Search

The final oscillation analysis of the complete set of data collected by CHORUS in the years 1994-1997 is presented. Reconstruction algorithms of data extracted by electronic detectors were improved and the data recorded in the emulsion target were analysed by new automated scanning systems, allowing the use of a new method for event reconstruction in emulsion. CHORUS has applied these new techniques to the sample of 1996-1997 events for which no muons were observed in the electronic detectors. Combining the new sample with the data analysed in previous papers, the overall sensitivity of the experiment to the ?? appearance is thus improved. In a two-neutrino mixing scheme, a 90% C.L. upper limit of sin2 2 ?µ ? < 4.4 × 10-4 is set for large ? m2, improving by a factor 1.5 the previously published CHORUS result. © 2007 Elsevier B.V. All rights reserved. Bundesministerium für Bildung und Forschung: 05 7MS12P, 05 6BU11P Grant Foundation: KRF-2003-005-C00014 Promotion and Mutual Aid Corporation for Private Schools of Japan CERN Israel Science Foundation: 328/94 Brussels Instituut voor Milieubeheer Istituto Nazionale di Fisica Nucleare Foundation for Fundamental Research on Matter Korean Foundation for Cancer Research Walter Burke Institute for Theoretical Physics We gratefully acknowledge the help and support of the neutrino beam staff and of the numerous technical collaborators who contributed to the detector construction, operation, emulsion pouring, development, and scanning. The experiment has been made possible by grants from the Institut Interuniversitaire des Sciences Nucléaires and the Interuniversitair Instituut voor Kernwetenschappen (Belgium), the Israel Science Foundation (grant 328/94) and the Technion Vice President Fund for the Promotion of Research (Israel), CERN (Geneva, Switzerland), the German Bundesministerium für Bildung und Forschung (contract numbers 05 6BU11P and 05 7MS12P) (Germany), the Institute of Theoretical and Experimental Physics (Moscow, Russia), the Istituto Nazionale di Fisica Nucleare (Italy), the Promotion and Mutual Aid Corporation for Private Schools of Japan and Japan Society for the Promotion of Science (Japan), the Korea Research Foundation Grant (KRF-2003-005-C00014) (Republic of Korea), the Foundation for Fundamental Research on Matter FOM and the National Scientific Research Organization NWO (The Netherlands), and the Scientific and Technical Research Council of Turkey (Turkey). We gratefully acknowledge their support.

The ALEPH detector at LEP has been used to measure the momentum spectrum and charge ratio of vertical cosmic ray muons underground. The sea-level cosmic ray muon spectrum for momenta up to 2.5 TeV/c has been obtained by correcting for the overburden of 320 meter water equivalent (mwe). The results are compared with Monte Carlo models for air shower development in the atmosphere. From the analysis of the spectrum the total flux and the spectral index of the cosmic ray primaries is inferred. The charge ratio suggests a dominantly light composition of cosmic ray primaries with energies up to 10^15 eV., 4 pages, 3 figures, 1 table

CosmoALEPH is an experiment operated in conjunction with the ALEPH detector. The ALEPH experiment took data from 1989 until the year 2000 at the Large Electron Positron Collider (LEP) at CERN. It provides, among others, high resolution tracking and calorimetry. CosmoALEPH used this e + e − detector for cosmic ray studies. In addition, six scintillator telescopes were installed in the ALEPH pit and the LEP tunnel. The whole experiment operated underground at a vertical depth of 320 meter water equivalent. Data from ALEPH and the scintillator telescopes provide informaton on the lateral distribution of energetic cosmic ray muons in extensive air showers. The decoherence curve of these remnant air shower muons is sensitive to the chemical composition of primary cosmic rays and to the interaction characteristics of energetic hadrons in the atmosphere. An attempt is made to extract the various interdependencies in describing the propagation of primary and secondary cosmic rays through the atmosphere and the rock overburden, and comparing the data with results from Monte Carlo (MC) calculations. Results on the multiplicity distributions of remnant air shower muons in ALEPH are also compared with expectations based on MC simulations. Data on the cosmic ray muon spectrum and charge ratio up to momenta of 3 TeV/c as obtained with the time projection chamber in ALEPH's strong magnetic field are presented. The large number of events also allowed to unambiguously observe muon tridents and to estimate the cross section for this process.

The ALEPH detector at LEP has been supplemented with five scintillator telescopes to measure the muon component of cosmic ray air showers underground. The emphasis of the present analysis of a new data set is to measure coincidences over distances up to about 1 km which are sensitive to the forward production of hadronic interactions and the chemical composition of primary cosmic rays in the energy range around 1015 eV. First results indicate that the observed decoherence curve of muons is compatible with a light primary composition and the arrival directions of muons show no obvious clustering in galactic coordinates.

Part of the neutrino events collected in 1994-1995 by the CHORUS experiment has been analysed. A search was performed for ντ charged current interactions followed by the τ lepton decay into a single charged negative hadron, a possible indication for νμ→ντ oscillation. A sample of 6844 events without an identified muon has been located in the emulsion target. Within the selection criteria, no τ− candidate has been found. Combining this result with the one from the search for ντ interactions using the muonic decay mode (36 182 events with an identified muon), a 90% C.L. limit on the mixing angle sin22θμτ

The ALEPH experiment at the LEP e+e− storage ring at CERN has been used to measure the momentum spectrum of cosmic ray muons. ALEPH is located at a vertical depth of 320 m.w.e. underground close to the Jura mountains. The high resolution of the time projection chamber (TPC) of ALEPH allows to reconstruct muon tracks with momenta up to the TeV region. The measured muon momentum spectrum and the charge ratio in the range from 80 to 2500 GeV are presented. After corrections for energy loss in the overburden the sea level muon spectrum at nearly vertical incidence is obtained. The experimental data are compared to theoretical expectations and results from other experiments.

Data from a dedicated cosmic ray run of the ALEPH detector were used in a study of muon trident production, i.e., muon pairs produced by muons. Here the overburden and the calorimeters are the target materials while the ALEPH time projection chamber provides the momentum measurements. A theoretical estimate of the muon trident cross section is obtained by developing a Monte Carlo simulation for muon propagation in the overburden and the detector. Two muon trident candidates were found to match the expected theoretical pattern. The observed production rate implies that the nuclear form factor cannot be neglected for muon tridents.

The ALEPH detector at LEP has been supplemented with five scintillator stations to measure the muon component of cosmic ray showers underground. We report the measurements of coincidences over distances up to about 1 km which are sensitive to the forward production of hadronic interactions and the chemical composition of primary cosmic rays in the energy range around 10{sup 15} eV. The results are compared to the expectations obtained from Monte Carlo simulation. Our results indicate that the observed decoherence curve of muons is compatible with a light primary composition. In addition, the arrival times of muons underground as measured with scintillator stations allow to reconstruct the muon arrival directions in 3-fold coincidence events. These results are compared to shower simulations.