g-parity 332.par.002002 Louis J. Sheehan,Eesquire

. Feynmnn diagrams for ψ production and (a) direct decay to hadrons, (b) second-order electromagnetic decay to hadrons. and (c) second-order electromagnetic decay to μ+μ-.
In processes (b) and (c), hadrons and muon-pairs are produced by virtual photons in exactly the same way that they are produced at off-resonance energies. If the observed hadrons were produced only through second-order electromagnetic decay, then the hadron/muon-pair production ratio, R, would be the same on-resonance as off. This is decidedly not the case. Since R is much larger on-resonance than off, both ψ and y’ do have direct hadronic decays.
More branching fractions for specific hadronic channels have been measured for the ψ and y’ than for any other particles. Most of these are of interest only to the specialist, but a few have told us a good deal about the psi particles. Since the second-order electromagnetic decays also complicate these analyses, we must again make on- and off-resonance comparisons between muon-pair production and the production of specific hadronic final states. In Fig. 8 we show such a comparison plotted against the number of pions observed in the final state [10]. Even numbers of pions observed are consistent with what is
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expected from second-order electromagnetic decays, while the observed odd- pion decays are much enhanced. The ψ decays appear, from these data, to be governed by a certain selection rule (G-parity conservation) that is known to govern only the behavior of hadrons, thus indicating that the ψ itself is a hadron.
4.4. Search for Other Narrow Resonances
By operating the SPEAR storage ring in a “scanning” mode, we have been able to carry out a systematic search for any other very narrow, psi-like resonances that may exist. In this scanning mode, the ring is filled and set to the initial energy for the scan; data are taken for a minute or two; the ring energy is increased by about an MeV; data are taken again; and so forth. Figure 9 shows these scan data from c.m. energies of about 3.2 to 8 GeV [11, 12]. No statistically significant peaks (other than the gf that was found in our first scan) were observed in this search, but this needs two qualifications. The first is that the sensitivity of the search extends down to a limit on possible resonances that have a cross section x width of about 5% to 10%, of that of the ψ. The second qualification is that the particular method of search is sensitive only to extremely narrow resonances like the ψ and y’; other, much broader resonances have been found at SPEAR, and we shall soon see how these apparently much different states fit into the picture.