20 research outputs found
A QCD space-time analysis of quarkonium formation and evolution in hadronic collisions
The production of heavy quarkonium as QQbar bound-states in hadron-hadron
collisions is considered within the framework of a space-time description,
combining parton-cascade evolution with a coalescence model for bound-state
formation. The `hard' production of the initial QQbar, directly or via gluon
fragmentation and including both color-singlet and color-octet contributions,
is calculated from the PQCD cross-sections. The subsequent development of the
QQbar system is described within a space-time generalization of the DGLAP
parton-evolution formalism in position- and momentum-space. The actual
formation of the bound-states is accomplished through overlap of the QQbar pair
and a spectrum of quarkonium wave-functions. This coalescence can only occur
after sufficent gluon radiation reduces the QQbar relative velocity to a value
commensurate with the non-relativistic kinematics of these bound systems. The
presence of gluon participants in the cascade then is both necessary and leads
to the natural inclusion of both color-singlet and color-octet mechanisms. The
application of this approach to pp (ppbar) collisions from sqrt(s)= 30 GeV - 14
TeV reveals very decent agreement with available data from ISR and Tevatron -
without the necessity of introducing fit parameters. Moreover, production
probabilities are calculated for a complete spectrum of charmonium and
bottonium states, with the relative significance compared to open charm
(bottom) production. An analysis of the space-time development is carried
through which sheds light on the relevance of gluon radiation and
color-structure, suggesting a correponding experimental investigation.Comment: 37 pages including 16 postscript figure
Hadronization in Z0 decay
The confinement transition from the quark and gluon degrees of freedom
appropriate in perturbation theory to the hadrons observed by real world
experiments is poorly understood. In this strongly interacting transition
regime we presently rely on models, which to varying degrees reflect possible
scenarios for the QCD dynamics. Because of the absence of beam and target
remnants, and the clean experimental conditions and high event rates, e+e-
annihilation to hadrons at the Z0 provides a unique laboratory, both
experimentally and theoretically, for the study of parton hadronization. This
review discusses current theoretical understanding of the hadronization of
partons, with particular emphasis on models of the non-perturbative phase, as
implemented in Monte Carlo simulation programs. Experimental results at LEP and
SLC are summarised and considered in the light of the models. Suggestions are
given for further measurements which could help to produce more progress in
understanding hadronization.Comment: Topical review, to appear in J.Phys.G, 80 page
Global analysis of three traveling vortex events during the November 1993 storm using the assimilative mapping of ionospheric electrodynamics technique
Global analysis of 3 travelling vortex events during the November 1993 storm, using the assimilative mapping of ionospheric electrodynamics technique
Evolution Effects in ... Fragmentation into Charmonium
In Z 0 decay into prompt charmonium, i.e. charmonium not originating from B-meson decays, the most important contribution is expected to come from colour-octet mechanisms. However, previous fixed-order calculations of the colour-octet contribution contain large logarithms which, in a more complete treatment, should be resummed to all orders. We study this resummation by using a Monte Carlo QCD cascade model and find that the fixed-order colour-octet result is diminished by 15%. We compare the Monte Carlo calculations with results obtained by using analytical evolution equations. 1 Introduction The production of charmonium and bottomonium states in various processes, especially at high-energy colliders [1], has recently received considerable experimental and theoretical interest. New data have become available from p¯p [2], ep [3] and e + e \Gamma [4--6] colliders. Theoretically, it has been realized that quarkonium production at colliders is dominated by parton fragmentation ..