High-statistics study of ηπ0 production in two-photon collisions
The differential cross section for the process γγ→η π0 has been measured in the kinematic range 0.84GeV<W<4.0GeV, θ*|<0.8, where W and θ* are the energy and π0 (or η) 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. Clear peaks due to the a0(980) and a2(1320) are visible. The differential cross sections are fitted in the energy region 0.9GeV<W<1.46GeV to obtain the parameters of the a0(980). Its mass, width and ΓγγB(ηπ0) are measured to be 982.3-0.7-4.7+0.6+3. 1MeV/c2, 75.6±1.6-10.0+17.4MeV and 128-2-43+3+502eV, respectively. The energy and angular dependences above 3.1 GeV are compared with those measured in the π0π0 channel. The integrated cross section over θ*|<0. 8 has a W-n dependence with n=10.5±1.2±0.5, which is slightly larger than that for π0π0. The differential cross sections show a sin-4θ* dependence similar to γγ→π0π0. The measured cross section ratio, σ(ηπ0)/σ(π0π0)=0. 48±0.05±0.04, is consistent with a QCD-based prediction. © 2009 The American Physical Society.