687 research outputs found
Nonperturbative and perturbative aspects of photo- and electroproduction of vector mesons
We discuss various aspects of vector meson production, first analysing the
interplay between perturbative and nonperturbative aspects of the QCD
calculation. Using a general method adapted to incorporate both perturbative
and nonpertubative aspects, we show that nonperturbative effects are important
for all experimentally available values of the photon virtuality Q2. We compare
the huge amount of experimental information now available with our theoretical
results obtained using a specific nonperturbative model without free
parameters, showing that quite simple features are able to explain the data.Comment: 19 page
Nonperturbative \gamma^* p Interaction in the Diffractive Regime
One of the challenging aspects of electroproduction at high-energy is the
understanding of the transition from real photons to virtual photons in the
GeV^2 region. We study inclusive electroproduction on the proton at small x_B
using a nonperturbative dipole-proton cross section calculated from the gauge
invariant gluon field correlators as input. By quark-hadron duality, we
construct a photon light cone wave function which links the ``hadronic''
behavior at small Q^2 to the ``perturbative'' behavior at large Q^2. It
contains quark masses which implement the transition from constituent quarks at
low Q^2 to current quarks at high Q^2. Our calculation gives a good description
of the structure function at fixed energy for Q^2<=10 GeV^2. Indications for a
chiral transition may already have been seen in the photon-proton cross
section.Comment: 28 pages, LaTeX, eps
Tracking Performance of the Scintillating Fiber Detector in the K2K Experiment
The K2K long-baseline neutrino oscillation experiment uses a Scintillating
Fiber Detector (SciFi) to reconstruct charged particles produced in neutrino
interactions in the near detector. We describe the track reconstruction
algorithm and the performance of the SciFi after three years of operation.Comment: 24pages,18 figures, and 1 table. Preprint submitted to NI
Nonlinear atom optics and bright gap soliton generation in finite optical lattices
We theoretically investigate the transmission dynamics of coherent matter
wave pulses across finite optical lattices in both the linear and the nonlinear
regimes. The shape and the intensity of the transmitted pulse are found to
strongly depend on the parameters of the incident pulse, in particular its
velocity and density: a clear physical picture for the main features observed
in the numerical simulations is given in terms of the atomic band dispersion in
the periodic potential of the optical lattice. Signatures of nonlinear effects
due the atom-atom interaction are discussed in detail, such as atom optical
limiting and atom optical bistability. For positive scattering lengths, matter
waves propagating close to the top of the valence band are shown to be subject
to modulational instability. A new scheme for the experimental generation of
narrow bright gap solitons from a wide Bose-Einstein condensate is proposed:
the modulational instability is seeded in a controlled way starting from the
strongly modulated density profile of a standing matter wave and the solitonic
nature of the generated pulses is checked from their shape and their
collisional properties
Hypogene Calcitization: Evaporite Diagenesis in the Western Delaware Basin
Evaporite calcitization within the Castile Formation of the Delaware Basin is more widespread and diverse than originally recognized. Coupled field and GIS studies have identified more than 1000 individual occurrences of calcitization within the Castile Formation outcrop area, which includes both calcitized masses (limestone buttes) and laterally extensive calcitized horizons (limestone sheets). Both limestone buttes and sheets commonly contain a central brecciated zone that we attribute to hypogene dissolution. Lithologic fabric of calcitized zones ranges from little alteration of original varved laminae to fabrics showing extensive laminae distortion as well as extensive vuggy and open cavernous porosity. Calcitization is most abundant in the western portion of the Castile outcrop region where surface denudation has been greatest. Calcitization often forms linear trends, indicating fluid migration along fractures, but also occurs as dense clusters indicating focused, ascending, hydrocarbon-rich fluids. Native sulfur, secondary tabular gypsum (i.e. selenite) and hypogene caves are commonly associated with clusters of calcitization. This assemblage suggests that calcium sulfate diagenesis within the Castile Formation is dominated by hypogene speleogemesis
Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
We review the most important experimental results from the first three years
of nucleus-nucleus collision studies at RHIC, with emphasis on results from the
STAR experiment, and we assess their interpretation and comparison to theory.
The theory-experiment comparison suggests that central Au+Au collisions at RHIC
produce dense, rapidly thermalizing matter characterized by: (1) initial energy
densities above the critical values predicted by lattice QCD for establishment
of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by
constituent interactions of very short mean free path, established most
probably at a stage preceding hadron formation; and (3) opacity to jets. Many
of the observations are consistent with models incorporating QGP formation in
the early collision stages, and have not found ready explanation in a hadronic
framework. However, the measurements themselves do not yet establish
unequivocal evidence for a transition to this new form of matter. The
theoretical treatment of the collision evolution, despite impressive successes,
invokes a suite of distinct models, degrees of freedom and assumptions of as
yet unknown quantitative consequence. We pose a set of important open
questions, and suggest additional measurements, at least some of which should
be addressed in order to establish a compelling basis to conclude definitively
that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.
HIV p24-Specific Helper T Cell Clones From Immunised Primates Recognize Highly Conserved Regions of HIV-l
We have investigated Th cell recognition of the
HIV core protein p24 by using CD4+ T cell clones
derived from cynomolgus macaques immunized
with hybrid HIV p24:Ty virus-like particles (VLP). T
cell lines from two immunized animals responded
to p24:Ty-VLP, control Ty-VLP, purified p24, and
whole inactivated HIV, indicating the presence of T
cells specific for p24 as well as the Ty carrier protein.
The HIV determinants recognized by the T cell
lines were identified by using a series of overlapping
peptides synthesized according to the sequence of
p24. Both T cell lines recognized peptide 11 (amino
acids 235-249) and peptide 14 (amino acids 265-
279). In addition, one T cell line also responded to
peptide 9 (amino acids 215-229). Definitive identification
of two T cell epitopes on p24 was confirmed
at the clonal level: from a total of four T cell clones
generated from one of the T cell lines, two respond
specifically to peptide 11 and two to peptide 14. The
T cell clones were CD4' and MHC class 11-restricted
and secreted IL-2 in response to stimulation with
purified p24, inactivated HIV or a single synthetic
peptide. The specificityof the Th clones for variant
peptides demonstrated cross-reactivity with two
simian immunodeficiency virus isolates, but only
limited responses to HIV-2 sequences. However, the
Th cell epitopes identified on p24 are highly conserved
between 12 HIV-1 isolates and were recognized
by both of the immunized primates. These
sequences may therefore be useful for priming a
broadly reactive immune response to HIV-1
Teor e composição do óleo essencial de quatro acessos e duas cultivares de manjericão (Ocimum basilicum L.)
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at GeV
We present first measurements of the evolution of the differential transverse
momentum correlation function, {\it C}, with collision centrality in Au+Au
interactions at GeV. {\it C} exhibits a strong dependence
on collision centrality that is qualitatively similar to that of number
correlations previously reported. We use the observed longitudinal broadening
of the near-side peak of {\it C} with increasing centrality to estimate the
ratio of the shear viscosity to entropy density, , of the matter formed
in central Au+Au interactions. We obtain an upper limit estimate of
that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.
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