Pion-nucleon data in the momentum range 1.6 to lOGeV/c are analyzed.
As an inters mediate step in the analysis, an impact parameter model, which describes the data primarily in terms of diffractive and peripheral contributions, is used. Many of the resulting partial wave amplitudes show strong resonance-like behavior.
The masses. widths and elasticities of resonances with spins j = 7/2,.... 21/2 are estimated.
A great deal is known at the present time about the low-lying states (masses less than 2000 MeV) of the baryon spectrum. Much of this information has come from detailed analyses [l-3] of low-energy meson-baryon scattering, and these have been successful in determining the masses, spins, widths. etc. of the various resonances that are present. These results have been particularly important for testing quark models ]4] and in helping to elucidate some of the finer details of the effective quark interaction [ 5, 61.
However, all models of baryons predict that there should be a continued sequence of higher-lying excited states. It is natural therefore to ask where they are. This paper describes a search that was made in the pion-nucleon system to see whether indeed such higher states existed, and if they did, to try and obtain estimates of the resonance parameters.
In Section 2, we first give some illustrations from experimental data which suggest that there may indeed be resonances lying above the region that has been studied so far, that is for plab 2 2.7 GeV/c. With these encouraging hints, we next consider how to make a detailed study of the data. Here one is faced with two major problems. The first is that. above 2 GeV/c, the quality of the experimental data rapidly deteriorates. Unlike the situation at lower energies, differential cross sections have not been measured over the whole range of scattering angle, apart from a few well-separated energies. Polarization measurements, not too plentiful at lower energies, become extremely meager above 2 GeV/c. The luxuries of lower energies (accurate data at closely spaced energies) therefore do not exist. The second major problem involves the standard methods of analysis. These usually involve at some stage a parametrization of the individual complex partial wave amplitudes and a lengthy