1,441 research outputs found
Production of Strange Clusters and Strange Matter in Nucleus-Nucleus Collisions at the AGS
Production probabilities for strange clusters and strange matter in Au+Au
collisions at AGS energy are obtained in the thermal fireball model. The only
parameters of the model, the baryon chemical potential and temperature, were
determined from a description of the rather complete set of hadron yields from
Si+nucleus collisions at the AGS. For the production of light nuclear fragments
and strange clusters the results are similar to recent coalescence model
calculations. Strange matter production with baryon number larger than 10 is
predicted to be much smaller than any current experimental sensitivities.Comment: 9 Pages (no figures
Hyperon-nucleon scattering and hyperon masses in the nuclear medium
We analyze low-energy hyperon-nucleon scattering using an effective field
theory in next-to-leading order. By fitting experimental cross sections for
laboratory hyperon momenta below 200 MeV/c and using information from the
hypertriton we determine twelve contact-interaction coefficients. Based on
these we discuss the low-density expansion of hyperon mass shifts in the
nuclear medium.Comment: 10 pages, 2 figure
Neutron Star Constraints on the H Dibaryon
We study the influence of a possible H dibaryon condensate on the equation of
state and the overall properties of neutron stars whose population otherwise
contains nucleons and hyperons. In particular, we are interested in the
question of whether neutron stars and their masses can be used to say anything
about the existence and properties of the H dibaryon. We find that the equation
of state is softened by the appearance of a dibaryon condensate and can result
in a mass plateau for neutron stars. If the limiting neutron star mass is about
that of the Hulse-Taylor pulsar a condensate of H dibaryons of vacuum mass 2.2
GeV and a moderately attractive potential in the medium could not be ruled out.
On the other hand, if the medium potential were even moderately repulsive, the
H, would not likely exist in neutron stars. If neutron stars of about 1.6 solar
mass were known to exist, attractive medium effects for the H could be ruled
out. Certain ranges of dibaryon mass and potential can be excluded by the mass
of the Hulse-Taylor pulsar which we illustrate graphically.Comment: Revised by the addition of a figure showing the region of dibaryon
mass and potential excluded by the Hulse-Taylor pulsar. 18 pages, 11 figures,
latex (submitted to Phys. Rev. C
Modeling Cluster Production at the AGS
Deuteron coalescence, during relativistic nucleus-nucleus collisions, is
carried out in a model incorporating a minimal quantal treatment of the
formation of the cluster from its individual nucleons by evaluating the overlap
of intial cascading nucleon wave packets with the final deuteron wave function.
In one approach the nucleon and deuteron center of mass wave packet sizes are
estimated dynamically for each coalescing pair using its past light-cone
history in the underlying cascade, a procedure which yields a parameter free
determination of the cluster yield. A modified version employing a global
estimate of the deuteron formation probability, is identical to a general
implementation of the Wigner function formalism but can differ from the most
frequent realisation of the latter. Comparison is made both with the extensive
existing E802 data for Si+Au at 14.6 GeV/c and with the Wigner formalism. A
globally consistent picture of the Si+Au measurements is achieved. In light of
the deuteron's evident fragility, information obtained from this analysis may
be useful in establishing freeze-out volumes and help in heralding the presence
of high-density phenomena in a baryon-rich environment.Comment: 31 pages REVTeX, 19 figures (4 oversized included as JPEG). For full
postscript figures (LARGE): contact [email protected]
Loosely bound hyperons in the SU(3) Skyrme model
Hyperon pairs bound in deuteron like states are obtained within the SU(3)
Skyrme model in agreement with general expectations from boson exchange models.
The central binding from the flavor symmetry breaking terms increases with the
strangeness contents of the interacting baryons whereas the kinetic non-linear
-model term fixes the spin and isospin of the bound pair. We give a
complete account of the interactions of octet baryons within the product
approximation to baryon number configurations.Comment: 35 pages REVTEX including 2 figs, with 3 further figs available on
request from [email protected] or from [email protected]
SI-94-TP3S2; STPHY-Th/94-
The Lambda-Lambda Interaction and ^{6}_{Lambda Lambda}He
An OBE potential model for the ^{1}S_0 S = -2 interaction is analyzed with
emphasis on the role of coupling between the Lambda Lambda, N Xi, and Sigma
Sigma channels. Singlet scalar exchange, an approximation to two-pion exchange,
is significant in all channels; surprisingly, the one-pion exchange component
is almost negligible. The size of the channel coupling as a function of the
overall strength of the OBE model potential is examined. Implications of the
analysis for the binding energy of ^{6}_{Lambda Lambda}He are considered; the
new experimental datum may suggest a consistency between the extracted Lambda
Lambda matrix element and the relation implied by SU(3) among OBE baryon-baryon
interactions. \\Comment: 4 pages brief report to Physical Review
Selective Photothermolysis of Cutaneous Pigmentation by Q-switched Nd: YAG Laser Pulses at 1064, 532. and 355nm
Exposure of skin to nanosecond-domain laser pulses affects the pigmentary system by a process called selective photothermolysis, in which melanosomes and pigmented cells are preferentially altered. Due to the broad absorption spectrum of melanin, this effect may occur with wavelengths that penetrate to vastly different depths within tissue, potentially producing different biologic responses. The effects of single near-ultraviolet (355nm), visible (532nm), and near infrared (1064nm) pulses of 10–12nsec duration were determined in guinea pig skin using gross, histologic, and electron microscopic observations. Threshold response in pigmented skin was a transient immediate ash-white discoloration, requiring 0.11, 0.20 and 1.0J/cm2, at 355, 532, and 1064 nm, respectively. At each wavelength, melanosomes were reputed within keratinocytes and melanocytes, with cytoplasmic and nuclear alterations. Delayed epidermal depigmentation occurred, followed by gradual repigmentation. Deep follicular cells were altered only at 532 and 1064 nm, which produced permanent leukotrichia. The action spectrum for threshold response was consistent with mechanisms implied by selective photothermolysis. These data may be useful for consideration of treatment for cutaneous pigmentation abnormalities or unwanted follicular pigmentation, or both
Chiral Dynamics of Low-Energy Kaon-Baryon Interactions with Explicit Resonance
The processes involving low energy and interactions (where
or ) are studied in the framework of heavy baryon chiral
perturbation theory with the (1405) resonance appearing as an
independent field.
The leading and next-to-leading terms in the chiral expansion are taken into
account. We show that an approach which explicitly includes the (1405)
resonance as an elementary quantum field gives reasonable descriptions of both
the threshold branching ratios and the energy dependence of total cross
sections.Comment: 16 pages, 6 figure
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