2,305 research outputs found
Nucleon resonances and processes involving strange particles
An existing single resonance model with S11, P11 and P13 Breit-Wiegner
resonances in the s-channel has been re-applied to the old pi N --> K Lambda
data. It has been shown that the standard set of resonant parameters fails to
reproduce the shape of the differential cross section. The resonance parameter
determination has been repeated retaining the most recent knowledge about the
nucleon resonances. The extracted set of parameters has confirmed the need for
the strong contribution of a P11(1710) resonance. The need for any significant
contribution of the P13 resonance has been eliminated. Assuming that the Baker.
et al data set\cite{Bak78} is a most reliable one, the P11 resonance can not
but be quite narrow. It emerges as a good candidate for the non-strange counter
partner of the established pentaquark anti-decuplet.Comment: 5 pages, 2 figures, contribution to the NSTAR 2004 conference in
Grenobl
The importance of piN → K Lambda process for the pole structure of the P11 partial wave T-matrix in the coupled channel pion-nucleon partial wave analysis
The pole structure of the P11 pion-nucleon partial wave is examined with the
emphasis on the 1700 MeV energy domain. The mechanism of eliminating continuum
ambiguities in pion-nucleon partial wave analyses by using the coupled channel
formalism, presented elsewhere for the piN -> etaN channel, is applied for the
piN -> K Lambda channel, with the aim to clarify the issue whether physical
reality requires none (VPI/GWU), one (KH80, CMB, Kent, Pittsburgh/ANL,
Giessen), or possibly two (Zagreb) poles of the partial wave T-matrix in the
1700 MeV range. The role of second inelastic channel for resolving the dilemma
is demonstrated. It is pointed out that the experiments for the piN -> K Lambda
and piN -> K Sigma channel, extremely important for the 1700 MeV range, are old
and inconclusive so an urgent need for remeasuring that channel is stressed.Comment: 4 pages, 5 figures; talk held at NSTAR 2005 in Tallahassee, F
Numerical tripping of high-speed turbulent boundary layers
The influence of turbulence inflow generation on direct numerical simulations (DNS) of high-speed turbulent boundary layers at Mach numbers of 2 and 5.84 is investigated. Two main classes of inflow conditions are considered, based on the recycling/rescaling (RR) and the digital filtering (DF) approach, along with suitably modified versions. A series of DNS using very long streamwise domains is first carried out to provide reliable data for the subsequent investigation. A set of diagnostic parameters is then selected to verify achievement of an equilibrium state, and correlation laws for those quantities are obtained based on benchmark cases. Simulations using shorter domains, with extent comparable with that used in the current literature, are then carried out and compared with the benchmark data. Significant deviations from equilibrium conditions are found, to a different extent for the various flow properties, and depending on the inflow turbulence seeding. We find that the RR method yields superior performance in the evaluation of the inner-scaled wall pressure fluctuations and the turbulent shear stress. DF methods instead yield quicker adjustment and better accuracy in the prediction of wall friction and of the streamwise Reynolds stress in supersonic cases. Unrealistically high values of the wall pressure variance are obtained by the baseline DF method, while the proposed DF alternatives recover a closer agreement with respect to the benchmark. The hypersonic test case highlights that similar distribution of wall friction and heat transfer are obtained by both RR and DF baseline methods
Singularity structure of the pi N scattering amplitude in a meson-exchange model up to energies W < 2.0 GeV
Within the previously developed Dubna-Mainz-Taipei meson-exchange model, the
singularity structure of the pi N scattering amplitudes has been investigated.
For all partial waves up to F waves and c.m. energies up to W = 2 GeV, the
T-matrix poles have been calculated by three different techniques: analytic
continuation into the complex energy plane, speed-plot and the regularization
method. For all 4-star resonances, we find a perfect agreement between the
analytic continuation and the regularization method. We also find resonance
poles for resonances that are not so well established, but in these cases the
pole positions and residues obtained by analytic continuation can substantially
differ from the results predicted by the speed-plot and regularization methods.Comment: 21 pages, 4 figures, 4 table
Poles, the only true resonant-state signals, are extracted from a worldwide collection of partial wave amplitudes using only one, well controlled pole-extraction method
Each and every energy dependent partial-wave analysis is parameterizing the
pole positions in a procedure defined by the way how the continuous energy
dependence is implemented. These pole positions are, henceforth, inherently
model dependent. To reduce this model dependence, we use only one,
coupled-channel, unitary, fully analytic method based on the isobar
approximation to extract the pole positions from the each available member of
the worldwide collection of partial wave amplitudes which are understood as
nothing more but a good energy dependent representation of genuine experimental
numbers assembled in a form of partial-wave data. In that way, the model
dependence related to the different assumptions on the analytic form of the
partial-wave amplitudes is avoided, and the true confidence limit for the
existence of a particular resonant state, at least in one model, is
established. The way how the method works, and first results are demonstrated
for the S11 partial wave.Comment: 22 pages, 8 figures, 2 table
JKarma: A Highly-Modular Framework for Pattern-Based Change Detection on Evolving Data
Pattern-based change detection (PBCD) describes a class of change detection algorithms for evolving data. Contrary to conventional solutions, PBCD seeks changes exhibited by the patterns over time and therefore works on an abstract form of the data, which prevents the search for changes on the raw data. Moreover, PBCD provides arguments on the validity of the results because patterns mirror changes occurred with any form of evidence. However, the existing solutions differ on data representation, mining algorithm and change identification strategy, which we can deem as main modules of a general architecture, so that any PBCD task could be designed by accommodating custom implementations for those modules. This is what we propose in this paper through jKarma, a highly-modular framework for designing and performing PBCD
The detailed mechanism of the eta production in pp scattering up to the Tlab = 4.5 GeV
Contrary to very early beliefs, the experimental cross section data for the
eta production in proton-proton scattering are well described if pi and only
eta meson exchange diagrams are used to calculate the Born term. The inclusion
of initial and final state interactions is done in the factorization
approximation by using the inverse square of the Jost function. The two body
Jost functions are obtained from the S matrices in the low energy effective
range approximation. The danger of double counting in the p-eta final state
interaction is discussed. It is shown that higher partial waves in
meson-nucleon amplitudes do not contribute significantly bellow excess energy
of Q=100 MeV. Known difficulties of reducing the multi resonance model to a
single resonance one are illustrated.Comment: 10 pages, 5 figures, corrected typos in relation (3), changed content
(added section with differential cross sections
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