Home OALib Journal OALib PrePrints Submit Ranking News My Lib FAQ About Us Follow Us+
 Title Keywords Abstract Author All
Search Results: 1 - 10 of 100 matches for " "
 Physics , 1997, Abstract: A three-channel, multi-resonance, unitary model developed in 1995 is used to determine the $\pi N \rightarrow \eta N$ and $\eta N \rightarrow \eta N$ amplitudes using as input the latest data for the dominant $S_{11}$ $\pi N$ elastic scattering partial wave following suggestions of Prof. G. H\"{o}hler. The sign error in the numerical evaluation of the dispersion integral in the original publication is eliminated. The remaining weighted data set for the $\pi N \rightarrow \eta N$ total and differential cross sections is used as in the original publication. The correction of the numerical error influences the $\eta N$ cusp effect and improves the quality of the fit to the input data. However, our new result for the $\eta N$ scattering length, $a_{\eta N }= (0.717 \pm 0.030) + i (0.263 \pm 0.025)$ fm, is a sole consequence of the correction of the $S_{11}$ input and suggests that the $\eta d$ system is unbound or loosely bound.
 Physics , 2008, DOI: 10.1103/PhysRevC.80.015207 Abstract: Within a chiral constituent quark model approach, $\eta$-meson production on the proton {\it via} electromagnetic and hadron probes are studied. With few parameters, differential cross-section and polarized beam asymmetry for \gamma p \to \eta p$and differential cross section for$\pi^- p\to \eta n$processes are calculated and successfully compared with the data in the center-of-mass energy range from threshold up to 2 GeV. The five known resonances$S_{11}(1535)$,$S_{11}(1650)$,$P_{13}(1720)$,$D_{13}(1520)$, and$F_{15}(1680)$are found to be dominant in the reaction mechanisms in both channels. Possible roles plaied by new resonances are also investigated and in the photoproduction channel, significant contribution from$S_{11}$- and$D_{15}$-resonances, with masses around 1715 MeV and 2090 MeV, respectively, are deduced. For the so-called missing resonances, no evidence is found within the investigated reactions. The helicity amplitudes and decay widths of$N^* \to \pi N, \eta N$are also presented, and found consistent with the PDG values.  Physics , 1999, DOI: 10.1103/PhysRevC.60.035208 Abstract: The coupled pi+N, eta+N, gamma+N systems are described by a K-matrix method. The parameters in this model are adjusted to get an optimal fit to pi+N -> pi+N, pi+N -> eta+N, gamma+N -> pi+N and gamma+N -> eta+N data in an energy range of about 100 MeV each side of the eta-threshold. The coupling of photons to the N(1535) state is extracted and also an alternative to the current S11(gamma+N -> pi+N) amplitudes suggested. Expansions are given for the eta-eta and gamma-eta amplitudes in terms of the eta-momentum. Effects of interference of this state with background potential interactions are discussed and experimental consequences are indicated.  M. Svec Physics , 1996, DOI: 10.1103/PhysRevD.55.4355 Abstract: The measurements of reactions$\pi^- p \to \pi^- \pi^+ n$and$\pi^+ n \to \pi^+ \pi^- p$on polarized targets at CERN found a strong dependence of pion production amplitudes on nucleon spin. Analyses of recent measurements of$\pi^- p \to \pi^0\pi^0 n$reaction on unpolarized targets by GAMS Collaboration at 38 GeV/c and BNL E852 Collaboration at 18 GeV/c use the assumption that pion production amplitudes do not depend on nucleon spin, in conflict with the CERN results on polarized targets. We show that measurements of$\pi^- p \to \pi^0\pi^0 n$and$\pi^- p \to \eta\eta n$on unpolarized targets can be analysed in a model independent way in terms of 4 partial-wave intensities and 3 independent interference phases in the mass region where$S$- and$D$-wave dominate. We also describe model-independent amplitude analysis of$\pi^- p \to \pi^0\pi^0 n$reaction measured on polarized target, both in the absence and in the presence of$G$-wave amplitudes. We suggest that high statistics measurements of reactions$\pi^- p \to \pi^0 \pi^0 n$and$\pi^- p \to \eta\eta n\$ be made on polarized targets at Protvino IHEP and at BNL, and that model-independent amplitude analyses of this polarized data be performed to advance hadron spectroscopy on the level of spin dependent production amplitudes.