48,542 research outputs found
Recombination of Shower Partons at High in Heavy-Ion Collisions
A formalism for hadron production at high \pt in heavy-ion collisions has
been developed such that all partons hadronize by recombination. The
fragmentation of a hard parton is accounted for by the recombination of shower
partons that it creates. Such shower partons can also recombine with the
thermal partons to form particles that dominate over all other possible modes
of hadronization in the GeV range. The results for the high \pt
spectra of pion, kaon, and proton agree well with experiments. Energy loss of
partons in the dense medium is taken into account on the average by an
effective parameter by fitting data, and is found to be universal independent
of the type of particles produced, as it should. Due to the recombination of
thermal and shower partons, the structure of jets produced in nuclear
collisions is different from that in collisions. The consequence on
same-side correlations is discussed.Comment: This revised version contains minor changes and a new figure
The Relic Abundance of Long-lived Heavy Colored Particles
Long-lived colored particles with masses m > 200 GeV are allowed by current
accelerator searches, and are predicted by a number of scenarios for physics
beyond the standard model. We argue that such "heavy partons'' effectively have
a geometrical cross section (of order 10 mb) for annihilation at temperatures
below the QCD deconfinement transition. The annihilation process involves the
formation of an intermediate bound state of two heavy partons with large
orbital angular momentum. The bound state subsequently decays by losing energy
and angular momentum to photon or pion emission, followed by annihilation of
the heavy partons. This decay occurs before nucleosynthesis for m < 10^{11} GeV
for electrically charged partons and m < TeV for electrically neutral partons.
This implies that heavy parton lifetimes as long as 10^{14} sec are allowed
even for heavy partons with m ~ TeV decaying to photons or hadrons with
significant branching fraction.Comment: 13 pages, 4 figures. Minor revision
Parton coalescence at RHIC
Using a covariant coalescence model, we study hadron production in
relativistic heavy ion collisions from both soft partons in the quark-gluon
plasma and hard partons in minijets. Including transverse flow of soft partons
and independent fragmentation of minijet partons, the model is able to describe
available experimental data on pion, kaon, and antiproton spectra. The
resulting antiproton to pion ratio is seen to increase at low transverse
momenta and reaches a value of about one at intermediate transverse momenta, as
observed in experimental data at RHIC. A similar dependence of the antikaon to
pion ratio on transverse momentum is obtained, but it reaches a smaller value
at intermediate transverse momenta. At high transverse momenta, the model
predicts that both the antiproton to pion and the antikaon to pion ratio
decrease and approach those given by the perturbative QCD. Both collective flow
effect and coalescence of minijet partons with partons in the quark-gluon
plasma affect significantly the spectra of hadrons with intermediate transverse
momenta. Elliptic flows of protons, Lambdas, and Omegas have also been
evaluated from partons with elliptic flows extracted from fitting measured pion
and kaon elliptic flows, and they are found to be consistent with available
experimental data.Comment: 12 pages, 11 figure
Pedestal and Peak Structure in Jet Correlation
We study the characteristics of correlation between particles in jets
produced in heavy-ion collisions. In the framework of parton recombination we
calculate the and distributions of a pion associated with a
trigger particle. The origin of the pedestal in is related to the
longitudinal expansion of the thermal partons that are enhanced by the energy
loss of hard partons traversing the bulk medium. The peaks in and
are related to the same angular spread of the shower partons in a
jet cone. No artificial short- or long-range correlations are put in by hand. A
large part of the correlation between hadrons in jets is due to the correlation
among the shower partons arising from momentum conservation. Recombination
between thermal and shower partons dominates the correlation characterisitics
in the intermediate region.Comment: 14 pages in LaTex and 2 figures in ep
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