Search for heavy neutrinos mixing with tau neutrinos

We report on a search for heavy neutrinos (\nus) produced in the decay D_s\to \tau \nus at the SPS proton target followed by the decay \nudecay in the NOMAD detector. Both decays are expected to occur if \nus is a component of $\nu_{\tau}$.\ From the analysis of the data collected during the 1996-1998 runs with $4.1\times10^{19}$ protons on target, a single candidate event consistent with background expectations was found. This allows to derive an upper limit on the mixing strength between the heavy neutrino and the tau neutrino in the \nus mass range from 10 to 190 $\rm MeV$. Windows between the SN1987a and Big Bang Nucleosynthesis lower limits and our result are still open for future experimental searches. The results obtained are used to constrain an interpretation of the time anomaly observed in the KARMEN1 detector.\Comment: 20 pages, 7 figures, a few comments adde

The CERN Axion Solar Telescope (CAST)

A decommissioned LHC test magnets is being prepared as the CERN Axion Solar Telescope (CAST) experiment. The magnet has a field of 9.6 Tesla and length of 10 meters. It is being mounted on a platform to track the sun over +/-8(0) vertically and +/-45(0), horizontally. A sensitivity in axion-photon coupling g(agammagamma) < 5 x 10(-11)GeV(-1) can be reached for m(a) less than or equal to 10(-2) eV, and with a gas filled tube-can reach g(agammagamma) less than or equal to 10(-10)GeV(-1) for axion masses m(a) < 2eV

Search for eV (pseudo)scalar penetrating particles in the SPS neutrino beam

We carried out a model-independent search for light scalar or pseudoscalar particles a's (an example of which is the axion) that couple to two photons by using a photon-regeneration method at high energies allowing a substantial increase in the sensitivity to eV masses. The experimental set-up is based on elements of the CERN West Area Neutrino Facility (WANF) beam line and the NOMAD neutrino detector. The new particles, if they exist, could be produced through the Primakoff effect in interactions of high energy photons, generated by the 450 GeV protons in the CERN SPS neutrino target, with virtual photons from the WANF horn magnetic field. The particles would penetrate the downstream shielding and would be observed in the NOMAD neutrino detector through their re-conversion into real high energy photons by interacting with the virtual photons from the magnetic field of the NOMAD dipole magnet. From the analysis of the data collected during the 1996 run with 1.08*10/sup 19/ protons on target, 312 candidate events with energy between 5 and 140 GeV were found. This number is in general agreement with the expectation of 272+or-18 background events from standard neutrino processes. A 90% CL upper limit on the a gamma gamma -coupling g/sub a gamma gamma / lt 1.5*10/sup -4/ GeV/sup -1/ for a masses up to 40 eV is obtained

New results on a search for a 33.9 MeV/c² neutral particle from π⁺ decay in the NOMAD experiment

We report on a direct search in NOMAD for a new 33.9 MeV/c(2) neutral particle (X) produced in pion decay in flight, pi --> muX followed by the decay X --> nue(+)e(-). Both decays are postulated to occur to explain the time anomaly observed by the KARMEN experiment. From the analysis of the data collected during the 1996-1998 runs with 4.1 x 10(19) protons on target, a single candidate event consistent with background expectations was found. The search is sensitive to a pion branching ratio BR(pi --> muX) > 3.7 x 10(-15), significantly smaller than previous experimental limits