4,145 research outputs found
Strange Hadron Resonances: Freeze-Out Probes in Heavy-Ion Collisions
Hyperon resonances are becoming an extremely useful tool allowing the study
of the properties of hadronic fireballs made in heavy ion collisions. Their
yield, compared to stable particles with the same quark composition, depends on
hadronization conditions. The resonance's short lifetime makes them ideal
probes of the fireball chemical freeze-out mechanisms. An analysis of resonance
abundance in heavy ion collisions should be capable of distinguishing between
possible hadronization scenarios, in particular between sudden and gradual
hadronization. In this paper, we review the existing SPS and RHIC experimental
data on resonance production in heavy ion collisions, and discuss in terms of
both thermal and microscopic models the yields of the two observed resonances,
K* and Lambda(1520). We show how freeze-out properties, namely chemical
freeze-out temperature and the lifetime of the interacting hadron phase which
follows, can be related to resonance yields. Finally, we apply these methods to
SPS and RHIC measurements, discuss the significance and interpretations of our
findings, and suggest further measurements which may help in clarifying
existing ambiguities.Comment: To appear in the proceedings of Pan American Advanced Studies
Institute on New States of Matter in Hadronic Interactions (PASI 2002),
Campos do Jordao, Brazil, 7-18 Jan 2002; American Institute of Physics 2002.
v2: reference and language correctio
Lambda(1520) production in d+Au collisions at RHIC
Recent results of (1520) resonance production in d+Au collisions at
200 GeV are presented and discussed in terms of the
evolution and freeze-out conditions of a hot and dense fireball medium. Yields
and spectra are compared to results from p+p and Au+Au collisions. The
(1520)/ ratio in d+Au collisions ratio is consistent with the
ratio in p+p collisions. This suggests a short time for elastic interactions
between chemical and thermal freeze-out. One can conclude that the interaction
volume in d+Au collisions is small.Comment: 4 Pages, 3 figures, conference proceedings Quark Matter 200
Recurrent cerebellar architecture solves the motor-error problem
Current views of cerebellar function have been heavily influenced by the models of Marr and Albus, who suggested that the climbing fibre input to the cerebellum acts as a teaching signal for motor learning. It is commonly assumed that this teaching signal must be motor error (the difference between actual and correct motor command), but this approach requires complex neural structures to estimate unobservable motor error from its observed sensory consequences.
We have proposed elsewhere a recurrent decorrelation control architecture in which Marr-Albus models learn without requiring motor error. Here, we prove convergence for this architecture and demonstrate important advantages for the modular control of systems with multiple degrees of freedom. These results are illustrated by modelling adaptive plant compensation for the three-dimensional vestibular ocular reflex. This provides a functional role for recurrent cerebellar connectivity, which may be a generic anatomical feature of projections between regions of cerebral and cerebellar cortex
Resonance production from jet fragmentation
Short lived resonances are sensitive to the medium properties in heavy-ion
collisions. Heavy hadrons have larger probability to be produced within the
quark gluon plasma phase due to their short formation times. Therefore heavy
mass resonances are more likely to be affected by the medium, and the
identification of early produced resonances from jet fragmentation might be a
viable option to study chirality. The high momentum resonances on the away-side
of a triggered di-jet are likely to be the most modified by the partonic or
early hadronic medium. We will discuss first results of triggered
hadron-resonance correlations in Cu+Cu heavy ion collisions.Comment: Hot Quarks Colorado 2008 Proceedings, 4 pages 5 figure
Resonance production in heavy ion collisions
Recent results of resonance production from RHIC at
200 GeV and SPS at 17 GeV are presented and discussed in
terms of the evolution and freeze-out conditions of a hot and dense fireball
medium. Yields and spectra are compared with thermal model predictions at
chemical freeze-out. Deviations in the low transverse momentum region of the
resonance spectrum of the hadronic decay channel, suggest a strongly
interaction hadronic phase between chemical and kinetic freeze-out. Microscopic
models including resonance rescattering and regeneration are able to describe
the trend of the data. The magnitude of the regeneration cross sections for
different inverse decay channels are discussed. Model calculations which
include elastic hadronic interactions between chemical freeze-out and thermal
freeze-out based on the K(892)/K and (1520)/ ratios suggest a
time between two freeze-outs surfaces of 4 fm/c. The difference
in momentum distributions and yields for the (1020) resonance
reconstructed from the leptonic and hadronic decay channels at SPS energy are
discussed taking into account the impact of a hadronic phase and possible
medium modifications.Comment: 8 pages, 4 figures, conference proceedings (SQM2004
What do we learn from Resonance Production in Heavy Ion Collisions?
Resonances with their short life time and strong coupling to the dense and
hot medium are suggested as a signature of the early stage of the fireball
created in a heavy ion collision \cite{rap00,lut01,lut02}. The comparison of
resonances with different lifetimes and quark contents may give information
about time evolution and density and temperature of during the expanding of
fireball medium. Resonances in elementary reactions have been measured since
1960. Resonance production in elementary collisions compared with heavy ion
collisions where we expect to create a hot and dense medium may show the direct
of influence of the medium on the resonances. This paper shows a selection of
the recent resonance measurements from SPS and RHIC heavy ion colliders.Comment: 10 pages, 8 figures, HotQuarks 2004 conference proceeding
Effect of Hydrostatic Pressure on the Superconductivity in NaxCoO2.yH2O
The effect of hydrostatic pressure on the superconducting transition
temperature of Na{0.35}CoO{2}.yH{2}O was investigated by ac susceptibility
measurements up to 1.6 GPa. The pressure coefficient of T{c} is negative and
the dependence T{c}(p) is nonlinear over the pressure range investigated. The
magnitude of the average dlnT{c}/dp=-0.07 GPa^{-1} is comparable to the
pressure coefficient of electron-doped high-T{c} copper oxide superconductors
with a similar value of T{c}. Our results provide support to the assumption of
two-dimensional superconductivity in Na{0.35}CoO{2}.yH{2}O, which is similar to
the cuprate systems, and suggest that intercalation of larger molecules may
lead to an enhancement of T{c}.Comment: Revised Manuscrip
Statistical hadronization phenomenology in fluctuations at ultra-relativistic energies
We discuss the information that can be obtained from an analysis of
fluctuations in heavy ion collisions within the context of the statistical
model of particle production. We then examine the recently published
experimental data on ratio fluctuations, and use it to obtain constraints on
the statistical properties (physically relevant ensemble, degree of chemical
equilibration, scaling across energies and system sizes) and freeze-out
dynamics (amount of reinteraction between chemical and thermal freeze-out) of
the system.Comment: Proceedings, SQM2009. Fig. 4, the main results figure, was wrong due
to editing mistake, now correcte
- …