Search Results (82 total)

We search Hubble Space Telescope Treasury Program images collected as part of the Great Observatories Origins Deep Survey for pairs of galaxies consistent with the gravitational lensing signature of a cosmic string. Our technique includes estimates of the efficiency for finding the lensed galaxy pair. In the north (south) survey field we find no evidence out to a redshift of greater than 0.5 (0.3) for cosmic strings to a mass per unit length limit of Gμ/c²<3.0×10^-7 at 95% confidence limits (C.L.). In the combined 314.9  arcmin² of the north and south survey fields this corresponds to a global limit on Ω_strings<0.02. Our limit on Gμ/c² is more than an order of magnitude lower than searches for individual strings in cosmic microwave background (CMB) data. Our limit is higher than other CMB and gravitational wave searches, however, we note that it is less model dependent than these other searches.

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 Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or two-neutron intranuclear disappearance that would produce holes in the s-shell energy level of ¹²C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n→3ν or nn→2ν. The deexcitation of the corresponding daughter nucleus results in a sequence of space and time-correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: τ(n→inv)>5.8×10²⁹ years and τ(nn→inv)>1.4×10³⁰ years at 90% C.L. These results represent an improvement of factors of ∼3 and >10⁴ over previous experiments.

We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 ν̅ _e candidate events with energies above 3.4 MeV compared to 365.2±23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8±7.3 expected background events, the statistical significance for reactor ν̅ _e disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from ν̅ _e oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Δm²=7.9_-0.5^+0.6×10^-5  eV². A global analysis of data from KamLAND and solar-neutrino experiments yields Δm²=7.9_-0.5^+0.6×10^-5  eV² and tan⁡²θ=0.40_-0.07^+0.10, the most precise determination to date.

Data corresponding to a KamLAND detector exposure of 0.28 kton yr has been used to search for ν̅ _e’s in the energy range 8.3<E_{ν̅ e}<14.8  MeV. No candidates were found for an expected background of 1.1±0.4 events. This result can be used to obtain a limit on ν̅ _e fluxes of any origin. Assuming that all ν̅ _e flux has its origin in the Sun and has the characteristic ⁸B solar ν_e energy spectrum, we obtain an upper limit of 3.7×10²  cm^-2 s^-1 (90% C.L.) on the ν̅ _e flux. We interpret this limit, corresponding to 2.8×10^-4 of the standard solar model ⁸B ν_e flux, in the framework of spin-flavor precession and neutrino decay models.

KamLAND has measured the flux of ν̅ _e’s from distant nuclear reactors. We find fewer ν̅ _e events than expected from standard assumptions about ν̅ _e propagation at the 99.95% C.L. In a 162   ton·yr exposure the ratio of the observed inverse β-decay events to the expected number without ν̅ _e disappearance is 0.611±0.085(stat)±0.041(syst) for ν̅ _e energies >3.4  MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the “large mixing angle” region are excluded.

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.

A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are ²⁹Si nuclear spins arranged as chains in a ²⁸Si (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for ensemble measurement.

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.

We report experiments on resonant tunneling of charge e/3 quasiparticles through states bound on a quantum antidot. We find that at a given temperature T the line shape of resonances fits predictions of Fermi and Luttinger liquid theories equally well, the difference between the theoretical line shapes being well within 1%. As T is varied, the experimental resonances scale linearly with T, as expected for both Fermi and Luttinger tunneling for quasiparticles, and not as T^2/3 predicted by the Luttinger theory for electrons.