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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2009, vol. 79, p. -

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

Uehara S., Watanabe Y., Nakazawa H., Aihara H., Arinstein K., Aulchenko V., Bakich A. M., Barberio E., Belous K., Bhardwaj V., Bondar A., Bozek A., Bračko M., Browder T. E., Chen A., Cheon B. G., Chistov R., Cho I. S., Choi S. K., Choi Y., Dash M., Eidelman S., Epifanov D., Gabyshev N., Goldenzweig P., Ha H., Haba J., Han B. Y., Hayasaka K., Hayashii H., Hazumi M., Hoshi Y., Hou W. S., Hyun H. J., Inami K., Ishikawa A., Iwasaki Y., Joshi N. J., Kah D. H., Katayama N., Kawasaki T., Kichimi H., Kim H. O., Kim Y. I., Kim Y. J., Korpar S., Križan P., Krokovny P., Kuzmin A., Kwon Y. J., Lee M. J., Lesiak T., Liu Y., Liventsev D., Louvot R., McOnie S., Miyata H., Mizuk R., Nagasaka Y., Nakao M., Nishida S., Nishimura K., Nitoh O., Ogawa S., Ohshima T., Okuno S., Pakhlov P., Pakhlova G., Park C. W., Park H., Park H. K., Pestotnik R., Piilonen L. E., Poluektov A., Sahoo H., Sakai Y., Schneider O., Senyo K., Shapkin M., Shiu J. G., Shwartz B., Starič M., Sumiyoshi T., Tanaka M., Teramoto Y., Tikhomirov I., Uglov T.

The differential cross sections for the process γγ→π 0π0 have been measured in the kinematic range 0.6GeV<W<4.1GeV, |cos θ*|<0.8 in energy and pion scattering angle, respectively, in the γγ center-of-mass system. The results are based on a 223fb-1 data sample collected with the Belle detector at the KEKB e+e- collider. The differential cross sections are fitted in the energy region 1.7GeV<W<2. 5GeV to confirm the two-photon production of two pions in the G wave. In the higher-energy region, we observe production of the χc0 charmonium state and obtain the product of its two-photon decay width and branching fraction to π0π0. We also compare the observed angular dependence and ratios of cross sections for neutral-pion and charged-pion pair production to QCD models. The energy and angular dependence above 3.1 GeV are compatible with those measured in the π+π- channel, and in addition we find that the cross section ratio, σ(π0π0)/σ(π+π-), is 0.32±0.03±0.05 on average in the 3.1-4.1 GeV region. © 2009 The American Physical Society.