Inclusive production of D\(^{\ast\pm}\) mesons in photon-photon collisions at \(\sqrt{s}_{\rm ee}=183\) and 189 GeV and a first measurement of \(F^\gamma _{2,{\rm c}}\)

The inclusive production of \({{\rm D}^{\ast\pm}}\) mesons in photon-photon collisions has been measured using the OPAL detector at LEP at \(\mboxe^+\mboxe^-\) centre-of-mass energies \(\sqrt{s_{\rm ee}}\) of 183 and 189 GeV. The \({{\rm D}^{\ast+}}\) mesons are reconstructed in their decay to \({\rm D}^0\pi^+\) with the \({\rm D}^0\) observed in the two decay modes \({\rm K}^-\pi^+\) and \({\rm K}^-\pi^+\pi^-\pi^+\). After background subtraction, \(100.4\pm12.6 (\rm stat)\)\({\rm D}^{\ast\pm}\) mesons have been selected in events without observed scattered beam electron (“anti-tagged”) and \(29.8 \pm 5.9 ({\rm stat}){{\rm D}^{\ast\pm}}\) mesons in events where one beam electron is scattered into the detector (“single-tagged”). Direct and single-resolved events are studied separately. Differential cross-sections \({\rm d}\sigma/{\rm d}p_{\rm T}^{{\rm D}^{\ast}}\) and \({\rm d} \sigma/{\rm d} \vert \eta^{{\rm D^{\ast}}}\vert\) as functions of the \({{\rm D}^{\ast\pm}}\) transverse momentum \(p^{\rm D^{\ast}}_{\rm T}\) and pseudorapidity \(\eta^{{\rm D}^{\ast}}\) are presented in the kinematic region \(2{\rm GeV} < p^{\rm D^{\ast}}_{\rm T} < 12{\rm GeV}\) and \(|\eta^{{\rm D}^{\ast}}|< 1.5\). They are compared to next-to-leading order (NLO) perturbative QCD calculations. The total cross-section for the process \(\mboxe^+\mboxe^- \to \mboxe^+\mboxe^- \mbox c\overline{\mbox c}\) where the charm quarks are produced in the collision of two quasi-real photons is measured to be \(\sigma({\rm e}^+{\rm e}^- \to{\rm e}^+{\rm e}^-{\rm c}\bar{{\rm c}}) = 963\pm 110 ({\rm stat})\pm 86({\rm sys})\pm 224 ({\rm extrapolation}){\rm pb}\). A first measurement of the charm structure function \(F^\gamma _{2,{\rm c}}\) of the photon is performed in the kinematic range \(0.0014 < x < 0.87\) and \(5 {\rm GeV}^2 < Q^2 < 100{\rm GeV}^2\), and the result is compared to a NLO perturbative QCD calculation.