The Search for Neutrino Oscillations numubar->nuebar with KARMEN

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides numu's, nue's and numubar's in equal intensities from the pi+ mu+ decay at rest (DAR). The oscillation channel numub->nueb is investigated in the appearance mode with a 56t liquid scintillation calorimeter at a mean distance of 17.7m from the nu source looking for p(nue,e+)n reactions. The cosmic induced background for this oscillation search could be reduced by a factor of 40 due to an additional veto counter installed in 1996. In the data collected through 1997 and 1998 no potential oscillation event was observed. Using a unified approach to small signals this leads to an upper limit for the mixing angle of sin**2(2t) < 1.3x10^{-3} (90%CL) at large Dm**2. The excluded area in (sin**2(2t),Dm**2) covers almost entirely the favored region defined by the LSND numub->nueb evidence.Comment: Proceedings Contribution to Neutrino98 in Takayama, Japan, June 4-9, 1998; 13 pages, including 4 figure

Off-diagonal structure of neutrino mass matrix in see-saw mechanism and electron-muon-tau lepton universality

By a simple extension of the standard model in which ($e-\mu -\tau$) universality is not conserved, we present a scenario within the framework of see-saw mechanism in which the neutrino mass matrix is strictly off-diagonal in the flavor basis. We show that a version of this scenario can accomodate the atmospheric $\nu_\mu -\nu_\tau$ neutrino oscillations and $\nu_\mu -\nu_e$ oscillations claimed by the LSND collaboration. PACS: 14.60.Pq; 14.60.St;13.15.+gComment: 5 pages, Revtex, 1 figure: The model accomodate another version which explains atmospheric neutrino data and the observed solar neutrino oscillations (large angle solution). In the previous version the value of \lambda parameter is changed to the expected one. This version now accomodates LSND result and solar neutrino oscillations (small angle MSW solution

Improved limits on nuebar emission from mu+ decay

We investigated mu+ decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for \nueb via the detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays was identified. We extract upper limits of the branching ratio for the LF violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ -> e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which \nueb emission from mu+ decay is allowed with considerable strength. The decay \mupdeb as source for the \nueb signal observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl

Detector Control System of the ATLAS Insertable B-Layer

soumis à publicationTo improve tracking robustness and precision of the ATLAS inner tracker an additional fourth pixel layer is foreseen, called Insertable B-Layer (IBL). It will be installed between the innermost present Pixel layer and a new smaller beam pipe and is presently under construction. As, once installed into the experiment, no access is available, a highly reliable control system is required. It has to supply the detector with all entities required for operation and protect it at all times. Design constraints are the high power density inside the detector volume, the sensitivity of the sensors against heatups, and the protection of the front end electronics against transients. We present the architecture of the control system with an emphasis on the CO2 cooling system, the power supply system and protection strategies. As we aim for a common operation of pixel and IBL detector, the integration of the IBL control system into the Pixel one will be discussed as well

A Compact Beam Stop for a Rare Kaon Decay Experiment

We describe the development and testing of a novel beam stop for use in a rare kaon decay experiment at the Brookhaven AGS. The beam stop is located inside a dipole spectrometer magnet in close proximity to straw drift chambers and intercepts a high-intensity neutral hadron beam. The design process, involving both Monte Carlo simulations and beam tests of alternative beam-stop shielding arrangements, had the goal of minimizing the leakage of particles from the beam stop and the resulting hit rates in detectors, while preserving maximum acceptance for events of interest. The beam tests consisted of measurements of rates in drift chambers, scintilation counter hodoscopes, a gas threshold Cherenkov counter, and a lead glass array. Measurements were also made with a set of specialized detectors which were sensitive to low-energy neutrons, photons, and charged particles. Comparisons are made between these measurements and a detailed Monte Carlo simulation.Comment: 39 pages, 14 figures, submitted to Nuclear Instruments and Method