T. Hebbeker

A precise determination of the electroweak mixing angle from semi-leptonic neutrino scattering

Abstract The cross section ratio of neutral-current and charged-current semi-leptonic interactions of muon-neutrinos on isoscalar nuclei has been measured with the result: R v =0.3093±0.0031 for hadronic energy larger than 4 GeV. From this ratio, the electroweak mixing angle is determined to be sin 2 θ w =0.236+0.012( m c −1.5)±0.005 (exp.)±0.003 (theor.), where m c is the charm-quark mass in GeV/ c 2 .

A search for decays of heavy neutrinos in the mass range 0.5–2.8 GeV

A search for decays of heavy neutrinos was conducted by the CHARM Collaboration in a prompt neutrino beam produced by dumping 400 GeV protons in a Cu target, and in the CERN wide-band neutrino beam produced by 400 GeV primary protons. No candidate event was found. In the beam-dump experiment heavy neutrinos have been assumed to be produced by mixing in charmed D meson decays. Neutrinos decaying into e+e−ve, μ+e−vμ, and μ+μ−vμ were searched for. Limits of |Uei|2, |Uμi|2 < 10−7 were obtained for neutrino masses around 1.5 GeV. In the wide-band experiment heavy neutrinos were assumed to be produced by neutral-current neutrino interactions in the CHARM calorimeter. Here a search was made for neutrinos decaying into a μ and hadrons. This experiment is sensitive to decays of neutrinos with mass in the range 0.5–2.8 GeV with limits of |Uμi|2 < 3 × 10−4 for masses around 2.5 GeV. These measurements extend our previous results in the mass range 10–400 MeV.

A Precise Determination of the Electroweak Mixing Angle from Semileptonic Neutrino Scattering

The cross-section ratio of neutral-current and charged-current semileptonic interactions of muon-neutrinos on isoscalar nuclei has been measured with the result:Rv=0.3093±0.0031 for hadronic energy larger than 4 GeV. From this ratio we determined the electroweak mixing angle sin2θW, wheremc is the charm-quark mass in GeV/c2. Comparison with direct measurements ofmw andmz determines the radiative shift of the intermediate boson mass Δr=0.077±0.025(exp.)±0.038(syst.), in agreement with the prediction. Assuming the validity of the electroweak standard theory we determined ϱ=0.990−0.013(mc−1.5)±0.009(exp.)±0.003(theor.).

Search for axion-like particle production in 400 GeV proton-copper interactions

Abstract A search for axion-like particles was performed at the 400 GeV proton beam-dump experiment at CERN. Exploring an empty decay region of 35 m length and 9 m 2 cross section, we searched for decays of neutral and penetrating scalar particles into a pair of photons, electrons or muons. No evidence for the existence for such particles was found in this experiment. Limits are quoted as a function of the mass and of the model independent decay constant of axions.

A Compilation of High Energy Atmospheric Muon Data at Sea Level

Abstract We collect and combine all published data on the vertical atmospheric muon flux and the muon charge ratio for muon momenta above 10 GeV. At sea level the world average of the momentum spectra agrees with the flux calculated by Phys. Rev. D 58 (1998) 054001 within 15%. The experimental accuracy varies from 7% at 10 GeV to 13% at 1 TeV. The ratio of fluxes of positive to negative muons is found to be constant, at a value of 1.268, with relative uncertainties increasing from approximately 1% at low momenta to about 6% at 300 GeV.

The L3+C detector, a unique tool-set to study cosmic rays

AbstractThe L3 detector at the CERN electron–positron collider, LEP, has been employed for the study of cosmic ray muons.The muon spectrometer of L3 consists of a set of high-precision drift chambers installed inside a magnet with avolume of about 1000 m 3 and a field of 0:5T: Muon momenta are measured with a resolution of a few percentat 50 GeV: The detector is located under 30 m of overburden. A scintillator air shower array of 54 m by 30 mis installed on the roof of the surface hall above L3 in order to estimate the energy and the core position of theshower associated with a sample of detected muons. Thanks to the unique properties of the L3þC detector, muonresearch topics relevant to various current problems in cosmic ray and particle astrophysics can be studied. r 2002Elsevier Science B.V. All rights reserved. PACS: 95.55.Vj; 98.70.Sa; 96.40.Tv; 95.85.RyKeywords: L3+C detector; Cosmic rays; Muon spectrum; Astroparticle physics 1. IntroductionThe L3þ C experiment (Figs. 1 and 2), installedat the Large Electron Positron collider (LEP) atCERN, Geneva, consists of two major parts:firstly, below ground, the L3 muon spectrometer[1], which is comprised of a large 0:5 T magnetwith a volume of 1000 m

Experimental results on neutrino-electron scattering

A determination of sin2θw based on measurements of elastic scattering of muon-neutrinos and muon-anti-neutrinos on atomic electrons is described. These purely leptonic processes were studied using the CHARM calorimeter exposed to neutrino and antineutrino wide-band beams at the CERN super proton synchrotron. A total of 83±16 neutrino-electron and 112±21 antineutrino-electron events have been detected. From the measurement of the ratio of muon-neutrino and muon-antineutrino cross-sections a value of sin2θw=0.211±0.037 was obtained.

A search for oscillations of muon neutrinos in an experiment with L/E ≅0.7 km/GeV

Abstract A low-energy muon neutrino beam was used to illuminate two similar fine-grained neutrino detectors placed at 123 m and 903 m from the beginning of the neutrino source. The fiducial masses of the “close” and the “far” detector were about 36 tons and 120 tons respectively. The average energy of the selected neutrino events was 1.5 GeV. Data were recorded for an integrated flux of about 1019 protons. Quasielastic charged current events initiated by νes have been searched for and an upper limit of 2.7%, at 90% confidence level, is obtained for the fraction of νμs transformed into νes. For complete mixing this correspnds to a limit Δm2 ⩽ 0.20 eV2 for the transition νμ → νe and to a minimum value of the mixing parameter sin22θ = 0.04. In the same data sample we compared the rates in the two detectors of νμ-initiated charged current events, mainly of quasielastic type: we conclude that oscillations of νμs to ντs, and possibly heavier neutrinos, do not appear. For complete mixing the limit in this case is Δm2 ⩽ 0.29 eV2.

The L3 energy trigger

Abstract The L3 first-level energy trigger is based on energy measurements in electromagnetic and hadronic calorimeters and in luminosity monitors. The information from these detectors is evaluated and a decision is taken in about 20 μs (the time between two bunch crossings in LEP is 22 μs). This trigger makes use of 300 CAMAC modules: an arithmetic logic unit (ALU), a BUS multiplexer (BS), a memory lookup table (MLU), a data stack (DS) and a fast encoding and readout ADC (FERA), each of them performing dedicated functions. The data are transmitted via front-panel ECL buses. The CAMAC data-way is used only for initialization and checking purposes. The system operates synchronously with a period of 60 ns.

Parametrization of Proton Structure Functions

Abstract We present a parametrization of the parton densities as derived from the data collected by the CHARM Collaboration in the wide band beam neutrino and antineutrino weak charged-current interactions. They are rescaled to the proton and calculated at a reference Q 2 value of 10 GeV 2 including the next-to-leading order corrections and imposing the Gross-Llewellyn Smith and the momentum sum rules.