[show abstract][hide abstract] ABSTRACT: We present results from a study of hadronic event structure in high energy e+e− interactions using the L3 detector at LEP. A new class of event shape distributions are measured at and above the Z boson pole for light quark (u, d, s, c) flavours. Energy flow correlations are studied for all hadronic events. Next-to-leading-log QCD calculations and QCD models with improved leading-log approximations are compared to data and good agreement is found at the Z-pole whereas some discrepancies are observed at higher centre-of-mass energies.
Journal of High Energy Physics 08/2013; 2011(10). · 5.62 Impact Factor
[show abstract][hide abstract] ABSTRACT: We describe a new underground laboratory, namely LAFARA (for "LAboratoire de mesure des FAibles RAdioactivités"), that was recently created in the French Pyrénées. This laboratory is primarily designed to analyze environmental samples that display low radioactivity levels using gamma-ray spectrometry. Two high-purity germanium detectors were placed under 85 m of rock (ca. 215 m water equivalent) in the tunnel of Ferrières (Ariège, France). The background is thus reduced by a factor of ∼20 in comparison to above-ground laboratories. Both detectors are fully equipped so that the samples can be analyzed in an automatic mode without requiring permanent presence of a technician in the laboratory. Auto-samplers (twenty positions) and systems to fill liquid nitrogen automatically provide one month of autonomy to the spectrometers. The LAFARA facility allows us to develop new applications in the field of environmental sciences based on the use of natural radionuclides present at low levels in the environment. As an illustration, we present two of these applications: i) dating of marine sediments using the decay of (226)Ra in sedimentary barite (BaSO(4)), ii) determination of (227)Ac ((231)Pa) activities in marine sediment cores.
Journal of environmental radioactivity 11/2012; 116C:152-158. · 1.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by
the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined
for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no
significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper
bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number
of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large
exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses
of neutral Higgs bosons.
European Physical Journal C 04/2012; 47(3):547-587. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: Bose–Einstein correlations of pairs of identical charged pions produced in hadronic Z decays are analyzed in terms of various
parametrizations. A good description is achieved using a Lévy stable distribution in conjunction with a model where a particle’s
momentum is correlated with its space–time point of production, the τ-model. Using this description and the measured rapidity and transverse momentum distributions, the space–time evolution of
particle emission in two-jet events is reconstructed. However, the elongation of the particle emission region previously observed
is not accommodated in the τ-model, and this is investigated using an adhoc modification.
European Physical Journal C 04/2012; 71(5):1-25. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: The variety of isotopes in cosmic rays allows us to study different aspects of the processes that cosmic rays undergo between the time they are produced and the time of their arrival in the heliosphere. In this paper, we present measurements of the isotopic ratios 2H/4He, 3He/4He, 6Li/7Li, 7Be/(9Be+10Be), and 10B/11B in the range 0.2-1.4 GeV of kinetic energy per nucleon. The measurements are based on the data collected by the Alpha Magnetic Spectrometer, AMS-01, during the STS-91 flight in 1998 June.
The Astrophysical Journal 07/2011; 736(2):105. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report vertical profiles of radium-226 (226Ra) concentrations determined in seawater and suspended particles collected in the North-West Pacific using Multi Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Dissolved 226Ra concentrations were determined in small size water samples (between 110 and 250ml volume) with a precision usually better than 5% (internal error, two standard error, 2σm) using a chemical protocol slightly modified compared to previous studies that provides a chemical recovery of 90%. The 226Ra activities thus obtained are in good agreement with the 226Ra activities determined using low-background gamma spectrometry. In this work, we report the first 226Ra activities determined in marine suspended particles using MC-ICP-MS. We thus show that this method is very useful to determine 226Ra concentrations in suspended particles that have been poorly studied up to now because they display very low 226Ra activities (i.e. two orders of magnitude lower than the 226Ra activity in seawater). Such a sensitive method can thus be used to build high-resolution vertical profiles of dissolved and particulate 226Ra activities, which would allow us to better understand the impact of biology on the oceanic Ra cycle.
Marine Chemistry - MAR CHEM. 01/2011; 126(1):132-138.
[show abstract][hide abstract] ABSTRACT: Measurement of the chemical and isotopic composition of cosmic rays is essential for the precise understanding of their propagation in the galaxy. While the model parameters are mainly determined using the B/C ratio, the study of extended sets of ratios can provide stronger constraints on the propagation models. In this paper, the relative abundances of light-nuclei lithium, beryllium, boron, and carbon are presented. The secondary-to-primary ratios Li/C, Be/C, and B/C have been measured in the kinetic energy range 0.35-45 GeV nucleon–1. The isotopic ratio 7Li/6Li is also determined in the magnetic rigidity interval 2.5-6.3 GV. The secondary-to-secondary ratios Li/Be, Li/B, and Be/B are also reported. These measurements are based on the data collected by the Alpha Magnetic Spectrometer AMS-01 during the STS-91 space shuttle flight in 1998 June. Our experimental results are in substantial agreement with other measurements, where they exist. We describe our light-nuclei data with a diffusive-reacceleration model. A 10%-15% overproduction of Be is found in the model predictions and can be attributed to uncertainties in the production cross-section data.
The Astrophysical Journal 11/2010; 724(1):329. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: a b s t r a c t The Alpha Magnetic Spectrometer is a large acceptance cosmic-ray detector ð0:5 m 2 srÞ designed to operate at an altitude of 400 km on the International Space Station. The AMS-02 silicon tracker contains 2264 silicon microstrip sensors (total active area 6:75 m 2). The internal alignment parameters of the assembled tracker have been determined on the ground with cosmic-ray muons. The alignment procedure is described and results for the alignment precision and position resolution are reported. & 2009 Elsevier B.V. All rights reserved.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: a b s t r a c t The Alpha Magnetic Spectrometer is designed for a long duration measurement of the cosmic-ray spectra at an altitude of 400 km. The particle rigidity and specific energy loss are measured by a silicon tracker located in a 0.8 T field. Ground results for the position resolution, detection efficiency and charge determination for singly and doubly charged relativistic particles are presented and discussed in the context of the spaceborne detector.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2008; · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: Context. Primary cosmic rays experience multiple deflections in the non-uniform galactic and heliospheric magnetic fields which may generate anisotropies. Aims. A study of anisotropies in the energy range between 100 and 500 GeV is performed. This energy range is not yet well explored. Methods. The L3 detector at the CERN electron-positron collider, LEP, is used for a study of the angular distribution of atmospheric muons with energies above 20 GeV. This distribution is used to investigate the isotropy of the time-dependent intensity of the primary cosmic-ray flux with a Fourier analysis. Results. A small deviation from isotropy at energies around 200 GeV is observed for the second harmonics at the solar frequency. No sidereal anisotropy is found at a level above 10(-4). The measurements were performed in the years 1999 and 2000.
Astronomy and Astrophysics 03/2008; 488:1093-1100. · 5.08 Impact Factor