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

TL;DR

This study measures the two-photon decay widths of the $ ext{\chi}_{c0}$ and $ ext{\chi}_{c2}$ mesons using data from the CLEO detector, providing precise experimental values to compare with QCD predictions.

Contribution

It provides the first precise measurements of the two-photon widths of $ ext{\chi}_{c0}$ and $ ext{\chi}_{c2}$ mesons, including their ratio, enabling tests of quantum chromodynamics models.

Findings

Measured $ ext{\Gamma}_{\gamma\gamma}( ext{\chi}_{c0})$ = 3.76 ± 0.65 ± 0.41 ± 1.69 keV.

Measured $ ext{\Gamma}_{\gamma\gamma}( ext{\chi}_{c2})$ = 0.53 ± 0.15 ± 0.06 ± 0.22 keV.

Ratio $ ext{\Gamma}_{\gamma\gamma}( ext{\chi}_{c0})/ ext{\Gamma}_{\gamma\gamma}( ext{\chi}_{c2})$ = 7.4 ± 2.4 ± 0.5 ± 0.9.

Abstract

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.