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The MiniBooNE Collaboration reports first results of a search for [upsilon]{sub e} appearance in a [upsilon]{sub {mu}} beam. With two largely independent analyses, we observe no significant excess of events above background for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two neutrino appearance-only oscillation model.
The evidence is compelling that neutrinos undergo flavor change as they propagate. In recent years, experiments have observed this phenomenon of neutrino oscillations using disparate neutrino sources: the sun, fission reactors, accelerators, and secondary cosmic rays. The standard model of particle physics needs only simple extensions - neutrino masses and mixing - to accommodate all neutrino oscillation results to date, save one. The 3.8[sigma]-significant {bar {nu}}{sub e} excess reported by the LSND collaboration is consistent with {bar {nu}}{sub {mu}} →{bar {nu}}{sub e} oscillations with a mass-squared splitting of [Delta]m2 ≈ 1 eV2. This signal, which has not been independently verified, is inconsistent with other oscillation evidence unless more daring standard model extensions (e.g. sterile neutrinos) are considered.
Solar and atmospheric neutrino oscillations, recently confirmed by reactor and accelerator-based experiments, are now well established. On the other hand, the interpretation of the LSND {bar [nu]}{sub e} excess [1] as {bar [nu]}{sub {mu}} → {bar [nu]}{sub e} oscillations at the [Delta]m2 ≈ 1 eV2 scale lacked for many years experimental confirmation or refutation. The primary goal of the MiniBooNE experiment [2] is to address this anomaly in an unambiguous and independent way. The MiniBooNE flux is obtained via a high-intensity, conventional neutrino beam. Secondary hadrons, mostly pions and kaons, are produced via the interactions of 8 GeV protons from the Fermilab Booster accelerator with a thick beryllium target, and are focused by a horn. The switchable horn polarity allows for both neutrino and antineutrino running modes. The neutrino beam is produced via the decay of secondary mesons and muons in a 50 m long decay region. Overall, about 9.5 x 102° protons on target have been accumulated over the five years of beamline operation, 5.6 x 102° of which are used in this oscillation analysis, based on the neutrino running mode sample only. The MiniBooNE detector is located 540 m away from the beryllium target. The detector is a 12 m in diameter sphere filled with 800 t of undoped mineral oil, whose inner region is instrumented with 1280 photomultiplier tubes (PMTs). Neutrino interactions produce prompt, ring-distributed Cherenkov light, and delayed, isotropic scintillation light. Light transmission is affected by fluorescence, scattering, absorption and reflections. The outer detector region is used to reject cosmic ray activity or uncontained neutrino interactions. About 7.7 x 105 neutrino interactions have been collected at MiniBooNE. The goal of the first MiniBooNE electron appearance analysis is two-fold: perform a model-independent search for a {nu}{sub e} excess (or deficit), and interpret the data within a two neutrino, appearance-only {nu}{sub {mu}} → {nu}{sub e} oscillation context, to test this interpretation of the LSND anomaly [2]. This was a blind analysis.
An experiment is proposed to search concurrently for [nu]{sub [mu]} 2![nu]{sub e} and {bar [nu]}{sub {mu}} 2!{bar [nu]{sub e} oscillations with high sensitivity at LAMPF. The detector consists of a tank with 200 tons of dilute liquid scintillator with 850 10-in. photomultiplier tubes mounted on the inside tank covering 28% of the surface. Both Cerenkov light and scintillation light will be detected. The tank will reside inside the existing E645 veto shield and the experiment will make use of the present A6 beam-stop neutrino source. After two years of data collection, 90% confidence level limits on {bar [nu]{sub mu}}([nu]{sub {mu}}) 2!{bar [nu]}{sub e}([nu]{sub e}) mixing strengths of 2.7(2.7) × 10−4 can be obtained for all [Delta]m2> 1 eV2. Similarly, for maximal mixing the 90% C.L. limits on [Delta]m2 are 1.7(4.0) × 10−2. This experiment will, therefore, provide the world's best terrestrial limits on [nu]{sub {mu}} 2![nu]{sub e}} oscillations. Other physics to be obtained includes measurements of the charged current reactions [nu]{sub e}C 2!e−N and [nu]{sub {mu}}C 2!{mu}−N, of the inelastic neutral current reaction {nu}C 2!{nu}C* (15.11- MeV [gamma]), and a search for the rare decays [pi]° 2!{nu}{bar {nu}} and [eta] 2!{nu}{bar {nu}}.
The evidence is compelling that neutrinos undergo flavor change as they propagate. In recent years, experiments have observed this phenomenon of neutrino oscillations using disparate neutrino sources: the sun, fission reactors, accelerators, and secondary cosmic rays. The standard model of particle physics needs only simple extensions - neutrino masses and mixing - to accommodate all neutrino oscillation results to date, save one. The 3.8?-significant $ar{v}$e excess reported by the LSND collaboration is consistent with $ar{v}$? →$ar{v}$e oscillations with a mass-squared splitting of ?m2 ̃1 eV2. This signal, which has not been independently verified, is inconsistent with other oscillation evidence unless more daring standard model extensions (e.g. sterile neutrinos) are considered.
There is accumulating evidence for a difference between neutrino and antineutrino oscillations at the H" eV2 scale. The MiniBooNE experiment observes an unexplained excess of electron-like events at low energies in neutrino mode, which may be due, for example, to either a neutral current radiative interaction, sterile neutrino decay, or to neutrino oscillations involving sterile neutrinos and which may be related to the LSND signal. No excess of electron-like events ( -0.5 ± 7.8 ± 8.7), however, is observed so far at low energies in antineutrino mode. Furthermore, global 3+1 and 3+2 sterile neutrino fits to the world neutrino and antineutrino data suggest a difference between neutrinos and antineutrinos with significant (sin2 2[theta]{sub [mu]{mu}} H"35%) {bar [nu]}{sub {mu}} disappearance. In order to test whether the low-energy excess is due to neutrino oscillations and whether there is a difference between [nu]{sub {mu}} and {bar [nu]}{sub {mu}} disappearance, we propose building a second MiniBooNE detector at (or moving the existing MiniBooNE detector to) a distance of H"00 m from the Booster Neutrino Beam (BNB) production target. With identical detectors at different distances, most of the systematic errors will cancel when taking a ratio of events in the two detectors, as the neutrino flux varies as 1/r2 to a calculable approximation. This will allow sensitive tests of oscillations for both {nu}{sub e} and {bar {nu}} appearance and {nu}{sub {mu}} and {bar {nu}}{sub {mu}} disappearance. Furthermore, a comparison between oscillations in neutrino mode and antineutrino mode will allow a sensitive search for CP and CPT violation in the lepton sector at short baseline ([Delta]m2> 0.1 eV2). Finally, by comparing the rates for a neutral current (NC) reaction, such as NC [pi]° scattering or NC elastic scattering, a direct search for sterile neutrinos will be made. The initial amount of running time requested for the near detector will be a total of H"E20 POT divided between neutrino mode and antineutrino mode, which will provide statistics comparable to what has already been collected in the far detector. A thorough understanding of this short-baseline physics will be of great importance to future long-baseline oscillation experiments.
NOvA is a long-baseline neutrino oscillation experiment that uses two functionally identical detectors separated by 810 kilometers at locations 14 milliradians o -axis from the NuMI muon neutrino beam at Fermilab. At these locations the beam energy peaks at 2 GeV. This baseline is the longest in the world for an accelerator-based neutrino oscillation experiment, which enhances the sensitivity to the neutrino mass ordering. The experiment studies oscillations of the muon neutrino and anti-neutrino beam that is produced. Both detectors completed commissioning in the summer of 2014 and continue to collect data. One of the primary physics goals of the experiment is the measurement of electron neutrino appearance in the muon neutrino beam which yields measurements of the oscillation parameters sin22[theta]13, [delta], and the neutrino mass ordering within the standard model of neutrino oscillations. This thesis presents the analysis of data collected between February 2014 and May 2015, corresponding to 3.52 X 1020 protons-on-target. In this first analysis NOvA recorded 6 electron neutrino candidates which is a 3.3[sigma] observation of electron neutrino appearance. The T2K experiment performs the same measurement on a baseline of 295 kilometers and has a 1 [sigma] preference for the normal mass ordering over the inverted ordering over the phase space of the CP violating parameter [delta], which is also weakly seen in the NOvA result. By the summer of 2016 NOvA will triple its statistics due to increased beam power and a completed detector. If electron neutrinos continue to be observed at the current rate NOvA will be able to establish a mass ordering preference at a similar con dence level to T2K.
A sensitive search for inclusive neutrino oscillations has been performed using two similar detectors running simultaneously at different locations in the Fermilab dichromatic muon-neutrino beam. The preliminary results show no significant oscillation signal and rule out inclusive oscillations of muon neutrinos into any other type of neutrons for 20 .delta.m2
The MiniBooNE Collaboration reports a search for [nu]{sub {mu}} and {bar [nu]}{sub {mu}} disappearance in the [Delta]m2 region of a few eV2. These measurements are important for constraining models with extra types of neutrinos, extra dimensions and CPT violation. Fits to the shape of the {nu}{sub {mu}} and {bar {nu}}{sub {mu}} energy spectra reveal no evidence for disappearance at 90% confidence level (CL) in either mode. This is the first test of {bar {nu}}{sub {mu}} disappearance between [Delta]m2 = 0.1-10 eV2.