Large isospin mixing in φ radiative decay and the spatial size of the f0(980)–a0(980) mesons

The measured rate for φ→γf0(980) appears to be larger than allowed on rather general grounds. We show that mixing between the f0(980) and a0(980), due to their dynamical interaction with the nearby KK̄ thresholds, radically affects some existing predictions of their production in φ radiative decay. We predict that Γ(φ→γf0)/Γ(φ→γa0)∼3; that ∑(b.r.(φ→γf0)+b.r.(φ→γa0))<5×10−4 with probable individual branching ratios ∼2×10−4 and 0.7×10−4, respectively.