IS THERE A NARROW-EPSILON UNDER THE RHO

The possibility that a narrow ε{lunate} resonance exists, approximately degenerate in mass and width with the ρ{variant}, is considered. It is shown that data on π+π- production near the ρ{variant} mass, including the full set of joint moments in π+p → π+π-Δ++ as well as the moments obtained with a polarized target in π-p → π-π+n, are consistent with the existence of such a resonance. Our method, which involves a compromise two-parameter fit to the mass dependence of some moments and the mass-averaged values of all moments, indicates that a broad ε{lunate} with a slowly varying phase shift and a rather low mass, 600 MeV, also fits the data. However, the two solutions could be distinguished by accurate measurements of the mass dependence of some moments, using existing data on π+p → π+π-Δ++, and the existence (or non-existence) of a narrow ε{lunate} clearly demonstrated. © 1979.