Ion Stancu

THE LIQUID SCINTILLATOR NEUTRINO DETECTOR AND LAMPF NEUTRINO SOURCE

Abstract A search for neutrino oscillations of the type ν μ → ν c has been conducted at the Los Alamos Meson Physics Facility using ν μ from muon decay at rest. Evidence for this transition has been reported previously. This paper discusses in detail the experimental setup, detector operation and neutrino source, including aspects relevant to oscillation searches in the muon decay-at-rest and pion decay in flight channels.

Hierarchical four-neutrino oscillations with a decay option

We present a new and novel synthesis of all existing neutrino data regarding the disappearance and appearance of {nu}{sub e} and {nu}{sub {mu}}. We assume four neutrinos: {nu}{sub e},{nu}{sub {mu}},{nu}{sub {tau}}, as well as a heavier singlet neutrino {nu}{sub s} of a few eV. The latter may decay into a massless Goldstone boson (the singlet Majoron) and a linear combination of the doublet antineutrinos. We comment on how this scenario may be verified or falsified in future experiments. We point out how it allows us to evade the CDHSW constraints. (c) 2000 The American Physical Society.

Neutrino oscillations with LSND

The Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos Meson Physics Facility (LAMPF) has conducted searches for νν → νe oscillations using νμ from μ+ decay at rest (DAR) and for νμ → νe oscillations using νμ from π+ decay in flight (DIF). For the 1993–1995 data taking period, significant beam-excess events have been found in both oscillation channels. For the DAR search, a total excess of 51.8−16.9+18.7 ± 8.0 events from the νe p → e+n inverse β-decay reaction is observed, with e+ energies between 20–60 MeV. For the DIF search, a total excess of 18.1 ± 6.6 ± 4.0 events from the νe C → e− X inclusive reaction is observed, with e− energies between 60–200 MeV. If interpreted as neutrino oscillations, these excesses correspond to oscillation probabilities of (3.1 ± 1.2 ± 0.5) × 10−3 and (2.6 ± 1.0 ± 0.5) × 10−3, respectively. Additional data collected during the 1996–1998 runs has been preliminarily analyzed for the DAR channel and yields very good agreement with the previously obtained results, for a combined oscillation probability of (3.3 ± 0.9 ± 0.5) × 10−3.

The future of the short-baseline neutrino oscillation experiments in the US: MiniBooNE and ORLaND

Following the potential oscillation signals from LSND, several short-baseline neutrino oscillation experiments are currently in different development stages in the US. They are targeted at unambiguously confirming or dismissing these observations. The MiniBooNE experiment at FermiLab will focus on the vμ → ve appearance channel using a decay-in-flight vμ beam. The ORLaND experiment at the Oak Ridge National Laboratory will focus on the vμ → ve decay-at-rest channel, while being able to perform a wide variety of neutrino physics in parallel to the oscillation searches.

Measurement of the proton’s axial form factor via neutrino‐nucleon scattering

Recent experimental and theoretical work indicates that strange quark pairs play a non‐negligible role in determining nucleon properties. Their effects contribute to the electroweak nucleon form factors and thus can be isolated through measurements of neutral weak neutrino‐nucleon scattering. In particular, the ss contribution to the nucleon spin can be determined by measuring the ratio of proton‐to‐neutron neutrino‐induced quasielastic yield. Preliminary results from the LSND experiment are presented, experiment which, at the end of the scheduled 94–95 run period, should obtain a measurement of the strange axial form factor, Gs1(0), with an absolute accuracy of approximately ±0.04.

Further evidence for neutrino oscillations from LSND: the νμ → νe decay-in-flight channel

A search for νμ → νe oscillations has been conducted at the Los Alamos Meson Physics Facility (LAMPF) using νμ from π+ decay in flight. An excess in the number of beam-related events from the νe C → e− X inclusive reaction is observed. The excess is too large to be explained by normal νe contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 ± 1.3 ± 0.5) × 10−3 is consistent with the previously reported νμ → νe oscillation evidence from LSND.

CAN THE SUPER-KAMIOKANDE ATMOSPHERIC DATA PREDICT THE SOLAR NEUTRINO DEFICIT?

In this letter we show that the evidence for neutrino oscillations from the super-Kamiokande atmospheric neutrino data fully determines the 3×3 neutrino-oscillations mixing matrix and predicts an energy-independent solar neutrino deficit at the level of 45%. This corresponds to a ratio of measured to predicted neutrino flux of , in good agreement with the experimental results. We achieve this result within the framework of a minimal, three-generation neutrino mixing, with mass squared differences of ΔM2≃0.45 eV2 and . The mixing matrix derived here is characterized by the mixing angles θ=35.1°, β=5.5° and ψ=23.3°, and a vanishing CP-violating phase, δ=0.