316 research outputs found
Global P- and S-wave tomography from finite-frequency traveltime residual measurements
There are two main ways to improve the resolution of tomographic images: building larger and higher quality datasets, and using better imaging theories, such as finite frequency theory or waveform inversion, instead of the more commonly used ray theory. A first step toward improving the resolution of global tomographic models is thus to construct a seismological database adapted to finite-frequency tomography or waveform inversion. We present a global dataset of finite frequency travel time residuals. These measurements were obtained by cross-correlating observed and synthetic waveforms in several frequency bands. We exploit seismograms at significantly shorter periods than in other recent comparable works. We compute Green's functions with the GEMINI method and convolve them with high-frequency source-time functions. These source-time functions are inverted, along with focal depths, with a simulated annealing approach. We measure travel time residuals on different P and S phases. We check the quality of our global database by performing preliminary tomographic inversions using ray theory. We use the subset of measurements performed in the 0.0725-Hz frequency range, combined to ISC travel times, to build tomographic models for both P and S velocity anomalies. Resulting models are presented and compared to recently published global tomographic models, and some implications for finite frequency effects and physical properties of the deep Earth are discussed
de Branges-Rovnyak spaces: basics and theory
For a contractive analytic operator-valued function on the unit disk
, de Branges and Rovnyak associate a Hilbert space of analytic
functions and related extension space
consisting of pairs of analytic functions on the unit disk . This
survey describes three equivalent formulations (the original geometric de
Branges-Rovnyak definition, the Toeplitz operator characterization, and the
characterization as a reproducing kernel Hilbert space) of the de
Branges-Rovnyak space , as well as its role as the underlying
Hilbert space for the modeling of completely non-isometric Hilbert-space
contraction operators. Also examined is the extension of these ideas to handle
the modeling of the more general class of completely nonunitary contraction
operators, where the more general two-component de Branges-Rovnyak model space
and associated overlapping spaces play key roles. Connections
with other function theory problems and applications are also discussed. More
recent applications to a variety of subsequent applications are given in a
companion survey article
The dependence of the anomalous J/psi suppression on the number of participant nucleons
The observation of an anomalous J/psi suppression in Pb-Pb collisions by the NA50 Collaboration can be considered as the most striking indication for the deconfinement of quarks and gluons at SPS energies. In this Letter, we determine the J/psi suppression pattern as a function of the forward hadronic energy E-ZDC measured in a Zero Degree Calorimeter (ZDC). The direct connection between EZDC and the geometry of the collision allows us to calculate, within a Glauber approach, the precise relation between the number of participant nucleons N-part and E-ZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/psi suppression as a function of the number of participants. (C) 2001 Elsevier Science B.V. All rights reserved.info:eu-repo/semantics/publishedVersio
Centrality Behaviour of J/ Production in Na50
The J/ production in 158 A GeV Pb-Pb interactions is studied, in the
dimuon decay channel, as a function of centrality, as measured with the
electromagnetic or with the very forward calorimeters. After a first sharp
variation at mid centrality, both patterns continue to fall down and exhibit a
curvature change at high centrality values. This trend excludes any
conventional hadronic model and is in agreement with a deconfined quark-gluon
phase scenario. We report also preliminary results on the measured charged
multiplicity, as given by a dedicated detector.Comment: 5 pages, 7 figures (in eps) talk given at XXXI International
Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL
http://ismd31.ccnu.edu.cn
Scaling of charged particle multiplicity in Pb-Pb collisions at SPS energies
The charged particle multiplicity distribution has been measured by the NA50 experiment in Pb--Pb collisions at the CERN SPS. Measurements were done at incident energies of 40 and 158 GeV per nucleon over a broad impact parameter range. The multiplicity distributions are studied as a function of centrality using the number of participating nucleons (), or the number of binary nucleon--nucleon collisions (). Their values at midrapidity exhibit a power law scaling behaviour given by and at 158 GeV. Compatible results are found for the scaling behaviour at 40 GeV. The width of the distributions is larger at 158 than at 40 GeV/nucleon and decreases slightly with centrality at both energies. Our results are compared to similar studies performed by other experiments both at the CERN SPS and at RHIC.
Anomalous suppression in Pb-Pb interactions at 158 GeV per nucleon
The Drell-Yan and J/psi cross-sections measured in Pb-Pb collisions are compared with the values extrapolated from the results obtained in proton and light ion induced reactions. While the Drell-Yan production exhibits the normal expected behaviour, the yield of J/psi in Pb-Pb interactions is abnormally low, as it lies 9 standard deviations below the expected value. Moreover, the departure from the expected behaviour increases significantly from peripheral to central collisions. (C) 1997 Elsevier Science B.V
Transverse momentum distributions of , Drell-Yan and continuum dimuons produced in Pb-Pb interactions at the SPS
NA50Muon pairs produced in Pb-Pb interactions at 158~GeV/ per nucleon are used to study the transverse momentum distributions of the \jpsi, \psip\ and dimuons in the mass continuum. In particular, the dependence of these distributions on the centrality of the Pb-Pb collision is investigated in detail
Transverse momentum distributions of J/, , Drell-Yan and continuum dimuons produced in Pb-Pb interactions at the SPS
Muon pairs produced in Pb-Pb interactions at 158~GeV/ per nucleon are used to study the transverse momentum distributions of the J/, and dimuons in the mass continuum. In particular, the dependence of these distributions on the centrality of the Pb-Pb collision is investigated in detail
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