801 research outputs found

### Testing the Space-Time Structure of Event Generators

We report on work done in collaboration with Klaus Kinder-Geiger and John
Ellis which aims at connecting the space-time structure of event generator
simulations with observable output.Comment: 16 pages LaTeX, including 5 postscript figures. To appear in the
Proceedings of ``RHIC Physics and Beyond - Kay Kay Gee Day'' (Brookhaven
National Laboratory, 23 Oct 1998), ed. by B. Muller and R.D. Pisarski, AIP
Conference Proceeding

### Massless particles, electromagnetism, and Rieffel induction

The connection between space-time covariant representations (obtained by
inducing from the Lorentz group) and irreducible unitary representations
(induced from Wigner's little group) of the Poincar\'{e} group is re-examined
in the massless case. In the situation relevant to physics, it is found that
these are related by Marsden-Weinstein reduction with respect to a gauge group.
An analogous phenomenon is observed for classical massless relativistic
particles. This symplectic reduction procedure can be (`second') quantized
using a generalization of the Rieffel induction technique in operator algebra
theory, which is carried through in detail for electro- magnetism. Starting
from the so-called Fermi representation of the field algebra generated by the
free abelian gauge field, we construct a new (`rigged') sesquilinear form on
the representation space, which is positive semi-definite, and given in terms
of a Gaussian weak distribution (promeasure) on the gauge group (taken to be a
Hilbert Lie group). This eventually constructs the algebra of observables of
quantum electro- magnetism (directly in its vacuum representation) as a
representation of the so-called algebra of weak observables induced by the
trivial representation of the gauge group.Comment: LaTeX, 52 page

### Bose-Einstein Final State Symmetrization for Event Generators of Heavy Ion Collisions

We discuss algorithms which allow to calculate identical two-particle
correlations from numerical simulations of relativistic heavy ion collisions. A
toy model is used to illustrate their properties.Comment: Talk given at CRIS'98 (Catania, June 8-12, 1998), to appear in
"CRIS'98: Measuring the size of things in the Universe: HBT interferometry
and heavy ion physics", (S. Costa et al., eds.), World Scientific, Singapore,
1998. (10 pages Latex, 1 eps-figure, extended version of conference
proceedings, Fig1 a,b added and corresponding discussion enlarged

### Bose-Einstein Correlations in a Space-Time Approach to e+ e- Annihilation into Hadrons

A new treatment of Bose-Einstein correlations is incorporated in a space-time
parton-shower model for e+ e- annihilation into hadrons. Two alternative
afterburners are discussed, and we use a simple calculable model to demonstrate
that they reproduce successfully the size of the hadron emission region. One of
the afterburners is used to calculate two-pion correlations in e+ e- -> Z^0 ->
hadrons and e+ e- -> W+ W- -> hadrons. Results are shown with and without
resonance decays, for correlations along and transverse to the thrust jet axis
in these two classes of events.Comment: 30 pages, Latex, 8 figure

### Medium-induced color flow softens hadronization

Medium-induced parton energy loss, resulting from gluon exchanges between the
QCD matter and partonic projectiles, is expected to underly the strong
suppression of jets and high-$p_T$ hadron spectra observed in
ultra-relativistic heavy ion collisions. Here, we present the first
color-differential calculation of parton energy loss. We find that color
exchange between medium and projectile enhances the invariant mass of energetic
color singlet clusters in the parton shower by a parametrically large factor
proportional to the square root of the projectile energy. This effect is seen
in more than half of the most energetic color-singlet fragments of
medium-modified parton branchings. Applying a standard cluster hadronization
model, we find that it leads to a characteristic additional softening of
hadronic spectra. A fair description of the nuclear modification factor
measured at the LHC may then be obtained for relatively low momentum transfers
from the medium

### Yano-Koonin-Podgoretskii Parametrisation of the Hanbury Brown-Twiss Correlator

The Yano-Koonin-Podgoretskii (YKP) parametrisation of Hanbury Brown-Twiss
(HBT) two-particle correlation functions opens new strategies for extracting
the emission duration and testing the longitudinal expansion in heavy-ion
collisions. Based on the recently derived model-independent expressions, we
present a detailed parameter study of the YKP parameters for a finite,
hydrodynamically expanding source model of heavy-ion collisions. For the class
of models studied here, we show that the three YKP radius parameters have an
interpretation as longitudinal extension, transverse extension and emission
duration of the source in the YKP frame. This frame is specified by the fourth
fit parameter, the Yano-Koonin velocity which describes to a good approximation
the velocity of the fluid element with highest emissivity and allows to test
for the longitudinal expansion of the source. Deviations from this
interpretation of the YKP parameters are discussed quantitatively.Comment: 38 pages, REVTeX, 11 PS-figures, to be published in Z.Phys.

### Space-time Characteristics of the Fireball from HBT Interferometry

We present the Yano-Koonin-Podgoretskii parametrisation of the correlation
function. Compared to the conventionally used Cartesian parametrisation, this
one provides more straightforward measurement of the duration of the emission
process in the fireball and a clearer signal of the longitudinal expansion,
which is expected in ulrarelativistic heavy ion collisions.Comment: 13 pages LaTeX,3 figures incl. with epsf-style. Proceedings of "Heavy
Ion Workshop on Particle Physics", Sept. 2.-6., 1996, Bratislava, Slovakia,
misprint in Eq.(27) correcte

### Medium Modification of the Jet Properties

In the case that a dense medium is created in a heavy ions collision,
high-E_t jets are expected to be broadened by medium-modified gluon emission.
This broadening is directly related, through geometry, to the energy loss
measured in inclusive high-p_t particle suppression. We present here the
modifications of jet observables due to the presence of a medium for the case
of azimuthal jet energy distributions and k_t-differential multiplicities
inside the jets.Comment: 4 pages, 3 postscript figures. Proceedings for Quark Matter 200

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