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

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

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