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P. Lipa

Publications and source records attributed to P. Lipa.

13 recordsLinked to original sources
arXiv2007

HBT shape analysis with q-cumulants

Taking up and extending earlier suggestions, we show how two- and threedimensional shapes of second-order HBT correlations can be described in a multivariate Edgeworth expansion around gaussian ellipsoids, with expansion coefficients, identified as the cumulants of pair momentum difference q, acting as shape parameters. Off-diagonal terms dominate both the character and magnitude of shapes. Cumulants can be measured directly and so the shape analysis has no need for fitting.

nucl-th↗
arXiv1998

Fix-point Multiplier Distributions in Discrete Turbulent Cascade Models

One-point time-series measurements limit the observation of three-dimensional fully developed turbulence to one dimension. For one-dimensional models, like multiplicative branching processes, this implies that the energy flux from large to small scales is not conserved locally. This then renders the random weights used in the cascade curdling to be different from the multipliers obtained from a backward averaging procedure. The resulting multiplier distributions become solutions of a fix-point problem. With a further restoration of homogeneity, all observed correlations between multipliers in the energy dissipation field can be understood in terms of simple scale-invariant multiplicative branching processes.

chao-dyn↗
arXiv1998

Multiplicity Dependence of Like-Sign and Opposite-Sign Correlations in $\bar{p}p$ Reactions

Discussions about Bose-Einstein correlations between decay products of coproduced W-bosons again raise the question about the behaviour of correlations if several strings are produced. This is studied by the multiplicity dependence of correlation functions of particle pairs with like-sign and opposite-sign charge in $\bar{p}p$ reactions at $\sqrt{s} = 630$ GeV.

hep-ex↗
arXiv1997

Probing Hierarchical Clustering by Scale-Scale Correlations of Wavelet Coefficients

It is of fundamental importance to determine if and how hierarchical clustering is involved in large-scale structure formation of the universe. Hierarchical evolution is characterized by rules which specify how dark matter halos are formed by the merging of halos at smaller scales. We show that scale-scale correlations of the matter density field are direct and sensitive measures to quantify this merging tree. Such correlations are most conveniently determined from discrete wavelet transforms. Analyzing two samples of Ly-alpha forests of QSO's absorption spectra, we find significant scale-scale correlations whose dependence is typical for a branching process. Therefore, models which predict a "history" independent evolution are ruled out and the halos hosting the Ly-alpha clouds must have gone through a "history" dependent merging process during their formation.

astro-ph↗
arXiv1997

A sensitive test for models of Bose-Einstein correlations

Accurate and sensitive measurements of higher order cumulants open up new approaches to pion interferometry. It is now possible to test whether a given theoretical prediction can consistently match cumulants of both second and third order. Our consistency test utilizes a new technique combining theoretically predicted functions with experimentally determined weights in a quasi-Monte Carlo approach. Testing a general quantum statistics-based framework of Bose-Einstein correlations with this technique, we find that predictions for third order cumulants differ significantly from UA1 data. This discrepancy may point the way to more detailed dynamical information.

hep-ph↗
arXiv1996

Pion interferometry with higher-order cumulants

We have measured second- and third-order cumulants in UA1 data ($\bar pp$ collisions at 630 GeV/c). Rather than quoting numerical values for source parameters, we have used these in three checks to test the ``quantum statistics'' theory for consistency over these cumulants. In the process, we have found a method for folding theoretical correlation functions with experimental one-particle distributions. Our preliminary results appear to indicate that, for the specific tests performed, the data contradicts the theory.

hep-ph↗
arXiv1996

Generalized moments and cumulants for samples of fixed multiplicity

Factorial moments and cumulants are usually defined with respect to the unconditioned Poisson process. Conditioning a sample by selecting events of a given overall multiplicity $N$ necessarily introduces correlations. By means of Edgeworth expansions, we derive generalized cumulants which define correlations with respect to an arbitrary process rather than just the Poisson case. The results are applied to correlation measurements at fixed $N$, to redefining short-range vs.\ long-range correlations and to normalization issues.

hep-ph↗
arXiv1994

Unbiased Estimators for Correlation Measurements

Higher order correlation measurements involve multiple event averages which must run over unequal events to avoid statistical bias. We derive correction formulas for small event samples, where the bias is largest, and utilize the results to achieve savings in CPU time consumption for the star integral. Results from a simple model of correlations illustrate the utility and importance of these corrections. Single-event correlation measurements such as in galaxy distributions and envisaged at RHIC must take great care to avoid this unnecessary pitfall.

hep-ex↗
arXiv1993

Star Integrals and Unbiased Estimators

We review in brief the development and implementation of the Star integral, a tool yielding measurements of correlations much superior to conventional methods. A version for use in pion interferometry is explained. We also show how effects of non-poissonian overall multiplicity distributions may be eliminated if desired and quote results eliminating statistical biases arising in correlation measurements within small samples.

hep-ph↗
arXiv1993

Integral correlation measures for multiparticle physics

We report on a considerable improvement in the technique of measuring multiparticle correlations via integrals over correlation functions. A modification of measures used in the characterization of chaotic dynamical sytems permits fast and flexible calculation of factorial moments and cumulants as well as their differential versions. Higher order correlation integral measurements even of large multiplicity events such as encountered in heavy ion collisons are now feasible. The change from ``ordinary'' to ``factorial'' powers may have important consequences in other fields such as the study of galaxy correlations and Bose-Einstein interferometry.

hep-ph↗