Experimental Investigation of the Two-Photon Widths of the $χ_{c0}$ and the $χ_{c2}$ Mesons

Using 12.7 $fb^{-1}$ of data collected with the CLEO detector at CESR, we observed two-photon production of the $c \bar c$ states $\chi_{c0}$ and $\chi_{c2}$ in their decay to $\pi^+ \pi^- \pi^+ \pi^-$. We measured $\Gamma_{\gamma\gamma}(\chi_{c}) \times {\mathcal B}(\chi_{c} \to \pi^+\pi^-\pi^+\pi^-)$ to be 75 +- 13 (stat) +- 8 (syst) eV for the $\chi_{c0}$ and 6.4 +- 1.8 (stat) +- 0.8 (syst) eV for the $\chi_{c2}$, implying $\Gamma_{\gamma\gamma}(\chi_{c0})$ = 3.76 +- 0.65 (stat) +- 0.41 (syst) +- 1.69 (br) keV and $\Gamma_{\gamma\gamma}(\chi_{c2})$ = 0.53 +- 0.15 (stat) +- 0.06 (syst) +- 0.22 (br) keV. Also, cancelation of dominant experimental and theoretical uncertainties permits a precise comparison of $\Gamma_{\gamma\gamma}(\chi_{c0})/\Gamma_{\gamma\gamma}(\chi_{c2})$, evaluated to be 7.4 +- 2.4 (stat) +- 0.5 (syst) +- 0.9 (br), with QCD-based predictions.