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Shape of the $f_0(980)$ in $γγ\toπ^+π^-$

N. N. Achasov·G. N. Shestakov
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Abstract

The Belle Collaboration results on the observation of the $f_0(980)$ resonance in the reaction $γγ\toπ^+π^-$ are analyzed. It is argued that they point to the presence of mechanisms which give rise to a strong distortion of the $f_0(980)$ resonance shape in comparison with the shape of a solitary Breit-Wigner resonance. It is shown that the main factors responsible for the formation of the specific, steplike, shape of the $f_0(980)$ resonance in the $γγ\toπ^+π^-$ reaction cross section are the $K^+K^-$ loop mechanism of the $f_0(980)$ coupling to the $γγ$ system and the destructive interference between the background and $f_0(980)$ resonance contributions in the $π^+π^-$ invariant mass region below the $K^+K^-$ threshold.

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N. N. Achasov, G. N. Shestakov. 2005-07-25. Shape of the $f_0(980)$ in $γγ\toπ^+π^-$. https://doi.org/10.1103/physrevd.72.013006

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