T=0,J=0Pion-Pion Interaction

Abstract

A recent analysis of the process ${\pi }^{-}p\to {\pi }^{+}{\pi }^{-}n$ at energies close to threshold suggests that the $T=J=0\mathrm{}$ pion-pion phase shift ${{\delta }_0}^0$ may have a turnover behavior, starting off as a negative phase shift (with scattering length ∼-1.7 ${\mathrm{\mu }}^{-1\mathrm{}}$) but soon turning over and becoming positive. In this paper the $\pi N$ partial-wave "discrepancy" analysis is examined to find whether it is consistent with this kind of phase shift. The ABC effect is discussed briefly, and some possible consequences of a Castillejo-Dalitz-Dyson pole are suggested.