S. Ceci

Resolution of the multichannel anomaly in the extraction of S-matrix resonance-pole parameters

Inspired by anomalies which the standard scattering matrix pole-extraction procedures have produced in a mathematically well defined coupled-channel model, we have developed a new method based solely on the assumption of partial-wave analyticity. The new method is simple and applicable not only to theoretical predictions but to the empirical partial-wave data as well. Since the standard pole-extraction procedures turn out to be the lowest-order term of the proposed method the anomalies are understood and resolved.

The Re-Analysis of the 1700 MeV Structure of the P 11 Partial Wave Using the πN → KΛ Production Data

Abstract.We have used the Breit-Wigner resonance model with S11, P11, and P13 resonances in the s-channel to reanalyze the old πN → KΛ data with the aim to establish the origin of the prominent structure in the total cross section in the vicinity of 1700 MeV. We have found a new set of resonance parameters enforcing the experimentally observed structure of the total cross-section data simultaneously with the linear dependence of the differential cross sections with cos θ in the energy range 1650 MeV < W < 1800 MeV. Owing to the differential cross-section linearity, the P13 partial wave has been strongly attenuated in this model, and the total cross-section structure is attributed to the resonant behavior of the P11 partial wave. In this paper we show that, at least in the Breit-Wigner resonance model, it is not possible to achieve a detailed reproduction of the narrow 1700 MeV total cross-section peak using the standard partial widths. To understand the phenomenon, a much narrower width of a resonant state, the N(1710) P11 in our case, is required (Γ ≈ 68 MeV), but then the agreement of the model predictions with the total cross-section data at higher energies is lost. One way out is to allow for the existence of another P11 resonance in that energy range. The same feature is shown by the polarization data: The introduction of a much narrower resonance spoils the level of agreement which the Breit-Wigner resonance model is able to achieve with experiment, but the consistency is restored when another resonance is introduced. Analyzing the qqq or qqqq

The importance of η exchange in the pp→ppη process up to Tlab=4.5 GeV

\bar{q}

THE IMPORTANCE OF πN → KΛ PROCESS FOR THE POLE STRUCTURE OF THE P11 PARTIAL WAVE T-MATRIX IN THE COUPLED-CHANNEL PION-NUCLEON PARTIAL WAVE ANALYSIS

nature of the recommended narrow P11 structure in the neighborhood of 1700 MeV we reopen (remind of) the possibility that another P11 resonant state exists in addition to the standard N(1710) P11 PDG-resonance, and that one of the two states can be identified with the yet undiscovered cryptoexotic pentaquark state. To clarify the situation, we strongly recommend a remeasurement of the πN → KΛ process in the energy range 1650 MeV < W < 1800 MeV.

The importance of η exchange in the pp→ppη process up toTlab=4.5 GeV

The new and improved treatment of η-meson exchange diagrams turns out to be essential in order to fully describe both total cross-sections and, in particular, the challenging pp invariant mass distributions. Contrary to other approaches, the η-meson contribution in our model is comparable with the leading π-meson exchange term, and using the phenomenological final state interaction we have no need to include other mesons, like ρ and ω, in order to obtain good agreement with experiment.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.

Presence of extra P(11) resonances in Zagreb analysis since 1995

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.

The detailed mechanism of the eta production in pp scattering up to the Tlab = 4.5 GeV

The new and improved treatment of η-meson exchange diagrams turns out to be essential in order to fully describe both total cross-sections and, in particular, the challenging pp invariant mass distributions. Contrary to other approaches, the η-meson contribution in our model is comparable with the leading π-meson exchange term, and using the phenomenological final state interaction we have no need to include other mesons, like ρ and ω, in order to obtain good agreement with experiment.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.

Nucleon resonances and processes involving strange particles

The partial wave T-matrices for the pi N, eta N and pi2 N channels have been obtained within the framework of the coupled channel model using the pi N elastic and pi N --> eta N data base as input. It has been shown that for the P11 partial wave an equally good representation of the experimental data (namely the T(pi N,pi N) and T(pi N,eta N) T-matrices) can be obtained using either three, or four poles for the Green function propagator. However, the three Green function pole solution is not acceptable due to the structure of the extracted resonances. The two out of four P11 resonances, those lying in the energy range 1700 MeV < MR < 1800 MeV, are poorly determined, but they seem to be strongly inelastic. The inclusion of other inelastic channels is needed to determine masses and widths of missing resonances with greater precision.

The importance of eta exchange in the p p ---> p p eta process up to T(lab) = 4.5-GeV

The new and improved treatment of η-meson exchange diagrams turns out to be essential in order to fully describe both total cross-sections and, in particular, the challenging pp invariant mass distributions. Contrary to other approaches, the η-meson contribution in our model is comparable with the leading π-meson exchange term, and using the phenomenological final state interaction we have no need to include other mesons, like ρ and ω, in order to obtain good agreement with experiment.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.

Detailed analysis of eta production in proton-proton collisions

AbstractAn existing single resonance model with S11, P11 and P13 Breit-Wiegner resonances in the s-channel has been re-applied to the oldπN →KΛ data. It has been shown that the standard set of reso-nant parameters fails to reproduce the shape of the differential crosssection. The resonance parameter determination has been repeatedretaining the most recent knowledge about the nucleon resonances.The extracted set of parameters has confirmed the need for the strongcontribution of a P11(1710) resonance. The need for any significantcontribution of the P13 resonance has been eliminated. Assumingthat the Baker. et al data set[1] is a most reliable one, the P11 reso-nance can not but be quite narrow. It emerges as a good candidate forthe non-strange counter partner of the established pentaquark anti-decuplet. In spite of the fact that the experimental data for the process πN →KΛ,which show a distinct peeking around the energy range of 1700 MeV, areavailable for quite some time[1, 2] the existence of a P