7,447 research outputs found
Nuclear modification at sqrt{s_{NN}}=17.3 GeV, measured at NA49
Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity
in Pb+Pb reactions at sqrt{s_{NN}}=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-},
by the NA49 experiment. The nuclear modification factors R_{AA}, R_{AA/pA} and
R_{CP} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV.
The modification factor R_{AA} shows a rapid increase with transverse momentum
in the covered region. The modification factor R_{CP} shows saturation well
below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200
GeV RHIC results closely in the available transverse momentum range for all
particle species. For pi^{+/-} above 2.5 GeV/c transverse momentum, the
measured suppression is smaller than that observed at RHIC. The nuclear
modification factor R_{AA/pA} for pi^{+/-} stays well below unity.Comment: Proceedings of Quark Matter 2008 conferenc
Proton-Deuteron Elastic Scattering from 2.5 to 22.5 MeV
We present the results of a calculation of differential cross sections and
polarization observables for proton-deuteron elastic scattering, for proton
laboratory energies from 2.5 to 22.5 MeV. The Paris potential parametrisation
of the nuclear force is used. As solution method for the charged-composite
particle equations the 'screening and renormalisation approach' is adopted
which allows to correctly take into account the Coulomb repulsion between the
two protons. Comparison is made with the precise experimental data of Sagara et
al. [Phys. Rev. C 50, 576 (1994)] and of Sperison et al. [Nucl. Phys. A422, 81
(1984)].Comment: 24 pages, 8 eps figures, uses REVTe
Momentum Space Integral Equations for Three Charged Particles: Diagonal Kernels
It has been a long-standing question whether momentum space integral
equations of the Faddeev type are applicable to reactions of three charged
particles, in particular above the three-body threshold. For, the presence of
long-range Coulomb forces has been thought to give rise to such severe
singularities in their kernels that the latter may lack the compactness
property known to exist in the case of purely short-range interactions.
Employing the rigorously equivalent formulation in terms of an
effective-two-body theory we have proved in a preceding paper [Phys. Rev. C
{\bf 61}, 064006 (2000)] that, for all energies, the nondiagonal kernels
occurring in the integral equations which determine the transition amplitudes
for all binary collision processes, possess on and off the energy shell only
integrable singularities, provided all three particles have charges of the same
sign, i.e., all Coulomb interactions are repulsive. In the present paper we
prove that, for particles with charges of equal sign, the diagonal kernels, in
contrast, possess one, but only one, nonintegrable singularity. The latter can,
however, be isolated explicitly and dealt with in a well-defined manner. Taken
together these results imply that modified integral equations can be
formulated, with kernels that become compact after a few iterations. This
concludes the proof that standard solution methods can be used for the
calculation of all binary (i.e., (in-)elastic and rearrangement) amplitudes by
means of momentum space integral equations of the effective-two-body type.Comment: 36 pages, 2 figures, accepted for publication in Phys. Rev.
Are there S=-2 Pentaquarks?
Recent evidence for pentaquark baryons in the channels ,
and their anti-particles claimed by the NA49 collaboration is
critically confronted with the vast amount of existing data on
spectroscopy which was accumulated over the past decades. It is shown that the
claim is at least partially inconsistent with these data. In addition two
further exotic channels of the pentaquark type available in the NA49 data are
investigated. It is argued that this study leads to internal inconsistency with
the purported signals
Major scientific challenges and opportunities in understanding magnetic reconnection and related explosive phenomena throughout the universe
This is a group white paper of 100 authors (each with explicit permission via email) from 51 institutions on the topic of magnetic reconnection which is relevant to 6 thematic areas. Grand challenges and research opportunities are described in observations, numerical modeling and laboratory experiments in the upcoming decade.https://ui.adsabs.harvard.edu/abs/2019BAAS...51c...5J/abstractAccepted manuscrip
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Minimum Cell Connection in Line Segment Arrangements
We study the complexity of the following cell connection problems in segment arrangements. Given a set of straight-line segments in the plane and two points a and b in different cells of the induced arrangement:
[(i)] compute the minimum number of segments one needs to remove so that there is a path connecting a to b that does not intersect any of the remaining segments; [(ii)] compute the minimum number of segments one needs to remove so that the arrangement induced by the remaining segments has a single cell.
We show that problems (i) and (ii) are NP-hard and discuss some special, tractable cases. Most notably, we provide a near-linear-time algorithm for a variant of problem (i) where the path connecting a
to b must stay inside a given polygon P with a constant number of holes, the segments are contained in P, and the endpoints of the segments are on the boundary of P. The approach for this latter result uses homotopy of paths to group the segments into clusters with the property that either all segments in a cluster or none participate in an optimal solution
Long-range behavior of the optical potential for the elastic scattering of charged composite particles
The asymptotic behavior of the optical potential, describing elastic
scattering of a charged particle off a bound state of two charged, or
one charged and one neutral, particles at small momentum transfer
or equivalently at large intercluster distance
, is investigated within the framework of the exact three-body
theory. For the three-charged-particle Green function that occurs in the exact
expression for the optical potential, a recently derived expression, which is
appropriate for the asymptotic region under consideration, is used. We find
that for arbitrary values of the energy parameter the non-static part of the
optical potential behaves for as
. From this we derive for the
Fourier transform of its on-shell restriction for the behavior , i.e.,
dipole or quadrupole terms do not occur in the coordinate-space asymptotics.
This result corroborates the standard one, which is obtained by perturbative
methods. The general, energy-dependent expression for the dynamic
polarisability is derived; on the energy shell it reduces to the
conventional polarisability which is independent of the energy. We
emphasize that the present derivation is {\em non-perturbative}, i.e., it does
not make use of adiabatic or similar approximations, and is valid for energies
{\em below as well as above the three-body dissociation threshold}.Comment: 35 pages, no figures, revte
Three charged particles in the continuum. Astrophysical examples
We suggest a new adiabatic approach for description of three charged
particles in the continuum. This approach is based on the Coulomb-Fourier
transformation (CFT) of three body Hamiltonian, which allows to develop a
scheme, alternative to Born-Oppenheimer one.
The approach appears as an expansion of the kernels of corresponding integral
transformations in terms of small mass-ratio parameter. To be specific, the
results are presented for the system in the continuum. The wave function
of a such system is compared with that one which is used for estimation of the
rate for triple reaction which take place as a step of
-cycle in the center of the Sun. The problem of microscopic screening for
this particular reaction is discussed
New results from fluctuation analysis in NA49 at the CERN SPS
The exploration of the phase diagram of strongly interacting matter,
particularly the study of the phase transition from hadronic to partonic matter
and the search for a hypothetical critical endpoint of the first order
transition line, is one of the most challenging tasks in present heavy ion
physics.
In this talk new results on chemical (particle ratio), transverse momentum,
multiplicity and azimuthal angle fluctuations will be presented. We also
discuss their connection to the onset of deconfinement and to the critical
endpoint.Comment: The Proceedings of the International Conference "Critical Point and
Onset of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201
Investigations on alternative substances for control of apple scab - Results from Conidia germinating tests and experiments with plant extracts
The intention of this research project, which was supported within the "Bundesprogramm Ökologischer
Landbau", was to find alternatives for the control of Venturia inaequalis for the organic fruitgrower.
Beside the investigations on reducing the ascospore potential on fallen leaves, experiments
were conducted in laboratory, greenhouses and in orchard to test direct control of scab with different
plant extracts, concentrations and methods of extraction. Extracts from Inula viscosa, Quillaja
saponaria-bark, citrus-species (AGROMIL) and Saponaria officinalis revealed a distinct efficacy
against apple scab in greenhouse studies on apple seedlings. ELOT-VIS, CHITOPLANT, COMCAT,
MOOSEXTRAKT, SILIOPLANT und FZB 24 did not show sufficient efficacy with the application schedule
used for control of scab. Mixtures of Quillaja-saponine and sulphur reduced effectively apple scab
incidence. In an experiment concerning rain stability Citrus-extract and Quillaja-saponine showed a
lower efficacy against scab after a simulated rain of 5 mm. The screening of different supplements
to Citrus-extract as surfactants and adhesives revealed GREEMAX and BIOPLUSS as promising additives.
Both combinations showed an efficacy comparable to copperoxychloride corresponding to
400 g elementary copper per ha
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