Ref HAL: in2p3-00124806_v1
Ref Arxiv: astro-ph/0607569
DOI: 10.1051/0004-6361:20054732
Ref. & Cit.: NASA ADS
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54 citations
Résumé:

The extreme synchrotron BL Lac object H2356-309, located at a redshift of z = 0.165, was observed from June to December 2004 with a total exposure of approx. 40 h live-time with the H.E.S.S. (High Energy Stereoscopic System) array of atmospheric-Cherenkov telescopes (ACTs). Analysis of this data set yields, for the first time, a strong excess of 453 gamma-rays (10 standard deviations above background) from H2356-309, corresponding to an observed integral flux above 200 GeV of I(>200GeV) = (4.1+-0.5) 10^12 cm^-2.s^-1 (statistical error only). The differential energy spectrum of the source between 200 GeV and 1.3 TeV is well-described by a power law with a normalisation (at 1 TeV) of N_0 = (3.00 +- 0.80_stat +- 0.31_sys) 10^-13 cm^-2.s^-1.TeV^-1 and a photon index of Gamma = 3.09 +- 0.24_stat +- 0.10_sys. H2356-309 is one of the most distant BL Lac objects detected at very-high-energy gamma-rays so far. Results from simultaneous observations from ROTSE-III (optical), RXTE (X-rays) and NRT (radio) are also included and used together with the H.E.S.S. data to constrain a single-zone homogeneous synchrotron self-Compton (SSC) model. This model provides an adequate fit to the H.E.S.S. data when using a reasonable set of model parameters.

Commentaires: 7 pages, 4 figures, accepted for publication in Astronomy and Astrophysics (05/07/2006)

Ref HAL: in2p3-00025465_v1
Ref Arxiv: astro-ph/0511678
DOI: 10.1051/0004-6361:20054279
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
253 citations
Résumé:

We present results from deep observations of the Galactic shell-type supernova remnant (SNR) RX J1713.7-3946 (also known as G347.3-0.5) conducted with the complete H.E.S.S. array in 2004. Detailed morphological and spatially resolved spectral studies reveal the very-high-energy (VHE -- Energies E > 100 GeV) gamma-ray aspects of this object with unprecedented precision. Since this is the first in-depth analysis of an extended VHE gamma-ray source, we present a thorough discussion of our methodology and investigations of possible sources of systematic errors. Gamma rays are detected throughout the whole SNR. The emission is found to resemble a shell structure with increased fluxes from the western and northwestern parts. The differential gamma-ray spectrum of the whole SNR is measured over more than two orders of magnitude, from 190 GeV to 40 TeV, and is rather hard with indications for a deviation from a pure power law at high energies. Spectra have also been determined for spatially separated regions of RX J1713.7-3946. The flux values vary by more than a factor of two, but no significant change in spectral shape is found. There is a striking correlation between the X-ray and the gamma-ray image. Radial profiles in both wavelength regimes reveal the same shape almost everywhere in the region of the SNR. The VHE gamma-ray emission of RX J1713.7-3946 is phenomenologically discussed for two scenarios, one where the gamma rays are produced by VHE electrons via Inverse Compton scattering and one where the gamma rays are due to neutral pion decay from proton-proton interactions. In conjunction with multi-wavelength considerations, the latter case is favoured. However, no decisive conclusions can yet be drawn regarding the parent particle population dominantly responsible for the gamma-ray emission from RX J1713.7-3946.

Commentaires: 20 pages, 20 figures (low resolution), Accepted for publication in A&A - Revision 1: Added reference to Section 4.2. Added sentence to acknowledgements

Ref HAL: hal-00078988_v1
Ref Arxiv: astro-ph/0603725
DOI: 10.1086/527524
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
17 citations

Ref HAL: in2p3-00021799_v1
DOI: 10.1016/j.physletb.2004.10.057
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5 citations
Résumé:

The cross sections for single vector boson production in the Wenu and Zee channels are measured from the data collected by the ALEPH detector at LEP for centre-of-mass energies between 183 and 209 GeV. These data correspond to a total integrated luminosity of 683 pb-1. Single-W production is studied in both hadronic and leptonic decay channels. Hadronic and dimuon decays are used for single-Z production. The measured cross sections agree with the Standard Model predictions.

Commentaires: 05 ALEPH

Ref HAL: in2p3-00021836_v1
DOI: 10.1016/j.physletb.2004.11.048
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14 citations
Résumé:

Two-Particle correlations in pp, pbarpbar and K0sK0s pairs have been studied in hadronic Z decays recorded at LEP with the ALEPH detector. The correlations were measured as a function of the four-momentum difference Q of the pair. For pp, pbarpbar pairs a depletion of events is observed in the region Q < 3 GeV, and for K0sK0s pairs an enhancement of events is observed in the region Q < 0.5 GeV. These features are consistent with expectations from Fermi-Dirac and Bose-Einstein statistics, respectively.

Ref HAL: in2p3-00024366_v1
Ref Arxiv: hep-ex/0506072
DOI: 10.1016/j.physrep.2005.06.007
Ref. & Cit.: NASA ADS
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278 citations
Résumé:

The full LEP-1 data set collected with the ALEPH detector at the $Z$ pole during 1991-1995 is analysed in order to measure the $\tau$ decay branching fractions. Extensive systematic studies are performed, in order to match the large statistics of the data sample corresponding to over 300 000 measured and identified $\tau$ decays. Branching fractions are obtained for the two leptonic channels and eleven hadronic channels defined by their respective numbers of charged particles and $\pi^0$'s. Using previously published ALEPH results on final states with charged and neutral kaons, corrections are applied to the hadronic channels to derive branching ratios for exclusive final states without kaons. Thus the analyses of the full LEP-1 ALEPH data are combined to yield a complete description of $\tau$ decays, encompassing 22 non-strange and 11 strange hadronic modes. Some physics implications of the results are given, in particular related to universality in the leptonic charged weak current, isospin invariance in $a_1$ decays, and the separation of vector and axial-vector components of the total hadronic rate. Finally, spectral functions are determined for the dominant hadronic modes and updates are given for several analyses. These include: tests of isospin invariance between the weak charged and electromagnetic hadronic currents, fits of the $\rho$ resonance lineshape, and a QCD analysis of the nonstrange hadronic decays using spectral moments, yielding the value $\alpha_s(m^2_\tau) = 0.340 \pm 0.005_{\rm exp} \pm 0.014_{\rm th}$. The evolution to the $Z$ mass scale yields $\alpha_s(M_Z^2) = 0.1209 \pm 0.0018$. This value agrees well with the direct determination from the $Z$ width and provides the most accurate test to date of asymptotic freedom in the QCD gauge theory

Commentaires: 139 pages, 75 figures, submitted to Physics Reports

Ref HAL: in2p3-00023825_v1
DOI: 10.1016/j.physletb.2005.03.058
Exporter : BibTex | endNote
56 citations
Résumé:

Triple gauge-boson couplings WWgamma and WWZ involving single-photon, single-W and W-pair production are determined using data samples collected at LEP with the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. The integrated luminosity used is 700 pb-1 for the single-photon measurement and 683 pb-1 for the W channels. Restricting the measurement to C- and P- conserving terms and applying local SU(2)xU(1) gauge invariance, the measured values of the parameters g1z, kappa_gamma and lambda_gamma are: g1z = 1.001 +/- 0.027(stat.) +/- 0.013(syst.) kappa_gamma = 0.971 +/- 0.055(stat.) +/- 0.030(syst.) lambda_gamma = -0.012 +/- 0.027(stat.) +/- 0.011(syst.) for single-parameter fits, where the two other parameters are fixed to their Standard Model values. Results are also presented for the cases where two or all three couplings are allowed to vary. An additional analysis using W-pair events is performed to measure the unconstrained real and imaginary parts of all 14 triple gauge-boson couplings and to perform an indirect search for a techni-rho resonance. No deviations from the Standard Model expectations are observed and the lower limit on the techni-rho mass is set to 600 GeV/c2 at 95% confidence level.

Commentaires: 04 ALEPH