Measurement of $D^{\ast \pm}$ production and the charm contribution to $F_2$ in deep inelastic scattering at HERA

Abstract.

The production of $D^{\ast \pm}$(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb$^{-1}$. The decay channels $D^{\ast +}\rightarrow D^0 \pi^+$ (+ c.c.), with $D^0 \rightarrow K^- \pi^+$ or $D^0 \rightarrow K^- \pi^- \pi^+ \pi^+$, have been used to identify the D mesons. The $e^+p$ cross section for inclusive $D^{\ast \pm}$ production with $1 < Q^2 < 600\,$GeV$^2$ and $0.02< y < 0.7$ is $8.31 \pm 0.31 \mbox{(stat.)}^{+0.30}_{-0.50}\mbox{(syst.)}$ nb in the kinematic region $1.5 < p_T(D^{\ast \pm}) < 15$ GeV and $|\eta(D^{\ast \pm})| < 1.5$. Differential cross sections are consistent with a next-to-leading-order perturbative-QCD calculation when using charm-fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in $p_T(D^{\ast \pm})$ and $\eta(D^{\ast \pm})$ in order to determine the charm contribution, $F_{2}^{c\bar c}(x,Q^2)$, to the proton structure function. The ratio $F_{2}^{c\bar c}/F_{2}$ rises from $\simeq$10% at $Q^2 \simeq$ 1.8 GeV$^2$ to $\simeq$30% at $Q^2 \simeq$130 GeV$^2$ for x values in the range $10^{-4}$ to $10^{-3}$.