E. Knoops

First observation of neutrino trident production

Abstract We report on the first observation of neutrino induced production of muon pairs in the electromagnetic field of a nucleus. The data has been obtained using the CHARM II detector exposed to the CERN wideband neutrino and antineutrino beams. A clear signal of 55 ± 16 events is seen in a sample of dimuons of opposite charge without visible recoil at the vertex. The cross section is determined and found to be in agreement with the standard model prediction.

Search for νμ → ντ oscillation

Abstract The fine granularity of the CHARM-II detector has been exploited to search, in the CERN-SPS wide band neutrino beam, for quasi-elastic ντ interactions followed by the decay τ → πντ. Since the sampling thickness of the target calorimeter corresponds to ∼ 1 9 of an interaction length, these events appear in the detector as a single track followed by a hadronic shower. The study of the “single pion” events is used to set limits on the νμ → ντ oscillation parameters. The maximum sensitivity to the mixing angle θ is reached for Δm2 = 50 eV2 allowing to exclude values of sin22θ greater than 6.4 × 10−3 at 90% CL.

Neutral current coupling constants from neutrino- and antineutrino-electron scattering

Abstract We are reporting on a determination of neutral current coupling constants from a study of differential cross sections of muon- (anti)neutrino-electron scattering. The results were obtained with the CHARM-II detector which was exposed to the CERN wide band neutrino beam in the years 1987–1990. A total of about 2100 ve and 2200 ve scattering events were observed. From a comparison between the data and predicted event distributions, the effective vector and axial-vector neutral current coupling constants of the electron were determined to be g e v =−0.025±0.019 and g e A =−0.503±0.018.

A new determination of the electroweak mixing angle from muon-neutrino electron scattering

Abstract We are reporting on a new determination of sin2ϑw from the ratio of v μ e to v e scattering cross sections. A new detector designed for this purpose was exposed tothe Wide Band Neutrino Beamof the 450 GeV (CERN SPS. An analysis of data taken in 1987 and 1988 is presented based on 762 vμe and 1017 v e events. From the ratio of σ( v μ e ) to σ( v μ e ) we determined sin2ϑw=0.233±0.012 (stat) ± 0.008 (syst) without radiative correction. With radiative correction for mt=mH=100 GeV we find sin2ϑw=0.232±0.012(stat)±0.008(syst).

An Improved determination of the electroweak mixing angle from muon-neutrino electron scattering

Abstract We are reporting an improved determination of the electroweak mixing angle sin2Θw from the ratio of νμe to ν μ e scattering cross sections. The CHARM II detector was exposed to neutrino and antineutrino wide band beams at the 450 GeV CERN SPS. Including new data collected in 1989 we have obtained 1316 ± 56 νμe and 1453 ± 62 ν μ e events. From the ratio of the visible cross sections we determined sin2Θ0=0.239 ± 0.009(stat) ± 0.007(syst) without radiative corrections and g V e g A e =0.047 ± 0.046 . Combining this last result with recent results on gAe at LEP we obtain gVe= −0.023 ± 0.023.

Coherent single charged pion production by neutrinos

Abstract We report on a measurement of coherent single charged pion production in neutrino-nucleus scattering. The analysis is based on data taken with the CHARM II detector in beams of muon-neutrinos and -antineutrinos. The event numbers amount to N ( μ − π ) = 748 and N ( μ + π ) = 631. Cross sections and their dependence on the neutrino energy are determined. The results are in agreement with the predictions of models based on the PCAC hypothesis.

Experimental study of electromagnetic properties of the muon-neutrino in neutrino - electron scattering

Abstract We report new bounds on electromagnetic properties of the muon neutrino obtained from a study of neutrino-electron scattering. The results are based on the analysis of differential cross section data collected with the CHARM II detector. The 90% C.L. limit on the magnetic moment of the muon-neutrino μ ν μ −9 μ B confirms limits obtained at much lower energies. The limit on the anomalous charge radius of the muon neutrino |〈 r 2 〉 anom | −33 cm 2 im earlier results by nearly a factor three.

A Precise measurement of the cross-section of the inverse muon decay muon-neutrino + e- --> mu- + electron-neutrino

We report our final results from the analysis of the full high statistics sample of events of the reaction up + e- --+ /*- + v, collected with the CHARM II detector in the CERN wide-band neutrino beam during the years 1988 to 1991. From a signal of 15 758 f 324 inverse muon decay events we derived, in the Born approximation, a value of ( 16.51 f 0.93) x lO-42 cm*GeV-’ for the asymptotic cross section slope a/E,, in good agreement with the Standard Model prediction of 17.23 x IO-” cm* GeV- ‘. The result constrains the scalar coupling of the electron and the muon to [&l’ < 0.475 at 90% CL.

Flavour universality of neutrino couplings with the Z

Abstract We are reporting the first experimental result of the coupling of the muon neutrino with the Z. This result is in good agreement with the average value of the coupling of the three neutrino families as derived from the invisible decay width of the Z. We also determined g ν τ assuming N ν =3.

Search for muon to electron neutrino oscillations

AbstractA search for νμ → νe and