Search Results (29 total)

This paper examines sterile neutrino oscillation models in light of recently published results from the MiniBooNE Experiment. The new MiniBooNE data include the updated neutrino results, including the low-energy region, and the first antineutrino results, as well as first results from the off-axis NuMI beam observed in the MiniBooNE detector. These new global fits also include data from LSND, KARMEN, NOMAD, Bugey, CHOOZ, CCFR84, and CDHS. Constraints from atmospheric oscillation data have been imposed. We test the validity of the three-active plus one-sterile (3+1) and two-sterile (3+2) oscillation hypotheses, and we estimate the allowed range of fundamental neutrino oscillation parameters in each case. We assume CPT-invariance throughout. However, in the case of (3+2) oscillations, CP violation is allowed. We find that, with the addition of the new MiniBooNE data sets, a (3+2) oscillation hypothesis provides only a marginally better description of all short-baseline data over a (3+1) oscillation hypothesis. In the case of (3+2) CP-violating models, we obtain good χ²-probabilities in general due to the large number of fit parameters. However, we find large incompatibilities among appearance and disappearance experiments, consistent with previous analyses. Aside from LSND, the data sets responsible for this tension are the MiniBooNE neutrino data set, CDHS, and the atmospheric constraints. In addition, new incompatibilities are found between the appearance experiments themselves (MiniBooNE, LSND, KARMEN and NOMAD), independent of CP-violation assumptions. On the other hand, fits to antineutrino-only data sets, including appearance and disappearance experiments, are found significantly more compatible, even within a (3+1) oscillation scenario.

The MiniBooNE Collaboration reports initial results from a search for ν̅ _μ→ν̅ _e oscillations. A signal-blind analysis was performed using a data sample corresponding to 3.39×10²⁰ protons on target. The data are consistent with background prediction across the full range of neutrino energy reconstructed assuming quasielastic scattering, 200<E_ν^QE<3000  MeV: 144 electronlike events have been observed in this energy range, compared to an expectation of 139.2±17.6 events. No significant excess of events has been observed, both at low energy, 200–475 MeV, and at high energy, 475–1250 MeV. The data are inconclusive with respect to antineutrino oscillations suggested by data from the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory.

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.

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 the first observation of off-axis neutrino interactions in the MiniBooNE detector from the NuMI beam line at Fermilab. The MiniBooNE detector is located 745 m from the NuMI production target, at 110 mrad angle (6.3°) with respect to the NuMI beam axis. Samples of charged-current quasielastic ν_μ and ν_e interactions are analyzed and found to be in agreement with expectation. This provides a direct verification of the expected pion and kaon contributions to the neutrino flux and validates the modeling of the NuMI off-axis beam.

The booster neutrino experiment (MiniBooNE) searches for ν_μ→ν_e oscillations using the O(1  GeV) neutrino beam produced by the booster synchrotron at the Fermi National Accelerator Laboratory). The booster delivers protons with 8 GeV kinetic energy (8.89  GeV/c momentum) to a beryllium target, producing neutrinos from the decay of secondary particles in the beam line. We describe the Monte Carlo simulation methods used to estimate the flux of neutrinos from the beam line incident on the MiniBooNE detector for both polarities of the focusing horn. The simulation uses the Geant4 framework for propagating particles, accounting for electromagnetic processes and hadronic interactions in the beam line materials, as well as the decay of particles. The absolute double differential cross sections of pion and kaon production in the simulation have been tuned to match external measurements, as have the hadronic cross sections for nucleons and pions. The statistical precision of the flux predictions is enhanced through reweighting and resampling techniques. Systematic errors in the flux estimation have been determined by varying parameters within their uncertainties, accounting for correlations where appropriate.

The MiniBooNE Collaboration observes unexplained electronlike events in the reconstructed neutrino energy range from 200 to 475 MeV. With 6.46×10²⁰ protons on target, 544 electronlike events are observed in this energy range, compared to an expectation of 415.2±43.4 events, corresponding to an excess of 128.8±20.4±38.3 events. The shape of the excess in several kinematic variables is consistent with being due to either ν_e and ν̅ _e charged-current scattering or ν_μ neutral-current scattering with a photon in the final state. No significant excess of events is observed in the reconstructed neutrino energy range from 475 to 1250 MeV, where 408 events are observed compared to an expectation of 385.9±35.7 events.

The SciBooNE Collaboration has performed a search for charged current coherent pion production from muon neutrinos scattering on carbon, ν_μ¹²C→μ^-12Cπ⁺, with two distinct data samples. No evidence for coherent pion production is observed. We set 90% confidence level upper limits on the cross section ratio of charged current coherent pion production to the total charged current cross section at 0.67×10^-2 at mean neutrino energy 1.1 GeV and 1.36×10^-2 at mean neutrino energy 2.2 GeV.

This article presents the compatibility of experimental data from neutrino oscillation experiments with a high-Δm² two-neutrino oscillation hypothesis. Data is provided by the Bugey, Karlsruhe Rutherford Medium Energy Neutrino Experiment 2 (KARMEN2), Los Alamos Liquid Scintillator Neutrino Detector (LSND), and MiniBooNE experiments. The LSND, KARMEN2, and MiniBooNE results are 25.36% compatible within a two-neutrino oscillation hypothesis. However, the point of maximal compatibility is found in a region that is excluded by the Bugey data. A joint analysis of all four experiments, performed in the sin⁡²2θ vs Δm² region common to all data, finds a maximal compatibility of 3.94%. This result does not account for additions to the neutrino oscillation model from sources such as CP violation or sterile neutrinos.

The observation of neutrino oscillations is clear evidence for physics beyond the standard model. To make precise measurements of this phenomenon, neutrino oscillation experiments, including MiniBooNE, require an accurate description of neutrino charged current quasielastic (CCQE) cross sections to predict signal samples. Using a high-statistics sample of ν_μ CCQE events, MiniBooNE finds that a simple Fermi gas model, with appropriate adjustments, accurately characterizes the CCQE events observed in a carbon-based detector. The extracted parameters include an effective axial mass, M_A^eff=1.23±0.20  GeV, that describes the four-momentum dependence of the axial-vector form factor of the nucleon, and a Pauli-suppression parameter, κ=1.019±0.011. Such a modified Fermi gas model may also be used by future accelerator-based experiments measuring neutrino oscillations on nuclear targets.

The MiniBooNE Collaboration reports first results of a search for ν_e appearance in a ν_μ beam. With two largely independent analyses, we observe no significant excess of events above the background for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two-neutrino appearance-only oscillation model.

We investigate the extent to which leptonic CP-violation in (3+2) sterile neutrino models leads to different oscillation probabilities for ν̅ _μ→ν̅ _e and ν_μ→ν_e oscillations at MiniBooNE. We are using a combined analysis of short-baseline (SBL) oscillation results, including the LSND and null SBL results, to which we impose additional constraints from atmospheric oscillation data. We obtain the favored regions in MiniBooNE oscillation probability space for both (3+2) CP-conserving and (3+2) CP-violating models. We further investigate the allowed CP-violation phase values and the MiniBooNE reach for such a CP violation measurement. The analysis shows that the oscillation probabilities in MiniBooNE neutrino and antineutrino running modes can differ significantly, with the latter possibly being as much as 3 times larger than the first. In addition, we also show that all possible values of the single CP-violation phase measurable at short baselines in (3+2) models are allowed within 99% CL by existing data.

The sin⁡²θ_W result from NuTeV falls three standard deviations from the value determined by global electroweak fits. It has been suggested that one possible explanation for this result could be the oscillation of electron neutrinos in the NuTeV beam to sterile neutrinos. This article examines several cases of masses and mixings for 3+2 neutrino oscillation models which fit the current oscillation data at 99% C.L. We conclude that electron to sterile neutrino oscillations can account for only up to a third of a standard deviation between the NuTeV determination of sin⁡²θ_W and the standard model.

This paper presents a strategy for measuring sin⁡²θ_W to ∼1% at a reactor-based experiment, using ν̅ e elastic scattering. This error is comparable to the NuTeV, SLAC E158, and atomic parity violation results on sin⁡²θ_W, but with substantially different systematic contributions. The measurement can be performed using the near detector of the presently proposed reactor-based oscillation experiments. We conclude that an absolute error of ∼δ(sin²θ_W)=0.0019 may be achieved.

We investigate adding two sterile neutrinos to resolve the apparent tension existing between short-baseline neutrino oscillation results and CPT-conserving, four-neutrino oscillation models. For both (3+1) and (3+2) models, the level of statistical compatibility between the combined dataset from the null short-baseline experiments Bugey, CHOOZ, CCFR84, CDHS, KARMEN, and NOMAD, on the one hand; and the LSND dataset, on the other, is computed. A combined analysis of all seven short-baseline experiments, including LSND, is also performed, to obtain the favored regions in neutrino mass and mixing parameter space for both models. Finally, four statistical tests to compare the (3+1) and the (3+2) hypotheses are discussed. All tests show that (3+2) models fit the existing short-baseline data significantly better than (3+1) models.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

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.

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.

Neutrino-scattering measurements offer a unique tool for probing the electroweak and strong interactions as described by the standard model. Electroweak measurements are accessible through the comparison of neutrino neutral- and charged-current scattering. These measurements are complementary to other electroweak measurements due to differences in the radiative corrections both within and outside the standard model. Neutrino-scattering measurements also provide a precise method for measuring the F₂(x,Q²) and xF₃(x,Q²) structure functions. The predicted Q² evolution can be used to test perturbative quantum chromodynamics as well as to measure the strong-coupling constant α_s and the valence, sea, and gluon parton distributions. In addition, neutrino charm production, which can be determined from the observed dimuon events, allows the strange-quark sea to be investigated along with measurements of the CKM matrix element |V_cd| and the charm quark mass.

The proton and deuteron structure functions F₂^p and F₂^d are measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment E665 during 1991 and 1992 using liquid hydrogen and deuterium targets. The F₂ measurements are reported in the range 0.0008<x<0.6 and 0.2<Q²<75 GeV². These are the first precise measurements of F₂ in the low x and Q² range of the data. In the high x range of the data where they overlap in x and Q² with the measurements from NMC, the two measurements are in agreement. The E665 data also overlap in x with the DESY HERA data, and there is a smooth connection in Q² between the two data sets. At high Q² the E665 measurements are consistent with QCD-evolved leading twist structure function models. The data are qualitatively described by structure function models incorporating the hadronic nature of the photon at low Q². The Q² and the W dependence of the data measure the transition in the nature of the photon between a pointlike probe at high Q² and a hadronic object at low Q².

The ratio of the deuteron to proton structure functions is measured at very small Bjorken x (down to 10^–6) and for Q²>0.001 GeV² from scattering of 470 GeV muons on liquid hydrogen and deuterium targets. The ratio F₂ⁿ/F₂^p extracted from these measurements is found to be constant, at a value of 0.935±0.008±0.034, for x<0.01. This result suggests the presence of nuclear shadowing effects in the deuteron. The dependence of the ratio on Q² is also examined; no significant variation is found.

We detected 1–10 MeV neutrons at laboratory angles from 80° to 140° in coincidence with 470 GeV muons deep inelastically scattered from H, D, C, Ca, and Pb targets. The neutron energy spectrum for Pb can be fitted with two components with temperature parameters of 0.7 and 5.0 MeV. The average neutron multiplicity for 40<ν<400 GeV is about 5 for Pb, and less than 2 for Ca and C. These data are consistent with a process in which the emitted hadrons do not interact with the rest of the nucleus within distances smaller than the radius of Ca, but do interact within distances on the order of the radius of Pb in the measured kinematic range. For all targets the lack of high nuclear excitation is surprising.

Nuclear transparencies measured in exclusive incoherent ρ⁰ meson production from hydrogen, deuterium, carbon, calcium, and lead in muon-nucleus scattering are reported. The data were obtained with the E665 spectrometer using the Fermilab Tevatron muon beam with a mean beam energy of 470 GeV. Increases in the nuclear transparencies are observed as the virtuality of the photon increases, in qualitative agreement with the expectations of color transparency.

Fermilab Experiment-665 measured deep-inelastic scattering of 490 GeV muons off deuterium and xenon targets. Events were selected with a range of energy exchange ν from 100 GeV to 500 GeV and with large ranges of Q² and x_Bj: 0.1 GeV²/c²<Q²<150 GeV²/c² and 0.001<x_Bj<0.5. The fractional energy (z) distributions of forward-produced hadrons from the two targets have been compared as a function of the kinematics of the scattering; specifically, the kinematic region of ‘‘shadowing’’ has been compared to that of nonshadowing. The dependence of the distributions upon the order of the hadrons, determined by the fractional energies, has been examined as well; a strong degree of similarity has been observed in the shapes of the distributions of the different order hadrons. These z distributions, however, show no nuclear dependence, even in the kinematic region of shadowing.