Measurement of two-photon decay width of xc2(1P) in ??? xc2(1P) ? J/????????i? at Belle

We report the measurement of the two-photon decay width of χc2(1P) in two-photon processes at the Belle experiment. We analyze the process γγ → χc2(1P) → J/ψγ, J/ψ → ℓ+ℓ− (ℓ = e or μ) using a data sample of 971 fb−1 collected with the Belle detector at the KEKB e+e− collider. In this analysis, the product of the two-photon decay width of χc2(1P) and the branching fraction is determined to be Γγγ(χc2(1P))B(χc2(1P)→J/ψγ)B(J/ψ→ℓ+ℓ−)=14.8±0.3(stat.)±0.7(syst.) eV, which corresponds to Γγγ(χc2(1P)) = 653 ± 13(stat.) ± 31(syst.) ± 17(B.R.) eV, where the third uncertainty is from B(χc2(1P) → J/ψγ) and B(J/ψ → ℓ+ℓ−). [Figure not available: see fulltext.].