arXiv subjects

Michel Davier

Publications and source records attributed to Michel Davier.

26 records · Page 2Linked to original sources

arXiv2003

Spectral functions from Hadronic Tau Decays and QCD

Hadronic decays of the $τ$ lepton provide a clean environment to study hadron dynamics in an energy regime dominated by resonances, with the interesting information captured in the spectral functions. Recent results from ALEPH on exclusive channels are presented, with some emphasis on the $π\piz$ final state which plays a crucial role for the determination of the hadronic contribution to the muon anomalous magnetic moment. Inclusive spectral functions are the basis for QCD analyses, delivering an accurate determination of the strong coupling constant, quantitative information on nonperturbative contributions and a measurement of the mass of the strange quark.

hep-ex↗

arXiv2003

An elliptical tiling method to generate a 2-dimensional set of templates for gravitational wave search

Searching for a signal depending on unknown parameters in a noisy background with matched filtering techniques always requires an analysis of the data with several templates in parallel in order to ensure a proper match between the filter and the real waveform. The key feature of such an implementation is the design of the filter bank which must be small to limit the computational cost while keeping the detection efficiency as high as possible. This paper presents a geometrical method which allows one to cover the corresponding physical parameter space by a set of ellipses, each of them being associated to a given template. After the description of the main characteristics of the algorithm, the method is applied in the field of gravitational wave (GW) data analysis, for the search of damped sine signals. Such waveforms are expected to be produced during the de-excitation phase of black holes -- the so-called 'ringdown' signals -- and are also encountered in some numerically computed supernova signals.

gr-qc↗

arXiv2002

Measurement of Branching Fractions in Tau Decays

Full LEP-I data collected by the ALEPH detector during 1991-1995 running are analyzed in order to measure the $τ$ decay branching fractions. The analysis follows the global method used in the published study based on 1991-1993 data, with several improvements, especially concerning the treatment of photons and $π^0$'s. Extensive systematic studies are performed, in order to match the large statistics of the data sample corresponding to 327148 measured and identified $τ$ decays. Preliminary values for the branching fractions are obtained for the 2 leptonic channels and 11 hadronic channels defined by their respective numbers of charged particles and $π^0$'s. Using previously published ALEPH results on final states with charged and neutral kaons, corrections are applied so that branching ratios for exclusive final states without kaons are derived. Some physics implications of the results are given, in particular concerning 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.

hep-ex↗

arXiv2001

Detection in coincidence of gravitational wave bursts with a network of interferometric detectors (I): Geometric acceptance and timing

Detecting gravitational wave bursts (characterised by short durations and poorly modelled waveforms) requires to have coincidences between several interferometric detectors in order to reject non-stationary noise events. As the wave amplitude seen in a detector depends on its location with respect to the source direction and as the signal to noise ratio of these bursts are expected to be low, coincidences between antennas may not be so likely. This paper investigates this question from a statistical point of view by using a simple model of a network of detectors; it also estimates the timing precision of a detection in an interferometer which is an important issue for the reconstruction of the source location, based on time delays.

gr-qc↗

arXiv2000

An efficient filter for detecting gravitational wave bursts in interferometric detectors

Typical sources of gravitational wave bursts are supernovae, for which no accurate models exist. This calls for search methods with high efficiency and robustness to be used in the data analysis of foreseen interferometric detectors. A set of such filters is designed to detect gravitational wave burst signals. We first present filters based on the linear fit of whitened data to short straight lines in a given time window and combine them in a non linear filter named ALF. We study the performances and efficiencies of these filters, with the help of a catalogue of simulated supernova signals. The ALF filter is the most performant and most efficient of all filters. Its performance reaches about 80% of the Optimal Filter performance designed for the same signals. Such a filter could be implemented as an online trigger (dedicated to detect bursts of unknown waveform) in interferometric detectors of gravitational waves.

gr-qc↗

arXiv1999

Hadronic τdecays and QCD

Hadronic decays of the $τ$ lepton provide a clean source to study hadron dynamics in an energy regime dominated by resonances, with the interesting information captured in the spectral functions. Recent results on exclusive channels are reviewed. Inclusive spectral functions are the basis for QCD analyses, delivering an accurate determination of the strong coupling constant and quantitative information on nonperturbative contributions. Strange decays yield a determination of the strange quark mass.

hep-ex↗

arXiv1998

Evaluation of $α(M_{\rm Z}^2)$ and $(g-2)_μ$

This talk summarizes the recent developments in the evaluation of the leading order hadronic contributions to the running of the QED fine structure constant $α(s)$, at $s=M_{\rm Z}^2$, and to the anomalous magnetic moment of the muon $(g-2)_μ$. The accuracy of the theoretical prediction of these observables is limited by the uncertainties on the hadronic contributions. Significant improvement has been achieved in a series of new analyses which is presented historically in three steps: (I), use of $τ$ spectral functions in addition to $e^+e^-$ cross sections, (II), extended use of perturbative QCD and (III), application of QCD sum rule techniques. The most precise values obtained are: $Δα_{\rm had}(M_{\rm Z}^2)$, $=(276.3\pm1.6)\times10^{-4}$, yielding $α^{-1}(M_{\rm Z}^2)=128.933\pm0.021$, and $a_μ^{\rm had}=(692.4\pm6.2)\times 10^{-10}$ with which one finds for the complete Standard Model prediction $a_μ^{\rm SM}=(11 659 159.6\pm6.7)\times10^{-10}$. For the electron $(g-2)_e$, the hadronic contribution is $a_e^{\rm had}=(187.5\pm1.8)\times 10^{-14}$.

hep-ph↗

arXiv1997

Improved Determination of alpha_QED(M_Z^2) and the Anomalous Magnetic Moment of the Muon

We reevaluate the hadronic contribution to the running of the QED fine structure constant alpha(s) at s = M_Z^2. We use data from e+e- annihilation and tau decays at low energy and at the qq-bar thresholds, where resonances occur. Using so-called spectral moments and the Operator Product Expansion (OPE), it is shown that a reliable theoretical prediction of the hadronic production rate R(s) is available at relatively low energies. Its application improves significantly the precision on the hadronic vacuum polarization contribution. We obtain delta_alpha^had = (277.8 +/- 2.6) x 10^-4 yielding alpha^-1(M_Z^2) = 128.923 +/- 0.036$. Inserting this value in a global electroweak fit using current experimental input, we constrain the mass of the Standard Model Higgs boson to be M_Higgs = (129 +103 -62) GeV. Analogously, we improve the precision of the hadronic contribution to the anomalous magnetic moment of the muon for which we obtain a_mu^had = (695.1 +/- 7.5) x 10^-10.

hep-ph↗