Quark structure of f0(980) from the radiative decays phi(1020)->gamma f0(980), gamma eta, gamma eta', gamma pi0 and f0(980)->gamma gamma

Abstract

Partial widths of the radiative decays $\varphi (1020)\to \gamma f_0(980)$, $\gamma \eta$, $\gamma {\eta }^{\prime }$, $\gamma {\pi }^0$ and $f_0(980)\to \gamma \gamma$ are calculated assuming all mesons under consideration to be $q\bar{q}$ states: $\varphi (1020)$ is dominantly an $s\bar{s}$ state ($n\bar{n}$ component $\lesssim 1$), $\eta$, ${\eta }^{\prime }$ and ${\pi }^0$ are standard $q\bar{q}$ states, $\eta =n\bar{n}\cos \theta -s\bar{s}\sin \theta$ and ${\eta }^{\prime }=n\bar{n}\sin \theta +s\bar{s}\cos \theta$ with $\theta \simeq 37^{\circ }$, and $f_0(980)$ is the $q\bar{q}$ meson with the flavour wave function $n\bar{n}\cos \varphi +s\bar{s}\sin \varphi$. Calculated partial widths for the decays $\varphi \to \gamma \eta$, $\gamma {\eta }^{\prime }$, $\gamma {\pi }^0$ are in a reasonable agreement with experiment. The measured value of the branching ratio $BR(\varphi \to \gamma f_0(980))$ requires $25^{\circ }\le |\varphi |\le 90^{\circ }$; for the decay $f_0(980)\to \gamma \gamma$ the agreement with data is reached at either $77^{\circ }\le \varphi \le 93^{\circ }$ or $(-54^{\circ })\le \varphi \le (-38^{\circ })$. Simultaneous analysis of the decays $\varphi (1020)\to \gamma f_0(980)$ and $f_0(980)\to \gamma \gamma$ provides arguments in favour of the solution with negative mixing angle $\varphi =-48^{\circ }\pm 6^{\circ }$.

some typos corrected, Fig 4. presented in more suitable form, some references are changed