How to See the Chiral Structure of QCD Vacuum in Low Energy $\pi -\pi$ Scattering

Abstract

Precise measurement of the $\pi \pi$-phase shift ${\delta }_0^0(E)$ at very low energies would provide, for the first time, the experimental evidence in favour of or against the existence of a large quark condensate in the QCD vacuum, which is standardly postulated as the mechanism of the spontaneous breakdown of chiral symmetry in QCD. The contribution of Da$\varphi$ne to this discovery could be decisive.

Comments: Invited talk at the Worshop on Physics and detectors at DAFNE, April 1995. 13 pages, 1 Figure: Postscript file appended at the end