Search Results (24 total)

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 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 status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].

We report measurements of the ratios K⁺ / π⁺, p / π⁺, K^- / π^-, p̅ / π^-, π^- / π⁺, K^- / K⁺, and p̅ / p for hadrons with 0.19<x_t<0.62 produced in p-Be and p-W collisions at sqrt[s]=38.8 GeV. The K⁺ / π⁺ ratio at high x_t gives the fragmentation-function ratio D_u^K+ / D_u^π+ at high z. The high-x_t K^- / π^- ratio gives an upper limit for D_d^K- / D_d^π- at high z. The p_t dependence of p / π⁺ suggests that scattered constituent diquarks are the primary source of protons with p_t<6 GeV/c. We also present species correlations in high-mass h⁺ / h^- pairs. Strong K⁺ / K^- and pp̅ correlations were observed.

We present a high-statistics, species-identified measurement of the W-to-Be per-nucleon cross-section ratio, R_W/Be, for high-x_t hadrons and high-τ h⁺h^- pairs produced in p-A collisions at √s =38.8 GeV. The data extend to 0.62 in x_t and 0.39 in √τ . For single hadrons, R_W/Be peaks at p_t≊5 GeV/c and decreases to ≊1 for mesons with pt>8 GeV/c. At fixed p_t, R_W/Be falls with √s . For symmetric pairs with √τ >0.28, R_W/Be=0.84±0.02±0.07, suggesting a nuclear suppression of high-z fragmentation. R_W/Be increases with p_out, indicative of constituent multiple scattering.

Results of high-transverse-momentum charged-hadron production in 400-GeV/c proton-proton and proton-deuteron collisions and 800-GeV/c proton-proton collisions are presented. The transverse-momentum range of the data is from 5.2 to 9.0 GeV/c for the 400-GeV/c collisions and from 3.6 to 11.0 GeV/c for the 800-GeV/c collisions; the data are centered around 90° in the proton-nucleon center-of-momentum system. Single-pion invariant cross sections and particle ratios were measured at both energies. The results are compared to previous experiments and the Lund model.

The hadronic production of dielectrons in the Υ region has been measured with a mass resolution of 0.17% using incident protons with momentum of 800 GeV/c. The cross sections of the Υ resonances are compared with the predictions of a gluon-fusion model. The dielectron continuum is also compared with the Drell-Yan prediction, and the K factor is extracted. The results on the mean transverse momentum of the resonances and that of the continuum are also presented.

Measurements of correlations of nearly back-to-back hadrons produced at a large transverse momentum in sqrt[s]=38.8 GeV proton-proton collisions are presented and compared to previous results with a beryllium target. The correlations of identified unlike-sign hadron pairs in ratio to the correlation for all unlike-sign pairs are compared with predictions of the Lund model. These predictions differ from the data.

We present results on the production of hadrons in collisions of 400-GeV/c protons with beryllium, copper, and tungsten nuclei. The data cover the region from 5.6 to 8.0 GeV/c in the transverse momentum of the final-state hadron and from 73° to 102° in the proton-nucleon center-of-momentum frame production angle theta^*. The restriction of the data to values of x_T (x_T=2p_T/ √s ) greater than 0.4 enriches the sample with hard collisions of valence quarks. Asymmetries about theta^*=90° reflect the presence of neutrons in the target nuclei. The variation of the atomic-weight dependence parameter α with production angle is discussed in the context of the phenomenology of nucleonic structure within nuclei. We also extrapolate our measurements to a ‘‘deuteron’’ target to minimize nuclear effects and compare the result to QCD calculations.

A search for neutral penetrating particles has been made by use of an 800-GeV proton beam incident on the magnetized beam dump of the spectrometer of Fermilab experiment 605. Limits on the mass and couplings of such particles are presented. A 1.8-MeV axion coupled only to e⁺e^- is ruled out.

We present new data on the A dependence of the inclusive production of high–transverse-momentum hadrons, both singles and symmetric pairs. These data qualitatively support the hypothesis that the observed A dependence results from multiple scattering of quarks and gluons within the target nucleus.

We have established a sensitive upper limit on φφ resonance production by 350-GeV/c protons incident on a beryllium target. The 90%-confidence-level upper limit varies from 1.5×10^-30 cm²/nucleon at M_φφ=2.8 GeV/c² to 6.0×10^-32 cm²/nucleon at M_φφ=3.4 GeV/c². We observe no evidence of the η_c.

We have measured the nucleon-number (A) dependence of hadron-pair production in 400-GeV/c proton-nucleus collisions, using Pb and Be targets. Charged-hadron pairs were observed near rapidity y_c.m.=-0.4 with Δϕ≅180°. The A-dependence exponent rises from 1.1 to 1.2 in the range 2.0<~|p_⊥1|+|p_⊥2|<~4.5 GeV/c. The dihadron p_⊥ correlation function is significantly smaller for Pb than for Be.

We have measured two-particle quantum-number correlations in 400-GeV/c proton-nucleus collisions. A double-arm spectrometer was used to detect two charged particles produced near rapidity y_c.m.=-0.4 in the proton-nucleon center-of-mass system. In proton-beryllium collisions we observe positive pp̅ and K⁺K^- correlations which are independent of the transverse momenta of the particles over the range 1<~p_⊥<~1.8 GeV/c. These correlations are weaker in proton-lead interactions.

We have measured the invariant cross section for inclusive ϕ production in proton-nucleus collisions at 400 GeV/c near Feynman x=0. For transverse momenta in the range between 0.8 and 3.5 GeV/c the ratio of ϕ to π^- rises from 1 to 7%. We also report on correlations with particles opposite the ϕ in the center-of-mass system as they relate to the Okubo-Zweig-Iizuka rule.

We have searched for the charmed and other new particles by measuring the hadron pair mass spectra in proton-nucleus collisions at 400 GeV/c. Results are presented for π^-K⁺, π⁺K^-, and π⁺π^- pairs in the mass region from 1.5 to 4.0 GeV/c². No evidence for narrow resonances was found. The sensitivity of the search varied from 2 × 10^-30 cm² at 2 GeV/c² to 5 × 10^-32 cm² at 4 GeV/c². Experimental checks were provided by the observation of a clean J / ψ(3.1)→μ⁺μ^- signal.