V. Eberhard

The high resolution neutrino calorimeter KARMEN

Abstract KARMEN is a 56 t scintillation calorimeter designed for beam dump neutrino experiments at the neutron spallation facility ISIS of the Rutherford Appleton Laboratory. The calorimetric properties are demonstrated by cosmic muons and laser calibration. The measured energy resolution of the detector is σ E / E ≈ 11.5%/√ E [MeV], the position resolution σ x = 5 cm and the timing resolution σ t ≈ 350 ps.

Anomaly in the time distribution of neutrinos from a pulsed beam stop source

Abstract Analysis of the charged and neutral current reactions 12 C (ν e , e − ) 12 N and 12 C (ν, ν′) 12 C ∗ 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.

First observation of the neutral current nuclear excitation 12C(v,v′)12C∗(1+, 1)

Abstract The neutral current nuclear excitation 12 (v,v′) 12 C ∗ (1 + , 1; 15.1 MeV) has been observed for the first time. For v e and v μ from μ + -decay at rest the flux averaged cross section was determined to be NC (v e + v μ ) > = [10.8±5.1 (stat.) ±1.1 (syst.)]×10 −42 cm 2 .

Cross section of the charged current reaction 12C(ve, e−)12Ng.s.

Abstract The charged current nuclear transition 12 C(v e , e − ) 12 N g.s. has been observed in the KARMEN experiment. The flux average cross section for ve from μ+ decay at rest is determined to be 〈σ〉 = [8.1±0.9(stat.)±0.75 (syst.)]×10−42cm2. For the first time also the energy dependence of the cross section has been measured for neutrino energies up to 50 MeV.

Cross-section of the charged current reaction C-12 (electron-neutrino e-) N-12 (g.s.).

Abstract The charged current nuclear transition 12 C(v e , e − ) 12 N g.s. has been observed in the KARMEN experiment. The flux average cross section for ve from μ+ decay at rest is determined to be 〈σ〉 = [8.1±0.9(stat.)±0.75 (syst.)]×10−42cm2. For the first time also the energy dependence of the cross section has been measured for neutrino energies up to 50 MeV.

Measurement of the weak neutral current excitation 12C(νμνμ′)12C∗(1+,1;15.1MeV) at Eνμ=29.8 MeV

Abstract The weak neutral current reaction 12 C( ν μ , ν μ ′ ) 12 C ∗ (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 σ NC =(3.2 ± 0.5 stat. ± 0.4 syst. ) × 10 −42 cm 2 for monoenergetic ν μ 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.

Neutrino oscillation results from KARMEN

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides νμs, νes and νμs 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.

Spectral attenuation length of scintillating fibers

Abstract A double spectrometer allows the precise measurement of the spectral attenuation length of scintillating fibers. Exciting the fibers with a N 2 -laser at different points and measuring the wavelength dependent light intensity on both ends of the fiber simultaneously, enables a measurement of the attenuation length which is practically independent of systematic uncertainties. The experimental setup can additionally be used for the measurement of the relative light output. Six types of scintillating fibers from four manufactures (Bicron, Kuraray, Pol.Hi.Tech, and Plastifo) were tested. For different fibers the wavelength dependent attenuation lengths were measured from 0.3 m up to 20 m with an accuracy as good as 1%.

Limits on neutrino oscillations in the appearance channels vμ → ve and vμ → ve

The KARMEN experiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos v μ , v e and v μ from π + and μ + decay at rest to search for neutrino oscillations in the appearance modes v μ → v e and v μ → v 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 v e and v 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 Θ ≥ 0.0062 in the v μ → v e channel and sin 2 2 Θ ≥ 0.048 in the v μ → v e channel for the region Δm 2 > 1 eV 2

KARMEN at ISIS: The advantage of a pulsed neutrino source in the search for neutrino oscillations and neutrino nuclear interactions

Abstract KARMEN, the Karlsruhe-Rutherford Medium Energy Neutrinoexperiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos νμ, νe and ν μ from π+ and μ+ decay at rest to search for neutrino oscillations in the appearance channels νμ → νe and ν μ → ν e. 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.