Measurement of two-photon decay width of χ_c2(1P) in γγ → χ_c2(1P) → J/ψγ at Belle

We report the measurement of the two-photon decay width of χ _ c 2(1 P ) in two-photon processes at the Belle experiment. We analyze the process γγ → χ _ c 2(1 P ) → 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 χ _ c 2(1 P ) and the branching fraction is determined to be Γ γγ χ c 2 1 P B χ c 2 1 P → J / ψγ B J / ψ → ℓ + ℓ − = 14.8 ± 0.3 stat . ± 0.7 syst . $$ {\Gamma}_{\gamma \gamma}\left({\chi}_{c2}(1P)\right)\mathcal{B}\left({\chi}_{c2}(1P)\to J/\psi \gamma \right)\mathcal{B}\left(J/\psi \to {\ell}^{+}{\ell}^{-}\right)=14.8\pm 0.3\left(\textrm{stat}.\right)\pm 0.7\left(\textrm{syst}.\right) $$ eV, which corresponds to Γ_ γγ ( χ _ c 2(1 P )) = 653 ± 13(stat.) ± 31(syst.) ± 17(B.R.) eV, where the third uncertainty is from B $$ \mathcal{B} $$ ( χ _ c 2(1 P ) → J/ψγ ) and B $$ \mathcal{B} $$ ( J/ψ → ℓ ^+ ℓ ^ − ).