REACTIONS γγ→K+K− AND $\gamma \gamma \to K^0 \bar K^0 $ NEAR THRESHOLD

Abstract

The absence of the large Born term contribution found experimentally near the γγ→ K+K− reaction threshold is discussed. There are, at least, two reasons of the Born term suppression: i) the presence of a form factor and ii) the compensation of the Born term by the contributions from a0(980) and f0(975) resonances strongly coupled to the [Formula: see text] channel. This compensation is a natural consequence of the unitarity condition. In its turn, the isotopic invariance guarantees a cancellation of the a0(980) and f0(975) contributions in [Formula: see text]