# Formation of the $\eta_c$ in Two-Photon Collisions at LEP

3 CMS
IP2I Lyon - Institut de Physique des 2 Infinis de Lyon
Abstract : The two-photon width $\Gamma_{\gamma\gamma}$ of the $\eta_{\mathrm{c}}$ meson has been measured with the L3 detector at LEP. The $\eta_{\mathrm{c}}$ is studied in the decay modes $\pi^+\pi^-\pi^+\pi^-$, $\pi^+\pi^-$K$^+$K$^-$, K$_s^0$K$^\pm\pi^\mp$, K$^+$K$^-\pi^{0}$, $\pi^+\pi^-\eta$, $\pi^+\pi^-\eta'$, and $\rho^+\rho^-$ using an integrated luminosity of 140 pb$^{-1}$ at $\sqrt{s} \simeq 91$ GeV and of 52 pb$^{-1}$ at $\sqrt{s} \simeq 183$ GeV. The result is $\Gamma_{\gamma\gamma}(\eta_{\mathrm{c}}) = 6.9 \pm 1.7 \mbox{(stat.)} \pm 0.8 \mbox{(sys.)} \pm 2.0$(BR) keV. The $Q^2$ dependence of the $\eta_{\mathrm{c}}$ cross section is studied for $Q^2 < 9$ GeV$^{2}$. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a $\rho$-pole. In addition, a signal of $29 \pm 11$ events is observed at the $\chi_{\mathrm{c}0}$ mass. Upper limits for the two-photon widths of the $\chi_{\mathrm{c}0}$, $\chi_{\mathrm{c}2}$, and $\eta_{\mathrm{c}}'$ are also given.
Document type :
Journal articles

http://hal.in2p3.fr/in2p3-00003666
Contributor : Sylvie Flores <>
Submitted on : Wednesday, November 3, 1999 - 10:22:25 AM
Last modification on : Friday, December 4, 2020 - 1:22:16 PM

### Citation

M. Acciarri, P. Achard, O. Adriani, M. Aguilar-Benitez, J. Alcaraz, et al.. Formation of the $\eta_c$ in Two-Photon Collisions at LEP. Physics Letters B, Elsevier, 1999, 461, pp.155-166. ⟨in2p3-00003666⟩

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