Search Results (26 total)

We present a new measurement of the difference between the nucleon strange and antistrange quark distributions from dimuon events recorded by the NuTeV experiment at Fermilab. This analysis is the first to use a complete next to leading order QCD description of charm production from neutrino scattering. Dimuon events in neutrino deep inelastic scattering allow direct and independent study of the strange and antistrange content of the nucleon. We find a positive strange asymmetry with a significance of 1.6σ. We also report a new measurement of the charm mass.

The NuTeV experiment at Fermilab has obtained a unique high-statistics sample of neutrino and antineutrino interactions using its high-energy sign-selected beam. We present a measurement of the differential cross section for charged-current neutrino and antineutrino scattering from iron. We determine the relative ν̅ to ν cross section, r=σ^ν̅ /σ^ν, at high energy with errors a factor of 2 smaller than the previous world average. Structure functions, F₂(x,Q²) and xF₃(x,Q²), are determined by fitting the inelasticity, y, dependence of the cross sections. This measurement has significantly improved systematic precision as a consequence of more precise understanding of hadron and muon energy scales.

The NuTeV Collaboration recently reported a value of sin²θ_W measured in neutrino-nucleon scattering that is 3 standard deviations above the standard model prediction. This result is derived assuming that (1) the strange sea is quark-antiquark symmetric, s(x)=s̅ (x), and (2) up and down quark distributions are symmetric under the simultaneous interchange of u↔d and p↔n. We report the impact of violations of these symmetries on sin²θ_W and discuss the theoretical and experimental constraints on such asymmetries.

Limits on ν_μ→ν_e and ν̅ _μ→ν̅ _e oscillations are extracted using the NuTeV detector with sign-selected ν_μ and ν̅ _μ beams. In ν̅ _μ mode, for the case of sin²2α  =  1, Δm²>2.6  eV² is excluded, and for Δm²≫1000 eV², sin²2α>1.1×10^-3. The NuTeV data exclude the high Δm² end of ν̅ _μ→ν̅ _e oscillation parameters favored by the LSND experiment without the need to assume that the oscillation parameters for ν and ν̅ are the same. We present the most stringent experimental limits for ν_μ(ν̅ _μ)→ν_e(ν̅ _e) oscillations in the large Δm² region.

Experimental analyses of charged current deep inelastic charm production—as observed through dimuon events in neutrino-iron scattering—measure the strangeness component of the nucleon sea. A complete analysis requires a Monte Carlo simulation to account for experimental detector acceptance effects; therefore, a fully differential theoretical calculation is necessary to provide complete kinematic information. We investigate the theoretical issues involved in calculating these differential distributions at next-leading order (NLO). Numerical results are presented for typical fixed-target kinematics. We present a corresponding FORTRAN code suitable for experimental NLO analysis.

The NuTeV Collaboration has extracted the electroweak parameter sin²θ_W from the measurement of the ratios of neutral current to charged current ν and ν̅ cross sections. Our value, sin²θ_W^(on-shell)  =  0.2277±0.0013(stat)±0.0009(syst), is 3 standard deviations above the standard model prediction. We also present a model independent analysis of the same data in terms of neutral-current quark couplings.

We report on the extraction of R  =  σ_L / σ_T from CCFR ν_μ-Fe and ν̅ _μ-Fe differential cross sections. The CCFR differential cross sections do not show the deviations from the QCD expectations that are seen in the CDHSW data at very low and very high x. R as measured in ν_μ scattering is in agreement with R as measured in muon and electron scattering. All data on R for Q²>1 GeV² are in agreement with a NNLO QCD calculation which uses NNLO parton distribution functions and includes target mass effects. We report on the first measurements of R in the low x and Q²<1 GeV² region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES Collaboration).

We present measurements of the semi-inclusive cross sections for ν_μ- and ν̅ _μ-nucleon deep inelastic scattering interactions with two oppositely charged muons in the final state. These events dominantly arise from the production of a charm quark during the scattering process. The measurement was obtained from the analysis of 5102 ν_μ-induced and 1458 ν̅ _μ-induced events collected with the NuTeV detector exposed to a sign-selected beam at the Fermilab Tevatron. We also extract a cross-section measurement from a reanalysis of 5030 ν_μ-induced and 1060 ν̅ _μ-induced events collected from the exposure of the same detector to a quad-triplet beam by the Chicago Columbia Fermilab Rochester (CCFR) experiment. The results are combined to obtain the most statistically precise measurement of neutrino-induced dimuon production cross sections to date. These measurements should be of broad use to phenomenologists interested in the dynamics of charm production, the strangeness content of the nucleon, and the Cabibbo-Kobayashi-Maskawa matrix element V_cd.

The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to perform a search for the lepton number violating process ν̅ _μe^-→μ^-ν̅ _e, and to measure the cross section of the standard model inverse muon decay process ν_μe^-→μ^-ν_e. NuTeV measures the inverse muon decay asymptotic cross-section slope σ/E to be (13.8±1.2±1.4)×10^-42 cm²/GeV. The experiment also observes no evidence for lepton number violation and places one of the most restrictive limits on the cross-section ratio σ(ν̅ _μe^-→μ^-ν̅ _e)/σ(ν_μe^-→μ^-ν_e)≤1.7% at 90% C.L. for V-A couplings and ≤0.6% for scalar couplings.

A search for long-lived neutral particles ( N⁰’s) with masses above 2.2 GeV/c² that decay into at least one muon has been performed using an instrumented decay channel at the NuTeV experiment at Fermilab. Data were examined for particles decaying into the final states μμ, μe, and μπ. Three μμ events were observed over an expected standard model background of 0.069±0.010 events; no events were observed in the other modes.

A new structure function analysis of CCFR deep inelastic ν-N and ν̅ -N scattering data is presented for previously unexplored kinematic regions down to Bjorken x  =  0.0045 and Q²  =  0.3 GeV². Comparisons to charged lepton scattering data from NMC and E665 experiments are made and the behavior of the structure function F₂^ν is studied in the limit Q²→0.

We report on the first observation of open charm production in neutral current deep inelastic neutrino scattering as seen in the NuTeV detector at Fermilab. The production rate is shown to be consistent with a pure gluon-Z⁰ boson production model, and the observed level of charm production is used to determine the effective charm mass. As part of our analysis, we also obtain a new measurement for the proton-nucleon charm production cross section at sqrt[s]=38.8 GeV.

We report on the extraction of the structure functions F₂ and ΔxF₃  =  xF₃^ν-xF₃^ν̅ from CCFR ν_μ-Fe and ν̅ _μ-Fe differential cross sections. The extraction is performed in a physics model-independent (PMI) way. This first measurement of ΔxF₃, which is useful in testing models of heavy charm production, is higher than current theoretical predictions. The ratio of the F₂ (PMI) values measured in ν_μ and μ scattering is in agreement (within 5%) with the predictions of next-to-leading-order parton distribution functions using massive charm production schemes, thus resolving the long-standing discrepancy between the two sets of data.

We report on a search for flavor-changing neutral-currents (FCNC) in the production of heavy quarks in deep inelastic ν_μN and ν̅ _μN scattering by the NuTeV experiment at the Fermilab Tevatron. This measurement, made possible by the high-purity NuTeV sign-selected beams, probes for FCNC in heavy flavors at the quark level, and is uniquely sensitive to neutrino couplings of potential FCNC mediators. All searches are consistent with zero, and limits on the effective mixing strengths |V_uc|², |V_db|², and |V_sb|² are obtained.

The E815 (NuTeV) neutrino experiment has performed a search for a 33.9 MeV/c² weakly interacting neutral particle produced in pion decay. Such a particle may be responsible for an anomaly in the timing distribution of neutrino interactions in the KARMEN experiment. E815 has searched for this particle's decays in an instrumented decay region; no evidence for this particle was found. The search is sensitive to pion branching ratios as low as 10^-13.

We present evidence for the diffractive processes ν_μFe→μ^-D_S⁺(D_S^*)Fe and ν̅ _μFe→μ⁺D_S^-(D_S^*)Fe using the Fermilab SSQT neutrino beam and the Lab E neutrino detector. The data are consistent with standard model production of the neutrino trident reactions ν_μFe→ν_μμ^-μ⁺Fe and ν̅ _μFe→ν̅ _μμ⁺μ^-Fe. We see no evidence for neutral-current production of J/ψ via either diffractive or deep inelastic scattering mechanisms.

A search for neutral heavy leptons (NHLs) has been performed using an instrumented decay channel at the NuTeV (E-815) experiment at Fermilab. The data were examined for NHLs decaying into muonic final states ( μμν, μeν, μπ, and μρ); no evidence has been found for NHLs in the 0.25–2.0 GeV mass range. This analysis places limits on the mixing of NHLs with standard light neutrinos at a level up to an order of magnitude more restrictive than previous search limits in this mass range.

A speed-adjustment car-following model is extended to systems of traffic where there is a variety of vehicle response times and speed-headway relationships. This is proposed as a model of the interactions between cars and trucks on single-lane roads where there is no overtaking, and some of its properties are derived. First, we make a distinction between temporal stability on a circular road and spatial stability on a straight road and go on to derive criteria for linear stability in each case. The propagation and dispersion of a linear disturbance wave is studied, and we also compare the nonlinear evolution of both single- and multiple-species systems on circuitous and straight roads. When the speed-headway relationship of all vehicles is given by the nonlinear law proposed by Bando et al. [Phys. Rev. E 51, 2 (1995)], we find that for models of car-truck systems, as for systems consisting of one type of vehicle only, there is a range of equilibrium headways for which the system is linearly unstable. The size of this range increases with the proportion of the more unreactive vehicle type, trucks, in the population of vehicles. Computer simulations verify the analytical results and show the nonlinear development of disturbances when the system is linearly unstable. It is demonstrated that slow vehicles in a platoon moving at close to their top speed can damp nonlinear congestion waves.

Proton-proton bremsstrahlung cross sections were measured for final-state proton angles of (20°, 20°), (20°, 26°), (23°, 30°), (25°, 25°), (25°, 35°), (26°, 35°), (26.5°, 26.5°), and (30°, 30°). Differential cross sections as a function of γ-ray angle were extracted from four sets of data. A theoretical prediction of the (30°, 30°) angular distribution, averaged over the azimuthal acceptance of the counters, agrees well with the experimental result. Total cross sections were obtained at all pairs of angles mentioned and were used to estimate the coplanar cross sections. The coplanar cross sections agree with results of a model-independent soft-photon calculation. They are smaller than predictions made with either a hard-core potential or a momentum-dependent potential, but they favor the latter.

The cross section for proton-proton bremsstrahlung at 47 MeV was measured by detecting the two protons at 30° on either side of the beam. Strongly noncoplanar events were not accepted. The integrated cross section and differential cross section as a function of γ-ray polar angle are in reasonable agreement with recent theoretical predictions. A survey of all presently available (30°, 30°) measurements and predictions is given.

The two final-state protons in the reaction p+p→p+p+γ at 61.7±0.1 MeV were detected by (ΔE, E) telescopes placed at 30° on opposite sides of the beam. About 250 events were detected in a geometry with angular acceptance comparable to the maximum possible noncoplanarity. Additional data were obtained with apertures of smaller height, restricting the measurement to a more nearly coplanar geometry. The data indicate that the cross section is smaller for noncoplanar events. The estimated coplanar cross sections and differential cross section as a function of γ-ray angle are presented. The results agree with recent theoretical predictions.

Measurements have been made of the spin-lattice relaxation times at 35 GHz on specimens of ruby grown from the vapor phase with chromium concentrations from 0.002 to 0.2%. Correlation of these results with x-ray data has shown that in the one-phonon region the relaxation times at 4.2°K depend on the total undulation of the lattice planes within the specimen and that this effect is temperature-dependent. Thus, the magnitude of the relaxation time can be affected by a factor of 2 in typical specimens. The temperature dependence of the relaxation times in the Raman region can be explained using the theory of Castle et al., if two defect sites are assumed. Comparable results are presented for rubies grown by the Verneuil and Czochralski methods.