1,462 research outputs found
J/psi dissociation by light mesons in an extended Nambu Jona-Lasinio model
An alternative model for the dissociation of the J/psi is proposed. Chiral
symmetry is properly implemented. Abnormal parity interactions and mesonic form
factors naturally arise from the underlying quark sub-structure. Analytic
confinement for the light quarks is generated by appropriately chosen the quark
interaction kernels. Dissociation cross sections of the J/psi by either a pion
or a rho meson are then evaluated and discussed.Comment: 24 pages, 13 figures, final versio
Higher excitations of and in dilepton spectra
We consider lepton pair production via two-hadron annihilation through
various isoscalar vector mesons within hot, baryon-free matter. This is
tantamount to constructing effective form factors which we model using a
vector-meson-dominance approach and compare with experiment. In particular, we
consider the reactions and + c.c. . We find that and are visible in the mass
spectrum for the thermal production rate above the
tail and even above the results---both of which were
considered important in their respective mass regions.Comment: RevTeX, 9 pages, 6 (uuencoded) figures; to appear in Phys. Rev
Computational study of LnGaO3 (Ln=La+Gd) perovskites
Atomistic simulation techniques have been used to study the thermal properties of perovskite-type LnGaO3 (Ln = La-Gd). A set of interatomic potentials describing interatomic interactions in these compounds was developed and tested over a wide temperature range through utilizing free energyminimization.The predicted dielectric constants, thermal expansion coefficients, phonon density of states and its projections, heat capacity and entropy, elastic moduli, Gruneisen parameters, surface energies for main crystallographic directionsand Debye temperatures are in good agreement with the limited available experimental data. Perovskite-type LnGaO3 (Ln = La-Gd) compounds have been examined under conditions to which substrate materials are typically subjected. Only a narrow region in the phase diagram of LnGaO3 (Ln = La-Gd) and their solid solutions is recommended for use in substrate applications
Agglutinated foraminifera from the Turonian–Coniacian boundary interval in Europe – paleoenvironmental remarks and stratigraphy
Agglutinated foraminiferal assemblages of the Turonian–Coniacian from the
GSSP (Global Boundary Stratotype Section and Point) of Salzgitter–Salder (Subhercynian Cretaceous Basin, Germany) and
other sections, including Bielefeld–Ostwestfalendamm (Münsterland Cretaceous
Basin, Germany) and the Dover–Langdon Stairs (Anglo-Paris Basin, England), from
the temperate European shelf realm were studied in order to collect
additional stratigraphic and paleoenvironmental information. Stable carbon
isotopes were measured for the Bielefeld–Ostwestfalendamm section to
establish a reliable stratigraphic correlation with other sections. Highly
diverse agglutinated foraminiferal assemblages were obtained from sections
in the German basins, whereas the fauna from Dover is less rich in taxa and
less abundant. In the German basinal sections, a morphogroup
analysis of agglutinated foraminifera and the calculated diversities imply
normal marine settings and oligotrophic to mesotrophic bottom-water
conditions. Furthermore, acmes of agglutinated foraminifera correlate
between different sections and can be used for paleoenvironmental analysis.
Three acmes of the species Ammolagena contorta are recorded for the Turonian–Coniacian
(perplexus to lower striatoconcentricus zones, lower scupini Zone, and hannovrensis Zone) and likely imply a shift to more
oligotrophic bottom-water conditions. In the upper scupini Zone below the
Turonian–Coniacian boundary, an acme of Bulbobaculites problematicus likely indicates enhanced nutrient
availability.
In general, agglutinated foraminiferal morphogroups display a gradual shift
from Turonian oligotrophic environments towards more mesotrophic conditions
in the latest Turonian and Coniacian.</p
Baryon flow at SIS energies
We calculate the baryon flow in the energy range from .25 to
in a relativistic transport model for and
collisions employing various models for the baryon self energies. We find that
to describe the flow data of the FOPI Collaboration the strength of the vector
potential has to be reduced at high relative momentum or at high density such
that the Schr\"odinger- equivalent potential at normal nuclear density
decreases above 1 GeV relative kinetic energy and approaches zero above 2 GeV.Comment: 20 pages, LATEX, 7 PostScript figure
Quark-Gluon Plasma at RHIC and the LHC: Perfect Fluid too Perfect?
Relativistic heavy ion collisions have reached energies that enable the
creation of a novel state of matter termed the quark-gluon plasma. Many
observables point to a picture of the medium as rapidly equilibrating and
expanding as a nearly inviscid fluid. In this article, we explore the evolution
of experimental flow observables as a function of collision energy and attempt
to reconcile the observed similarities across a broad energy regime in terms of
the initial conditions and viscous hydrodynamics. If the initial spatial
anisotropies are very similar for all collision energies from 39 GeV to 2.76
TeV, we find that viscous hydrodynamics might be consistent with the level of
agreement for v2 of unidentified hadrons as a function of pT . However, we
predict a strong collision energy dependence for the proton v2(pT). The results
presented in this paper highlight the need for more systematic studies and a
re-evaluation of previously stated sensitivities to the early time dynamics and
properties of the medium.Comment: 11 pages, 9 figures, submitted to the New Journal of Physics focus
issue "Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to
QCD Plasmas
Omega meson as a chronometer and thermometer in hot-dense hadronic matter
Changes in the properties of the vector mesons in hot and dense hadronic
matter, as produced in heavy ion collisions, lead to the intriguing possibility
of the opening of the decay channel \omega \ra \rho \pi, for the omega meson,
which is impossible in free space. This along with the channel \omega \pi \ra
\pi \pi would result in a decrease in its effective life-time enabling it to
decay within the hot zone and act as a chronometer in contradiction to the
commonly held opinion and would have implications vis a vis determination of
the size of the region through pion interferometry. A new peak and a radically
altered shape of the low invariant mass dilepton spectra appears due to
different shift in the masses of and mesons. The Walecka model
is used for the underlying calculation for the sake of illustration.Comment: To appear in Phys. ReV.
Efficient index handling of multidimensional periodic boundary conditions
An efficient method is described to handle mesh indexes in multidimensional
problems like numerical integration of partial differential equations, lattice
model simulations, and determination of atomic neighbor lists. By creating an
extended mesh, beyond the periodic unit cell, the stride in memory between
equivalent pairs of mesh points is independent of their position within the
cell. This allows to contract the mesh indexes of all dimensions into a single
index, avoiding modulo and other implicit index operations.Comment: 2 pages, 0 figure
Lepton pairs from thermal mesons
We study the net dielectron production rates from an ensemble of thermal
mesons, using an effective Lagrangian to model their interaction. The coupling
between the electromagnetic and the hadronic sectors is done through the vector
meson dominance approach. For the first time, a complete set of light mesons is
considered. We include contributions from decays of the type
V~(PS)~~PS~(V)~+~, where V is a vector meson and PS is a
pseudoscalar, as well as those from binary reactions PS~+~PS, V~+~V, and
V~+~PS~. Direct decays of the type V~
are included and shown to be important. We find that the dielectron invariant
mass spectrum naturally divides in distinct regions: in the low mass domain the
decays from vector and pseudoscalar mesons form the dominant contribution. The
pion--pion annihilation and direct decays then pick up and form the leading
signal in an invariant mass region that includes the complex
and extends up to the . Above invariant mass ~1~GeV other
two-body reactions take over as the prominent mechanisms for lepton pair
generation. These facts will have quantitative bearing on the eventual
identification of the quark--gluon plasma.Comment: In ReVTeX 3.0, 9 figs. available from above email address. McGill
93/8, TPI-MINN-93/19-
Photons from axial-vector radiative decay in a hadron gas
Strange and non-strange axial-vector meson radiative decays contribute to
photon production in hadron gas. One- and two-hadron radiative decay modes of
, and are studied. At 200 MeV
temperature and for a narrow range in photon energies they contribute more to
the net thermal photon production rate than ,
or . They provide
significant contribution to the rate for photon energies as high as 1.5--2.0
GeV. For higher energies they are less important.Comment: 10 pages + 7 figures uuencoded in separate file, MSUCL-92
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