The K + -nucleon elastic scattering process has been reexamined in light of recent measurements which have found a narrow exotic S=+1 resonance in their KN invariant mass distributions. We have analyzed the existing database in order to consider the effect of a narrow state on fits to K + -nucleon observables.PACS numbers: 13.75. Jz, 11.80.Et, 14.20.Jn An analysis of isoscalar and isovector contributions to K + -nucleon scattering, using K + p and K + d data, was published [1] by the VPI group in 1992. The interest in this reaction was driven by a search for possible Z * resonances. At the time of the VPI analysis, only isovector pole parameters had been reported in the Review of Particle Properties [2] (RPP). Breit-Wigner parameters were available for two isoscalar states. By including K + d elastic scattering and breakup data, an improved study of the isoscalar component was performed. Both isovector and isoscalar poles were reported. However, the inferred widths were of the order of 100 MeV, and could be "explained" as pseudoresonances whose resonance-like behavior was induced by the opening of channels such as K + ∆ and K * N . As a result, these states were removed from the RPP with the statement that "the general prejudice against baryons not made of three quarks and the lack of any experimental activity" precluded any foreseeable progress.Recent measurements [3,4,5,6] from SPring-8, ITEP, Jefferson Lab, and ELSA have dramatically changed the status of Z * resonances (now denoted as Θ states). Unlike, the broad resonancelike structures seen in previous K + N analyses, these groups have reported very narrow peaks in their KN mass distributions. The reported masses have been consistent, clustered around 1540 MeV, with widths less than 25 MeV. These results are in remarkable agreement with a chiral soliton prediction of a Θ + state at 1530 MeV, with a width less than 15 MeV [7]. In order to understand how this state could have eluded previous studies of K + N scattering data, we have reanalyzed this reaction, focusing on the 1540 MeV region. While there are suggestions that this state should be seen in the P 01 partial wave, we have scanned for S-, P-, and D-wave (S 01 , S 11 , P 01 , P 03 , P 11 , P 13 , D 03 , D 05 , D 13 , and D 15 ) structures as well. Width estimates have generally been given as upper limits. For this reason, we have allowed for much lower values. As there have been essentially no new data for this reaction since our last published fit, we have used the 1992 result as a starting point. The fitting strategy and database are fully documented in Ref. [1]. Below, we give only our results from a search for narrow structures.Narrow resonances were added to the VPI analysis using a product S-matrix approach. The added state was assumed to be an elastic KN resonance with an energy-independent width. An additional background S-matrix was also included, S B = (1 + iK)/(1 − iK), with an underlying K-matrix proportional to phase space. Data were then analyzed with resonances covering a grid of ma...

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A proton-proton bremsstrahlung experiment has been carried out at TRIUMF using a 280-MeV polarized proton beam impinging on a liquid-hydrogen target. All three outgoing particles were detected: the higher-energy proton in a magnetic spectrometer, the lower-energy proton with plastic scintillators, and the photon in lead-glass Cherenkov detectors. The experiment shows the first unambiguous evidence for off-shell effects in the free nucleon-nucleon interaction, in that the analyzing powers disagree strongly with the predictions of the soft-photon approximation (which incorporates only on-shell information) but are consistent with the results of calculations using the Bonn and Paris potentials.

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