Accelerator-based neutrino experiment is reviewed. Among various activities on this research field, the most fascinating subject is to search for neutrino oscillations and the confirmation of this phenomenon. In this article, mainly neutrino oscillation experiment, with especially focusing on the presently active experiment, K2K, is discussed. The future prospect on the confirmation of neutrino oscillation is also described.

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides νμ's, νe's and νμ's in equal intensities from the π+-μ+-decay at rest (DAR). The oscillation channels νμ → νe and νμ → νe are investigated in the appearance mode with a 56t liquid scintillation calorimeter at a mean distance of 17.7m from the ν-source. Analyses of experimental data from the measuring period 1990–1995 corresponding to 9122 C protons on target or 2.52 · 1021μ+ DAR are presented. No evidence for oscillations could be found with KARMEN, resulting in 90% CL exclusion limits of sin2(2θ) < 8.5·10−3 (νμ → νe) and sin2(2θ) < 4.0·10−2 (νμ → νe) for Δm2 ≥ 100 eV2 in a simple 2 flavor description of ν-oscillations.

KARMEN, the Karlsruhe-Rutherford Medium Energy Neutrinoexperiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos νμ, νe and νμ from π+ and μ+ decay at rest to search for neutrino oscillations in the appearance channels νμ → νe and νμ → νe. The signature for both oscillations is based on charged current neutrino nuclear interaction spectroscopy in a high resolution 56 t liquid scintillator calorimeter. The detector system has been upgraded with an additional veto layer during 1996 to eliminate cosmogenic background and to enhance its sensitivity in the oscillation channels. This report describes the results based on data acquired from June 1990 to August 1995 and the first data of 1997 with the new veto system in operation.

The 56 ton high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{x}.$ The ${\ensuremath{\nu}}_{e}$ emitted in ${\ensuremath{\mu}}^{+}$ decay at rest are detected with spectroscopic quality via the exclusive charged current reaction ${}^{12}\mathrm{C}({\ensuremath{\nu}}_{e}{,e}^{\ensuremath{-}}{)}^{12}{\mathrm{N}}_{\mathrm{g}.\mathrm{s}.}$ almost free of background. Analysis of the spectral shape of ${e}^{\ensuremath{-}}$ from the ${\ensuremath{\nu}}_{e}$-induced reaction as well as a measurement of the absolute ${\ensuremath{\nu}}_{e}$ flux allows one to investigate oscillations of the type ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}.$ The flux-independent ratio ${R}_{\mathrm{C}\mathrm{C}/\mathrm{N}\mathrm{C}}$ of charged current events ${}^{12}\mathrm{C}({\ensuremath{\nu}}_{e}{,e}^{\ensuremath{-}}{)}^{12}{\mathrm{N}}_{\mathrm{g}.\mathrm{s}.}$ to neutral current events ${}^{12}{\mathrm{C}(\mathrm{\ensuremath{\nu}},\mathrm{\ensuremath{\nu}}}^{\ensuremath{'}}{)}^{12}{\mathrm{C}}^{*}$ provides additional information in the oscillation channel ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{x}.$ All three analysis methods show no evidence for oscillations. For the ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ channel 90% confidence limits of ${\mathrm{sin}}^{2}(2\ensuremath{\Theta})<0.338$ for $\ensuremath{\Delta}{m}^{2}>~100{\mathrm{eV}}^{2}{/c}^{4}$ and $\ensuremath{\Delta}{m}^{2}<0.77{\mathrm{eV}}^{2}{/c}^{4}$ for maximal mixing in a simple two-flavor oscillation formalism are derived. A complete three-flavor analysis of the experimental data from 5 years of measurement with respect to ${\ensuremath{\nu}}_{e}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\ensuremath{\nu}}_{e}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}$ mixing is presented.

The weak neutral current reaction 12C(νμ,νμ′)12C∗ (1+,1; 15.1MeV) has been observed for the first time in the KARMEN experiment. Neutrino events were separated from background using two different analysis methods. The measured cross section σNC=(3.2 ± 0.5stat. ± 0.4syst.) × 10−42 cm2 for monoenergetic νμ from π+-decay at rest is in good agreement with the standard model, the isovector-axialvector coupling constant of weak hadronic current deduced from this experiment is |β|=1.11±0.13.

The 56 ton high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel nu(e)-nu(x). The nu(e) emitted in mu(+) decay at rest are detected with spectroscopic quality via the exclusive charged current reaction C-12(nu(e),e(-))N-12(g.s.) almost free of background. Analysis of the spectral shape of e(-) from the nu(e)-induced reaction as well as a measurement of the absolute nu(e) flux allows one to investigate oscillations of the type nu(e) --> nu(tau) and nu(e) --> nu(mu). The flux-independent ratio R-CC/NC of charged current events C-12(nu(e) , e(-))N-12(g.s.) to neutral current,events C-12(nu,nu')C-12* provides additional information in the oscillation channel nu(e) --> v(tau). All three analysis methods show no evidence for oscillations. For the nu(e) --> nu(tau) channel 90% confidence limits of sin(2)(2 Theta)<0.338 for Delta m(2) greater than or equal to 100 eV(2)/c(4) and Delta m(2)<0.77 eV(2)/c(4) for maximal mixing in a simple two-flavor oscillation formalism are derived. A complete three-flavor analysis of the experimental data from 5 years of measurement with respect to nu(e) <-> nu(tau) nu <-> nu(mu) mixing is presented.

The KARMEN experiment uses the reaction C-12(v(e), e(-))N-12(g.s.) to measure the energy distribution of v(e) emitted in muon decay at rest mu(+) --> e(+) + v(e) + (v) over bar(mu). The v(e) analog omega(L) of the famous Michel parameter rho has been derived from a maximum-likelihood analysis of events near the kinematic end point, E-max = 52.8 MeV. The result, omega(L) = (2.7(-3.3)(+3.8) +/- 3.1) x 10(-2), is in good agreement with the standard model prediction omega(L) = 0. We deduce a 90% confidence upper limit of omega(L) less than or equal to 0.113, which corresponds to a limit of \g(RL)(S) + 2g(RL)(T)\ less than or equal to 0.78 on the interference term between scalar and tensor coupling constants.

For low energy tests of the standard model by v-e scattering and the determination of v-16O cross sections a high resolution 1.3 kt H2O Cherenkov detector is under evaluation. The results of extensive Monte Carlo simulations are presented. The goal is a high resolution Cherenkov detector with time resolution of 0.6 ns and energy resolution of 17% at Ee = 15 MeV.

The KARMEN experiment at the pulsed neutron facility ISIS is investigating neutrino-nucleus reactions and neutrino oscillations. In this paper we present cross sections for neutrino induced charged and neutral current reactions on C-12. These results allow a precision test of the standard model of weak interaction by imposing new limits on the neutral current isovector axial vector coupling strength beta(A), the strength parameter rho measuring the universality of W+/- and Z(0) coupling in the low energy regime and by investigating the Lorentz, structure of muon decay. Neutrino oscillations (v) over bar (mu)-->(v) over bar (e) are investigated in the appearance mode by looking for p((v) over bar (e), e(+))n reactions. An analysis of 3 years running time with the KARMEN2 setup reveals no indication of an oscillation signal excluding most parts of the LSND oscillation evidence.

Analysis of the charged and neutral current reactions 12C(νe, e−) 12N and 12C(ν, ν′) 12C∗ induced by neutrinos from π+- and μ+-decays at rest reveals an anomaly in the time distribution after all π+ have decayed: the measured time constant for subsequent events differs substantially from the value of 2.2 μs corresponding to the μ+ lifetime. This anomaly cannot currently be explained by background processes or errors in the experimental set-up. A satisfactory description of the time spectrum is achieved by assuming it has two components, one exponential with a 2.2 μs time constant, the other a Gaussian signal of 83±28 events at 3.6 μs after beam-on-target. A speculative explanation, but one fully consistent with all the data, is that these delayed events originate from the decay of a slowly moving (β∼0.02) massive neutral particle produced in the beam stop. Further measurements to improve statistical significance are necessary.

The KARMEN experiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos vμ, ve and v̄μ from π+ and μ+ decay at rest to search for neutrino oscillations in the appearance modes vμ → ve and v̄μ → v̄e. A high resolution 56 ton liquid scintillation calorimeter located at a mean distance of 17.5 m from the proton beam stop allows identification of ve and v̄e with spectroscopic quality. We report the status of our search for neutrino oscillations after four years of running. No positive evidence for neutrino oscillations has been observed in both appearance channels. The 90 % CL limits of this experiment exclude mixing angles sin2 2 Θ ≥ 0.0062 in the v̄μ → v̄e channel and sin2 2 Θ ≥ 0.048 in the vμ → ve channel for the region Δm2 > 1 eV2

The KARMEN experiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos nu(mu), nu(e) and <(nu)over bar>(mu) from pi(+) and mu(+) decay at rest to search for neutrino oscillations in the appearance modes nu(mu) --> nu(e) and <(nu)over bar>(mu) --> <(nu)over bar>(e). A high resolution 56 ton liquid scintillation calorimeter located at a mean distance of 17.5 m from the proton beam stop allows identification of nu(e) and <(nu)over bar>(e) with spectroscopic quality. We report the status of our search for neutrino oscillations after four years of running. No positive evidence for neutrino oscillations has been observed in both appearance channels. The 90 % CL Limits of this experiment exclude mixing angles sin(2)2 Theta greater than or equal to 0.0062 in the <(nu)over bar>(mu) --> <(nu)over bar>(e) channel and sin(2)2 Theta greater than or equal to 0.048 in the nu(mu) --> nu(e) channel for the region Delta m(2) > 1 eV(2)

The KARMEN experiment at the pulsed spallation neutron facility ISIS studies the charged and neutral current reactions C-12 (nu(e),e(-)) N-12 and C-12 (nu,nu') C-12* (1(+)1) in the astrophysical important energy range up to 50 MeV. Neutrinos are detected by a 56 ton high resolution Liquid scintillation calorimeter with spectroscopic quality. Efficient background rejection results in clear neutrino signatures and allows reliable cross section measurements down to 10(-42) cm(2) We present cross section results for nu-induced reactions on carbon with special emphasis on their implications for neutrino astrophysics and weak nuclear formfactors and report a new flux-independent test of the equality of the couplings of nu(e) and <(nu)over bar>(mu) to the weak neutral current at low energies.