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
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.