166,635 research outputs found
Review of SIS Experimental Results on Strangeness
>A review of meson emission in heavy ion collisions at incident energies
around 1 -- 2 GeV is presented. It is shown how the shape of the
spectra and the various particle yields vary with system size, with centrality
and with incident energy. A statistical model assuming thermal and chemical
equilibrium and exact strangeness conservation (i.e. strangeness conservation
per collision) explains most of the observed features.
Emphasis is put onto the study of and emission. In the framework
of this statistical model it is shown that the experimentally observed equality
of and rates at threshold corrected energies is due to a crossing of two excitation functions. Furthermore,
the independence of the to ratio on the number of participating
nucleons observed between 1 and 10 GeV is consistent with this model.
The observed flow effects are beyond the scope of this model.Comment: 10 pages, 9 figures, Strangeness 2000, V International Conference on
Strangeness in Quark Matter, July, 2000, Berkeley, Californi
Survey of experimental data
>A review of meson emission in heavy ion collisions at incident energies from
SIS up to collider energies is presented. A statistical model assuming chemical
equilibrium and local strangeness conservation (i.e. strangeness conservation
per collision) explains most of the observed features.
Emphasis is put onto the study of and emission at low incident
energies. In the framework of this statistical model it is shown that the
experimentally observed equality of and rates at
``threshold-corrected'' energies is due to a
crossing of two excitation functions. Furthermore, the independence of the
ratio on the number of participating nucleons observed between SIS
and RHIC is consistent with this model.
It is demonstrated that the production at SIS energies occurs
predominantly via strangeness exchange and that this channel is approaching
chemical equilibrium. The observed maximum in the excitation
function is also seen in the ratio of strange to non-strange particle
production. The appearance of this maximum around 30 GeV is due to the
energy dependence of the chemical freeze-out parameters and .Comment: 13 pages, 14 figures, SQM2001 in Frankfurt, Sept. 2001, submitted to
IO
Strange Particle Production from SIS to LHC
>1A review of meson emission in heavy ion collisions at incident energies
from SIS up to collider energies is presented. A statistical model assuming
chemical equilibrium and local strangeness conservation (i.e. strangeness
conservation per collision) explains most of the observed features.
Emphasis is put onto the study of and emission at low incident
energies. In the framework of this statistical model it is shown that the
experimentally observed equality of and rates at
``threshold-corrected'' energies is due to a
crossing of two excitation functions. Furthermore, the independence of the
to ratio on the number of participating nucleons observed between
SIS and RHIC is consistent with this model.
It is demonstrated that the production at SIS energies occurs
predominantly via strangeness exchange and this channel is approaching chemical
equilibrium. The observed maximum in the excitation function is
also seen in the ratio of strange to non-strange particle production. The
appearance of this maximum around 30 GeV is due to the energy
dependence of the chemical freeze-out parameters and .Comment: Presented at the International Workshop "On the Physics of the
Quark-Gluon Plasma", Palaiseau, France, September 2001. 10 pages, 8 figure
Nonparametric estimation of extremal dependence
There is an increasing interest to understand the dependence structure of a
random vector not only in the center of its distribution but also in the tails.
Extreme-value theory tackles the problem of modelling the joint tail of a
multivariate distribution by modelling the marginal distributions and the
dependence structure separately. For estimating dependence at high levels, the
stable tail dependence function and the spectral measure are particularly
convenient. These objects also lie at the basis of nonparametric techniques for
modelling the dependence among extremes in the max-domain of attraction
setting. In case of asymptotic independence, this setting is inadequate, and
more refined tail dependence coefficients exist, serving, among others, to
discriminate between asymptotic dependence and independence. Throughout, the
methods are illustrated on financial data.Comment: 22 pages, 9 figure
Exchangeable Variable Models
A sequence of random variables is exchangeable if its joint distribution is
invariant under variable permutations. We introduce exchangeable variable
models (EVMs) as a novel class of probabilistic models whose basic building
blocks are partially exchangeable sequences, a generalization of exchangeable
sequences. We prove that a family of tractable EVMs is optimal under zero-one
loss for a large class of functions, including parity and threshold functions,
and strictly subsumes existing tractable independence-based model families.
Extensive experiments show that EVMs outperform state of the art classifiers
such as SVMs and probabilistic models which are solely based on independence
assumptions.Comment: ICML 201
Quotient correlation: A sample based alternative to Pearson's correlation
The quotient correlation is defined here as an alternative to Pearson's
correlation that is more intuitive and flexible in cases where the tail
behavior of data is important. It measures nonlinear dependence where the
regular correlation coefficient is generally not applicable. One of its most
useful features is a test statistic that has high power when testing nonlinear
dependence in cases where the Fisher's -transformation test may fail to
reach a right conclusion. Unlike most asymptotic test statistics, which are
either normal or , this test statistic has a limiting gamma
distribution (henceforth, the gamma test statistic). More than the common
usages of correlation, the quotient correlation can easily and intuitively be
adjusted to values at tails. This adjustment generates two new concepts--the
tail quotient correlation and the tail independence test statistics, which are
also gamma statistics. Due to the fact that there is no analogue of the
correlation coefficient in extreme value theory, and there does not exist an
efficient tail independence test statistic, these two new concepts may open up
a new field of study. In addition, an alternative to Spearman's rank
correlation, a rank based quotient correlation, is also defined. The advantages
of using these new concepts are illustrated with simulated data and a real data
analysis of internet traffic.Comment: Published in at http://dx.doi.org/10.1214/009053607000000866 the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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