E. Finckh

Upper limits for neutrino oscillations ν ¯ μ → ν ¯ e from muon decay at rest

The KARMEN experiment at the spallation neutron source ISIS used \numub from \mup--decay at rest in the search for neutrino oscillations \numubnueb in the appearance mode, with p(\nueb,e+)n as detection reaction of \nueb. In total, 15 candidates fulfill all conditions for the \nueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta) 100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for \numubnueb.

Differential cross section of the 2H(n, nnp)-reaction at En = 13MeV

Abstract The differential cross section of the nD break-up reaction was investigated at En = 13 MeV using the Erlangen multidetector neutron facility. Twenty-two different configurations including np final-state interaction, collinearity, coplanar- and space star were measured in a kinematically complete experiment. The results are compared with rigorous Faddeev calculations based on the Paris potential. The discrepancies between data and calculations indicate imperfections in the potential and may be caused by three-particle effects such as wrong off-shell behavior of the potential or an additional three-body force.

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.

Upper limits for neutrino oscillations muon-anti-neutrino ---> electron-anti-neutrino from muon decay at rest

The KARMEN experiment at the spallation neutron source ISIS used \numub from \mup--decay at rest in the search for neutrino oscillations \numubnueb in the appearance mode, with p(\nueb,e+)n as detection reaction of \nueb. In total, 15 candidates fulfill all conditions for the \nueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta) 100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for \numubnueb.

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 .

The neutron detection efficiency of NE213 detectors measured by means of a 252Cf source

Abstract The neutron detection efficiency of a NE213 scintillator was determined by comparing the measured neutron time-of-flight spectrum of a 252 Cf source with its reference neutron energy distribution. Below E n = 8 MeV an accuracy of better than 3% could be achieved. The measured efficiency agreed reasonably well in shape with a Monte Carlo simulation in the entire energy range 0.8 MeV ⩽ E n ⩽ 13 MeV, but the calculation is generally about 5% lower than the experimental values.

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.

The Erlangen AMS facility: status report and research program☆

Abstract We report on technical developments at the Erlangen AMS facility since 1993. These include modifications to the ionizer and sample changer, improvements in the vacuum system throughout the machine and the installation of new accelerator tubes. For sample preparation the full line from AAA pretreatment, oxidation to carbon dioxide and catalytic reduction to carbon has been established. For very small samples of less than 500 μg carbon a new reduction facility with a total volume of 3.8 cm 3 has been built and is being optimized. We also give a short outline of the research programs currently being carried out and those planned for the near future.

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.