplings are provided.

We combine measurements of the top quark pair production cross section in pp̅ collisions in the ℓ+jets, ℓℓ, and τℓ final states (where ℓ is an electron or muon) at a center of mass energy of sqrt[s]=1.96  TeV in 1  fb^-1 of data collected with the D0 detector. For a top quark mass of 170  GeV/c², we obtain σ_tt̅ =8.18_-0.87^+0.98  pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined tt̅ cross section, consistent with the world average of the top quark mass. In addition, the ratios of tt̅ cross sections in different final states are used to set upper limits on the branching fractions B(t→H⁺b→τ⁺νb) and B(t→H⁺b→cs̅ b) as a function of the charged Higgs boson mass.

A comparative study of the upper critical field H_c2 and second magnetization peak H_sp was performed using high-quality single crystals of hole-doped Ba_0.68K_0.32Fe₂As₂ and electron-doped BaFe_1.85Co_0.15As₂ and BaFe_1.91Ni_0.09As₂. The H_c2 was extracted from both resistivity and magnetization measurements using varying magnetic fields on H∥c and H⊥c orientations. The anisotropic ratio, γ=H_c2^⊥c/H_c2^∥c, was observed to decrease to ∼2.5 for the hole-doped and ∼3.0 for both electron-doped samples as the magnetic fields were increased up to 9 T. It demonstrates that the anisotropic properties only show slight change by doping aliovalent ions either in or out-of the basal plane of FeAs. For the hole-doped Ba_0.68K_0.32Fe₂As₂ the H_c2 and H_sp shift toward the higher temperature and higher field regime in the temperature-normalized (T/T_c) vortex phase diagram, suggesting a stronger vortex pinning by the comparison with the electron-doped BaFe_1.85Co_0.15As₂ and BaFe_1.91Ni_0.09As₂. In contrast to the As-deficiency or inhomogeneous doping distribution of K, Co, and Ni, the dense pinning centers in Ba_0.68K_0.32Fe₂As₂ may be attributed to the disordered structural domains and suggested to be responsible for the intrinsic disorder and anisotropy of iron arsenides.

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

We present a search for charged Higgs bosons in decays of top quarks, in the mass range 80<m_H^±<155  GeV, assuming the subsequent decay H⁺→τ⁺ν_τ (and its charge conjugate). Using 0.9  fb^-1 of lepton+jets data collected with the D0 detector at the Fermilab Tevatron pp̅ collider, operating at a center of mass energy sqrt[s]=1.96  TeV, we find no evidence for a H^± signal. Hence we exclude branching ratios B(t→H⁺b)>0.24 for m_H^±=80  GeV and B(t→H⁺b)>0.19 for m_H^±=155  GeV at the 95% C.L.

We present experimental heat transport measurements of turbulent Rayleigh-Bénard convection with rotation about a vertical axis. The fluid, water with a Prandtl number (σ) of about 6, was confined in a cell with a square cross section of 7.3×7.3 cm² and a height of 9.4 cm. Heat transport was measured for Rayleigh numbers 2×10⁵<Ra<5×10⁸ and Taylor numbers 0<Ta<5×10⁹. We show the variation in normalized heat transport, the Nusselt number, at fixed dimensional rotation rate Ω_D, at fixed Ra varying Ta, at fixed Ta varying Ra, and at fixed Rossby number Ro. The scaling of heat transport in the range of 10⁷ to about 10⁹ is roughly 0.29 with a Ro-dependent coefficient or equivalently is also well fit by a combination of power laws of the form a Ra^1/5+b Ra^1/3. The range of Ra is not sufficient to differentiate single power law or combined power-law scaling. The data are roughly consistent with an assumption that the enhancement of heat transport owing to rotation is proportional to the number of vortical structures penetrating the boundary layer. We also compare indirect measures of thermal and Ekman boundary layer thicknesses to assess their potential role in controlling heat transport in different regimes of Ra and Ta.

We present a direct measurement of trilinear gauge boson couplings at γWW and ZWW vertices in WW and WZ events produced in pp̅ collisions at sqrt[s]=1.96  TeV. We consider events with one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1.1  fb^-1 of integrated luminosity. Considering two different relations between the couplings at the γWW and ZWW vertices, we measure these couplings at 68% C.L. to be κ_γ=1.07_-0.29^+0.26, λ=0.00_-0.06^+0.06, and g₁^Z=1.04_-0.09^+0.09 in a scenario respecting SU(2)_L⊗U(1)_Y gauge symmetry and κ=1.04_-0.11^+0.11 and λ=0.00_-0.06^+0.06 in an “equal couplings” scenario.

We present a measurement of the mass difference between t and t̅ quarks in lepton+jets final states of tt̅ events in 1  fb^-1 of data collected with the D0 detector from Fermilab Tevatron Collider pp̅ 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 t̅ masses. This is the first direct measurement of a mass difference between a quark and its antiquark partner.

We present a measurement of the D⁰-D̅ ⁰ mixing parameter y_CP using a flavor-untagged sample of D⁰→K_S⁰K⁺K^- decays. The measurement is based on a 673  fb^-1 data sample recorded with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. Using a method based on measuring the mean decay time for different K⁺K^- invariant mass intervals, we find y_CP=(+0.11±0.61(stat.)±0.52(syst.))%.

We report a measurement of the exclusive B⁺ meson decay to the D_s^(*)-K⁺π⁺ final state using 657×10⁶BB̅ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We use D_s^*-→D_s^-γ and the D_s^-→ϕπ^-, K̅ ^*(892)⁰K^- and K_S⁰K^- decay modes for D_s^(*) reconstruction and measure the following branching fractions: B(B⁺→D_s^-K⁺π⁺)=(1.71_-0.07^+0.08(stat)_-0.20^+0.20(syst)±0.15(B_int))×10^-4 and B(B⁺→D_s^*-K⁺π⁺)=(1.31_-0.12^+0.13(stat)_-0.25^+0.25(syst)±0.12(B_int))×10^-4. The uncertainties are due to statistics, experimental systematic errors, and uncertainties of intermediate branching fractions, respectively.

In this study, molecular-dynamics simulations were employed with an embedded-atom method to investigate the shock-induced breaking behavior of single-crystal copper nanowires along a [100] direction at a constant strain rate. The cross section was fixed at 1.8 nm² for all model nanowires. The results showed that the final breaking position depended on the nanowire length. When it was less than 6.0 nm, the most probable breaking position was located at the center of the nanowires. However, it gradually shifted to the ends as the nanowire length increased over 6.0 nm. The longitudinal wave theory was used to interpret the shift of the most probable breaking position.

We report measurements of charmless hadronic B⁰ decays into the π⁺π^-K⁺π^- final state. The analysis uses a sample of 657×10⁶ BB̅ pairs collected with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider at the resonance. The decay B⁰→ρ⁰K⁺π^- is observed for the first time; the significance is 5.0σ and the corresponding partial branching fraction for M_Kπ∈(0.75,1.20)  GeV/c² is [2.8±0.5(stat)±0.5(syst)]×10^-6. We also obtain the first evidence for B⁰→f₀(980)K⁺π^- with 3.5σ significance and for B⁰→π⁺π^-K^*0 with 4.5σ significance. For the two-body decays B⁰→ρ⁰K^*0 and B⁰→f₀(980)K^*0, the significances are 2.7σ and 2.5σ, respectively, and the upper limits on the branching fractions are 3.4×10^-6 and 2.2×10^-6 at 90% confidence level.

A low-frequency (<4  kHz), poloidally and toroidally symmetrical potential structure that peaks near zero frequency is observed in the edge plasma of the HL-2A tokamak. The axisymmetry structure exhibits a radial coherence length less than 1 cm. These characteristics are consistent with the theoretically predicted low-frequency zonal flows (LFZF). The radial wave-number frequency spectra of the LFZF show that the LFZF packets propagate both outwards and inwards. The geodesic acoustic mode (GAM) is found to coexist with the LFZF, and the LFZF is found to modulate the GAM and ambient turbulence with in-phase and antiphase relations, respectively, through an envelope analysis.

We report observation of the electroweak production of single top quarks in pp̅ collisions at sqrt[s]=1.96  TeV based on 2.3  fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of σ(pp̅ →tb+X,tqb+X)=3.94±0.88  pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5×10^-7, corresponding to a 5.0 standard deviation significance for the observation.

We search for a new light gauge boson, a dark photon, with the D0 experiment. In the model we consider, supersymmetric partners are pair produced and cascade to the lightest neutralinos that can decay into the hidden sector state plus either a photon or a dark photon. The dark photon decays through its mixing with a photon into fermion pairs. We therefore investigate a previously unexplored final state that contains a photon, two spatially close leptons, and large missing transverse energy. We do not observe any evidence for dark photons and set a limit on their production.

Using high statistics samples of charged-current ν_μ interactions, the MiniNooNE Collaboration reports a measurement of the single-charged-pion production to quasielastic cross section ratio on mineral oil (CH₂), both with and without corrections for hadron reinteractions in the target nucleus. The result is provided as a function of neutrino energy in the range 0.4  GeV<E_ν<2.4  GeV with 11% precision in the region of highest statistics. The results are consistent with previous measurements and the prediction from historical neutrino calculations.

We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a bb̅ 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.

We report a universal scaling law, τ_y=3R(T_g-RT)/V, that uncovers an inherent relationship of the yield strength τ_y with the glass transition temperature T_g and molar volume V of metallic glasses. This equation is derived from fundamental thermodynamics and validated by various metallic glasses with well-defined yielding. The linearity between τ_y and T_g demonstrates the intrinsic correlation between yielding and glass-liquid transition, which contributes to the basic understanding of the strength and deformation of glassy alloys.

From a Dalitz plot analysis of B→Kπ⁺ψ^′ decays, we find a signal for Z(4430)⁺→π⁺ψ^′ with a mass M=(4443_-12-13⁺¹⁵⁺¹⁹)  MeV/c², width Γ=(107_-43-56⁺⁸⁶⁺⁷⁴)  MeV, product branching fraction B(B̅ ⁰→K^-Z(4430)⁺)×B(Z(4430)⁺→π⁺ψ^′)=(3.2_-0.9-1.6^+1.8+5.3)×10^-5, and significance of 6.4σ that agrees with previous Belle measurements based on the same data sample. In addition, we determine the branching fraction B(B⁰→K^*(892)⁰ψ^′)=(5.52_-0.32-0.58^+0.35+0.53)×10^-4 and the fraction of K^*(892)⁰ mesons that are longitudinally polarized f_L=(44.8_-2.7-5.3^+4.0+4.0)%. 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.

The MiniBooNE Collaboration reports a search for ν_μ and ν̅ _μ disappearance in the Δm² region of 0.5–40  eV². These measurements are important for constraining models with extra types of neutrinos, extra dimensions, and CPT violation. Fits to the shape of the ν_μ and ν̅ _μ energy spectra reveal no evidence for disappearance at the 90% confidence level (C.L.) in either mode. The test of ν̅ _μ disappearance probes a region below Δm²=40  eV² never explored before.

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 μ⁺μ^- or one to μ⁺μ^- and the other to τ⁺τ^-. No significant signal is observed, and we set limits on its production as functions of M_a and M_h.

We report electrical and magnetotransport measurements on La₄Ru₆O₁₉ that was found previously to feature metal-metal bonding and non-Fermi-liquid behavior. Our measurements showed that the transverse and longitudinal magnetoresistance grew rapidly below 30 K. Moreover, the longitudinal magnetoresistance is larger than the transverse magnetoresistance measured at the same temperatures (T) and the sign of the magnetoresistance is negative, suggesting the presence of ferromagnetic fluctuations in La₄Ru₆O₁₉. However, as T was lowered further to below T^∗=4 K, the magnetoresistance was found to change its sign from negative to positive. The Hall coefficient, which is negative and strongly temperature dependent, reaches a maximum in its absolute value near T^∗. Most importantly, the resistivity ρ was found to follow the non-Fermi-liquid dependence of ρ∼T^3/2 below T^∗ in zero magnetic field and the Fermi-liquid behavior ρ∼T² in a high magnetic field. We suggest that these observations can be explained by the existence of ferromagnetic quantum criticality in La₄Ru₆O₁₉ near ambient pressure.

Phase interactions among signals of physical and physiological systems can provide useful information about the underlying control mechanisms of the systems. Physical and biological recordings are often noisy and exhibit nonstationarities that can affect the estimation of phase interactions. We systematically studied effects of nonstationarities on two phase analyses including (i) the widely used transfer function analysis (TFA) that is based on Fourier decomposition and (ii) the recently proposed multimodal pressure flow (MMPF) analysis that is based on Hilbert-Huang transform (HHT)—an advanced nonlinear decomposition algorithm. We considered three types of nonstationarities that are often presented in physical and physiological signals: (i) missing segments of data, (ii) linear and step-function trends embedded in data, and (iii) multiple chaotic oscillatory components at different frequencies in data. By generating two coupled oscillatory signals with an assigned phase shift, we quantify the change in the estimated phase shift after imposing artificial nonstationarities into the oscillatory signals. We found that all three types of nonstationarities affect the performances of the Fourier-based and the HHT-based phase analyses, introducing bias and random errors in the estimation of the phase shift between two oscillatory signals. We also provided examples of nonstationarities in real physiological data (cerebral blood flow and blood pressure) and showed how nonstationarities can complicate result interpretation. Furthermore, we propose certain strategies that can be implemented in the TFA and the MMPF methods to reduce the effects of nonstationarities, thus improving the performances of the two methods.

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 pp̅ collider. We select two final states: τ^± plus missing transverse energy and b jets, and τ⁺τ^- 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.