S-wave ππ scattering and the S∗ poles

Abstract

The I = 0 S-wave ππ scattering amplitude is analysed with a primary interest in the S ∗ . The amplitude corresponding to the S ∗ is parametrized in terms of pole positions. The recent CERN-Munich energy-independent partial-wave solution is reproduced better by an amplitude with two poles (on sheet II and sheet III) than by that with only one pole (on sheet II). The background phase is also analysed in detail and the long conjectured existence of the ϵ(700) is almost excluded.