High-statistics measurement of neutral-pion pair production in two-photon collisions

We present a high-statistics measurement of differential cross sections and the total cross section for the process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ in the kinematic range $0.6\text{ }\text{ }\mathrm{GeV}\ensuremath{\le}W\ensuremath{\le}4.0\text{ }\text{ }\mathrm{GeV}$ and $|\mathrm{cos}{\ensuremath{\theta}}^{*}|\ensuremath{\le}0.8$, where $W$ and ${\ensuremath{\theta}}^{*}$ are the energy and pion scattering angle, respectively, in the $\ensuremath{\gamma}\ensuremath{\gamma}$ center-of-mass system. Differential cross sections are fitted to obtain information on S, ${\mathrm{D}}_{0}$, ${\mathrm{D}}_{2}$, ${\mathrm{G}}_{0}$, and ${\mathrm{G}}_{2}$ waves. The G waves are important above $W\ensuremath{\simeq}1.6\text{ }\text{ }\mathrm{GeV}$. The general behavior of partial waves is studied by fitting differential cross sections in a simple parametrization where amplitudes contain resonant contributions and smooth background. The ${\mathrm{D}}_{2}$ wave is dominated by the ${f}_{2}(1270)$ meson whose parameters are consistent with the current world averages. The ${\mathrm{D}}_{0}$ wave contains a ${f}_{2}(1270)$ component, whose fraction is fitted. For the S wave, the ${f}_{0}(980)$ parameters are found to be consistent with the values determined from our recent ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ data. In addition to the ${f}_{0}(980)$, the S wave prefers to have another resonance-like contribution whose parameters are obtained.