Low energy parameters of the KK and ππ scalar - isoscalar interactions

Low energy parameters of the KK and ππ scalar-isoscalar interactions Abstract Threshold expansions of the ππ and KK spin 0 and isospin 0 scattering amplitudes are performed. Scattering lengths, effective ranges and so–called volume parameters are evaluated. Good agreement with the existing experimental data for the ππ scalar–isoscalar amplitude is found. An importance of future accurate measurements of the KK threshold parameters is stressed. New data are needed to understand the basic features of the scalar mesons. Kaon–antikaon interactions are very poorly known. A characteristic feature of the KK interactions is a presence of the annihilation processes in which a creation of the ππ pairs plays a very important role. Thus the KK and ππ channels are coupled together and should be treated simultaneously. Our knowledge of the meson–meson interactions is based mainly on the reactions in which the kaon or pion pairs are produced. The production processes of the scalar mesons f 0 (975) and a 0 (980) (which both decay into the KK pairs) have been studied in many experiments [1, 2] and new experiments like those at COSY (Jülich) [3], DAΦNE (Frascati) [4, 5] and CEBAF (Newport News) are planned. Unfortunately the existing KK and ππ data are not sufficiently precise to construct a unique model explaining 1