N.E. Booth

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.

Neutrino interactions with carbon: recent measurements and a new test of νe, νμ universality

Abstract The charged and neutral current reactions 12 C (ν e , e − ) 12 N g.s. and 12 C (ν, ν) 12 C ∗ [1 + , 1; 15.1 MeV have been studied with cumulative neutrino fluxes an order of magnitude greater than reported previously. Flux-averaged cross sections of [9.1±0.5 stat ±0.8 syst ]×10 −42 cm 2 and [10.4±1.0 stat ±0.9 syst ]×10 −42 cm 2 respectively are in excellent agreement with theoretical calculations. The energy dependence of the charged current reaction has also been measured. The ratio of cross sections provides a flux-independent test of equality of the couplings of ν e and ν μ to the weak neutral current for |q 2 | −3 ( GeV c ) 2 , and is in good agreement with the universality postulate.

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.

New experimental limits on νe→ντ oscillations in 2-ν and 3-ν mixing schemes

The 56 tonne 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->x. The nu_e emitted in mu+ decay at rest are detected with spectroscopic quality via the exclusive charged current reaction 12-C(nu_e,e-)12-N_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 allow 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 12-C(nu_e,e-)12-N_g.s. to neutral current events 12-C(nu,nu)12-C* provides additional information in the oscillation channel nu_e->x . All three analysis methods show no evidence for oscillations. For the nu_e->nu_tau channel 90%CL limits of sin^2(2t) 100eV^2 and dm^2 nu_tau and nu_e nu_mu mixing is presented.

KARMEN limits on electron-neutrino ---> tau-neutrino oscillations in two neutrino and three neutrino mixing schemes

The 56 tonne 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->x. The nu_e emitted in mu+ decay at rest are detected with spectroscopic quality via the exclusive charged current reaction 12-C(nu_e,e-)12-N_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 allow 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 12-C(nu_e,e-)12-N_g.s. to neutral current events 12-C(nu,nu)12-C* provides additional information in the oscillation channel nu_e->x . All three analysis methods show no evidence for oscillations. For the nu_e->nu_tau channel 90%CL limits of sin^2(2t) 100eV^2 and dm^2 nu_tau and nu_e nu_mu mixing is presented.

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.

Determination of the nuclear weak axial charge radius of 12C via the 12C(νe, e−) 12Ng.s. reaction

Abstract A recent measurement of the charged current reaction 12 C (ν e , e − ) 12 N g.s. has been used to investigate the weak axial vector form factor FA(q2) for 12 C in the range |q2| ≤ 0.4 m2π. The analysis yields a rms radius of the weak axial charge RA=(3.7+1.3−1.8) fm corresponding in a dipole form to a mass parameter MA=(180+200−45) MeV/c2 in agreement with results deduced from inelastic electron scattering. From the total number of observed events the value at q2=0, FA(0)=0.73+0.11−0.10, was derived.

Results from the KARMEN neutrino experiment

Abstract KARMEN denotes an experimental program of neutrino physics using a pulsed source of neutrinos ν μ , ν e and ν μ with energies up to 52.8 MeV and a 56 t scintillation calorimeter. Major physics aims are the measurement of charged current (CC) as well as neutral current (NC) neutrino nuclear interactions on 12 C with their implications for specific weak couplings, nuclear formfactors and μ-e universality and the search for neutrino oscillations ν μ →ν e and ν μ → ν e . We present the results of the KARMEN experiment from its first two years of data taking.