The production of charmonium states from two-photon collisions has been measured and searched for by the Belle Collaboration at the KEKB e+e− collider. In this analysis, the process γγ→X→J/ψγ, J/ψ→ℓ+ℓ−(ℓ=eorμ) is analyzed by using a 971.1 fb−1 Belle data sample, where X is a charmonium state. Previously, Belle and CLEO collaborations have reported measurements of γγ→χc2(1P)→J/ψγ, J/ψ→ℓ+ℓ− using 32.6 fb−1 and 14.4 fb−1 data samples, respectively. By analyzing an about 30 times larger data sample, we perform a more precise measurement of the χc2(1P) and search for other charmonium(-like) states. From the Monte Carlo samples the detection efficiency is estimated to be 7-15% under some conditions. Also shown are the results of a feasibility study using a signal MC sample from which the expected accuracy for a measurement of the χc2(1P) is evaluated.
We obtain Γγγ(χc2(1P))B(χc2(1P)→J/ψγ)B(J/ψ→ℓ+ℓ−)=13.5±0.2 (stat.)±0.5(syst.) eV. It turns out that the statistical error will be 1.5%. This result is 6.5 times more precise than the previous one.
