885 research outputs found
Open Charm Enhancement in Pb+Pb Collisions at SPS
The statistical coalescence model for the production of open and hidden charm
is considered within the canonical ensemble formulation. The data for the
J/\psi multiplicity in Pb+Pb collisions at 158 A GeV are used for the model
prediction of the open charm yield. We find a strong enhancement of the open
charm production, by a factor of about 2--4, over the standard hard-collision
model extrapolation from nucleon-nucleon to nucleus-nucleus collisions. A
possible mechanism of the open charm enhancement in A+A collisions at the SPS
energies is proposed.Comment: 4 pages, Late
Open and Hidden Charm Production in Heavy Ion Collisions at Ultrarelativistic Energies
We consider the production of the open charm and J/psi mesons in heavy ion
collisions at BNL RHIC. We discuss several recently developed pictures for
J/psi production and argue that a measurement at RHIC energies is crucial for
disentangling these different descriptions.Comment: 19 pages, Latex, 5 PS-figures. v3: Fig.6 is adde
The High E_T Drop of J/psi to Drell-Yan Ratio from the Statistical c anti-c Coalescence Model
The dependence of the J/psi yield on the transverse energy E_T in heavy ion
collisions is considered within the statistical c anti-c coalescence model. The
model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the
high-E_T region (E_T > 100 GeV). Here E_T-fluctuations and E_T-losses in the
dimuon event sample naturally create the celebrated drop in the J/psi to
Drell-Yan ratio.Comment: 14 pages, REVTeX, 1 PS-figure. v2: References are corrected and
update
Elliptical flow -- a signature for early pressure in ultrarelativistic nucleus-nucleus collisions
Elliptical energy flow patterns in non-central Au(11.7AGeV) on Au reactions
have been studied employing the RQMD model. The strength of these azimuthal
asymmetries is calculated comparing the results in two different modes of RQMD
(mean field and cascade). It is found that the elliptical flow which is readily
observable with current experimental detectors may help to distinguish
different reasonable expansion scenarios for baryon-dense matter. The final
asymmetries are very sensitive to the pressure at maximum compression, because
they involve a partial cancelation between early squeeze-out and subsequent
flow in the reaction plane. This cancelation can be expected to occur in a
broad energy region covered by the current heavy ion fixed-target programs at
BNL and at CERN.Comment: 14 pages LaTeX including 3 postscript figure
Direct observation of homogeneous cavitation in nanopores
We report on the evaporation of hexane from porous alumina and silicon
membranes. These membranes contain billions of independent nanopores tailored
to an ink-bottle shape, where a cavity several tens of nanometers in diameter
is separated from the bulk vapor by a constriction. For alumina membranes with
narrow enough constrictions, we demonstrate that cavity evaporation proceeds by
cavitation. Measurements of the pressure dependence of the cavitation rate
follow the predictions of the bulk, homogeneous, classical nucleation theory,
definitively establishing the relevance of homogeneous cavitation as an
evaporation mechanism in mesoporous materials. Our results imply that porous
alumina membranes are a promising new system to study liquids in a deeply
metastable state.Comment: 14 pages , 4 figures. Source files also contain Supplemental Material
(Doebele_HomogeneousCavitationMembranes_SM.pdf
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Design of single spoke resonantors for Project X
Project X is based on a 3 GeV CW superconducting linac and is currently in the R&D phase awaiting CD-0 approval. The low-energy section of the Project X H{sup -} linac includes three types of super-conducting single spoke cavities operating at 325 MHz. SSR0 (18 cavities), SSR1 (20 cavities) and SSR2 (44 cavities) have a geometrical beta of {beta} = 0.11, 0.21 and 0.4 respectively. Single spoke cavities were selected for the linac in virtue of their higher r/Q values compared to standard Half Wave Resonator. Quarter Wave Resonators were not considered for such a high frequency. In this paper we present the decisions and analyses that lead to the final design of SSR0. Electro-magnetic and mechanical finite element analyses were performed with the purpose of optimizing the electro-magnetic design, minimizing frequency shifts due to helium bath pressure fluctuations and providing a pressure rating for the resonators that allow their use in the cryomodules
Photon Rates for Heavy-Ion Collisions from Hidden Local Symmetry
We study photon production from the hidden local symmetry approach that
includes pions, rho and a1 mesons and compute the corresponding photon emission
rates from a hadronic gas in thermal equilibrium. Together with experimental
radiative decay widths of the background, these rates are used in a
relativistic transport model to calculate single photon spectra in heavy-ion
collisions at SPS energies. We then employ this effective theory to test three
scenarios for the chiral phase transition in high-temperature nuclear matter
including decreasing vector meson masses. Although all calculations respect the
upper bound set by the WA80 Collaboration, we find the scenarios could be
distinguished with more detailed data.Comment: 12 pages, 12 Postscript figures; discussion of thermal equilibrium
rates expanded, minor corrections to text and graph
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
Charged particle production in the Pb+Pb system at 158 GeV/c per nucleon
Charged particle multiplicities from high multiplicity central interactions
of 158 GeV/nucleon Pb ions with Pb target nuclei have been measured in the
central and far forward projectile spectator regions using emulsion chambers.
Multiplicities are significantly lower than predicted by Monte Carlo
simulations. We examine the shape of the pseudorapidity distribution and its
dependence on centrality in detail.Comment: 17 pages text plus 12 figures in postscript 12/23/99 -- Add TeX
version of sourc
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