448 research outputs found
Scaling Distributions of Quarks, Mesons and Proton for all , Energy and Centrality
We present the evidences for the existence of a universal scaling behavior of
the production of at all transverse momenta in heavy-ion collisions at
all centralities and all collision energies. The corresponding scaling behavior
of the quarks is then derived just before the quarks recombine with antiquarks
to form the pions. The degradation effect of the dense medium on the quark
is derived from the scaling distribution. In the recombination model it
is then possible to calculate the distributions of the produced proton
and kaon, which are scaling also. Experimentally verifiable predictions are
made. Implications of the existence of the scaling behavior are discussed.Comment: 10 pages in RevTeX, including 14 figures in eps file
Energy loss in high energy heavy ion collisions from the Hydro+Jet model
We investigate the effect of energy loss of jets in high energy heavy ion
collisions by using a full three-dimensional space-time evolution of a fluid
combined with (mini-)jets that are explicitly evolved in space-time. In order
to fit the pi^0 data for the Au+Au collisions at sqrt(s_{NN}) = 130 GeV, the
space-time averaged energy loss dE/dx(tau <= 3 fm/c) = 0.36 GeV/fm is extracted
within the model. It is found that most energy loss occurs at the very early
time less than 2 fm/c in the QGP phase and that energy loss in the mixed phase
is negligible within our parameterization for jet energy loss. This is a
consequence of strong expansion of the system.Comment: 4 pages, 5 figures; one figure adde
Reply to Comment of Gazdzicki and Heinz on Strangeness Enhancement in and
The Comment of Gazdzicki and Heinz is flawed because their assumed baryon
stopping power in is inconsistent with data and because they ignored half
the analysis based on the VENUS model. The Comment continues the misleading
presentation of strangeness enhancement by focusing on ratios of integrated
yields. Those ratios discard essential experimental information on the rapidity
dependence of produced and obscure discrepancies between different
data sets. Our conclusion remains that the NA35 minimum bias data on
indicate an anomalous enhancement of central
rapidity strangeness in few nucleon reactions that points to non-equilibrium
dynamics as responsible for strangeness enhancement in nuclear reactions.Comment: revtex file, 6 pages, submitted to Phys. Rev.
Dilepton from Disoriented Chiral Condensates
Disoriented chiral condensates are manifested as long wavelength pionic
oscillations and their interaction with the thermal environment can be a
significant source of dileptons. We calculate the yield of such dilepton
production within the linear sigma model and illustrate the basic features of
the dilepton spectrum in a schematic model. We find that the dilepton yield
with invariant mass near and below due to the soft pion modes can be
up to two orders of magnitude larger than the corresponding equilibrium yield.
We conclude with a discussion on how this enhancement can be detected by
present dilepton experiments.Comment: 15 pages, 9 figs, uses epsf and sprocl style files Contribution to
Proceedings, International Workshop on Astro Hadron Physics `Hadrons in Dense
Matter', APCTP, Seoul, Korea, October 199
Baryon Junction Stopping at the SPS and RHIC via HIJING/B
Baryon stopping at the SPS and RHIC energies is calculated by introducing a
new baryon junction mechanism into HIJING. The exchange of a baryon junction,
according to Regge phenomenology, leads to a cosh(y/2) rapidity dependence and
an s^(-1/4) energy dependence of the inclusive baryon cross section. This
baryon junction dynamics also leads naturally to enhanced p_T broadening in pA
and AA together with enhanced mid-rapidity hyperon production.Comment: Proceedings for Quark Matter 97; 4 pages, 1 eps-figur
Dependence of energy loss of jets on the initial thermodynamic state of deconfined matter at RHIC
The dependence of the radiative energy loss of fast partons on the initial
thermodynamic parameters is studied for deconfined matter to be expected at
RHIC. We demonstrate that the specific QCD radiation pattern with a quadratic
dependence of the energy loss on the propagated distance leads to a strong
increase of the energy loss with increasing initial entropy of deconfined
matter supposed its life-time is less than the average time to pass through the
medium. This is in contrast to a parameterization with constant energy loss per
unit length of propagation. For a sufficiently high initial temperature a
two-regime behavior of the energy loss as a function of the initial parton
momentum occurs. The angular structure of the energy loss of hard jets with
respect to the initial temperature is also discussed for RHIC conditions.Comment: 10 pages with fig
Specific Heat of Sr4Ru3O10
We have measured the specific heat of single crystals of the triple-layer
Ruddlesden-Popper material, Sr4Ru3O10, grown both in an image furnace and by
flux-growth. The flux grown sample has a sharp mean-field-like anomaly at the
onset of magnetic order, Tc = 102 K, but a much broader anomaly, indicative of
residual heterogeneity, is observed for the image furnace sample. Even for the
flux grown sample, however, the anomaly is at least an order of magnitude
smaller than one would expect for complete ordering of the spins. Neither
sample exhibits an anomaly at Tm ~ 50 K, where magnetic measurements suggest
that basal plane antiferromagnetism sets in. Anomalous behavior (e.g.
consistent with a term in the specific heat ~ T^3/2 as would be observed for a
three-dimensional ferromagnet with weak exchange) is observed at low
temperatures for both samples, indicative of the unusual magnetic order in this
material.Comment: 14 pages including 4 figure
The dihadron fragmentation function and its evolution
Dihadron fragmentation functions and their evolution are studied in the
process of annihilation. Under the collinear factorization
approximation and facilitated by the cut-vertex technique, the two hadron
inclusive cross section at leading order (LO) is shown to factorize into a
short distance parton cross section and a long distance dihadron fragmentation
function. We provide the definition of such a dihadron fragmentation function
in terms of parton matrix elements and derive its DGLAP evolution equation at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: 27 pages, 2 column, Revtex4, 21 figure
High-p_T pion and kaon production in relativistic nuclear collisions
High-p_T pion and kaon production is studied in relativistic proton-proton,
proton-nucleus, and nucleus-nucleus collisions in a wide energy range. Cross
sections are calculated based on perturbative QCD, augmented by a
phenomenological transverse momentum distribution of partons (``intrinsic
k_T''). An energy dependent width of the transverse momentum distribution is
extracted from pion and charged hadron production data in
proton-proton/proton-antiproton collisions. Effects of multiscattering and
shadowing in the strongly interacting medium are taken into account.
Enhancement of the transverse momentum width is introduced and parameterized to
explain the Cronin effect. In collisions between heavy nuclei, the model
over-predicts central pion production cross sections (more significantly at
higher energies), hinting at the presence of jet quenching. Predictions are
made for proton-nucleus and nucleus-nucleus collisions at RHIC energies.Comment: 26 pages in Latex, 19 EPS figure
Quenching of High pT Hadron Spectra by Hadronic Interactions in Heavy Ion Collisions at RHIC
Typically the materialization of high energetic transverse partons to
hadronic jets is assumed to occur outside the reaction zone in a relativistic
heavy ion collision. In contrast, a quantum mechanical estimate yields a time
on the order of only a few fm/c for building up the hadronic wavefunction for
jets with typical transverse momenta of pT < 10 GeV as accessible at RHIC
facilities. The role of possible elastic or inelastic collisions of these high
pT particles with the bulk of hadrons inside the fireball is addressed by means
of an opacity expansion in the number of collisions. This analysis shows that
the hadronic final state interactions can in principle account for the
modification of the (moderate) high pT spectrum observed for central collisions
at RHIC.Comment: 9 pages, 9 figures, standard revtex, final published versio
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