# High-statistics study of neutral-pion pair production in two-photon collisions - High Energy Physics - Experiment

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Abstract: The differential cross sections for the process $\gamma \gamma \to \pi^0\pi^0$ have been measured in the kinematic range 0.6 GeV $< W < 4.1$ GeV,$|\cos \theta^*|<0.8$ in energy and pion scattering angle, respectively, in the$\gamma\gamma$ center-of-mass system. The results are based on a 223 fb$^{-1}$data sample collected with the Belle detector at the KEKB $e^+ e^-$ collider.The differential cross sections are fitted in the energy region 1.7 GeV $< W <$2.5 GeV to confirm the two-photon production of two pions in the G wave. In thehigher energy region, we observe production of the $\chi {c0}$ charmonium stateand obtain the product of its two-photon decay width and branching fraction to$\pi^0\pi^0$. We also compare the observed angular dependence and ratios ofcross sections for neutral-pion and charged-pion pair production to QCD models.The energy and angular dependence above 3.1 GeV are compatible with thosemeasured in the $\pi^+\pi^-$ channel, and in addition we find that the crosssection ratio, $\sigma\pi^0\pi^0-\sigma\pi^+\pi^-$, is $0.32 \pm 0.03 \pm0.05$ on average in the 3.1-4.1 GeV region.

Autor: S. Uehara, et al. Belle Collaboration

Fuente: https://arxiv.org/