Open charm production in deep inelastic ep-scattering has been measured via its semi-leptonic decay into electrons with the ZEUS detector at HERA using an integrated luminosity of 34pb-1. An integrated cross section, and differential cross sections as functions of W, x and Q2 and of pT and eta of the electron, have been measured and compared to NLO predictions. The charm contribution, F2ccbar, to the proton structure function has been determined and compared with theoretical predictions and with the previous ZEUS measurement based on D*+- production which was made in a more restricted kinematical range.
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Figures:
Figure 1: (a) The dE/dx distributions of the electron-enriched (solid circles) and hadron (open circles) track samples (1 < Q2 < 1000 GeV2, 0.03 < y < 0.7, 1.2 < ptrack < 5.0 GeV and 0.65 < thetatrack < 2.5 rad). The hadron distribution is normalised to the electron-enriched sample in the region 0.8 < dE/dx < 1.1 mips. (b) The dE/dx distribution of the inclusive electron signal (solid triangles) after the statistical subtraction of the hadron and electron-enriched distributions. The number of electrons from photon conversions as found in the data is also shown (open stars). The estimated contribution of background electrons due to Dalitz decays of pi0s and beauty decays is indicated by the dotted and dashed lines respectively.
Figure 2: Differential cross sections as functions of W, x and Q2 and of PT and eta of the electron, in the kinematic region 1 < Q2 < 1000 Gev2 and 0.03 < y < 0.7. The inner error bar of the data points corresponds to the statistical uncertainty, the outer to the combined statistical and systematic uncertainties. The differential cross sections are compared to NLO QCD predictions as calculated with the HVQDIS program, using the GRV94HO proton parton density functions and a charm mass of mc = 1.5 +- 0.2 GeV (shaded band).
Figure 3: The bins used to extract F2ccbar shown on the (x,Q2) plane.
Figure 4: The measured F2ccbar values as a function of x in different Q2 bins. The curves correspond to the theoretical prediction [ref 16] calculated with mc = 1.5 GeV (solid line) and mc = 1.5 +- 0.2 GeV (dotted lines). Also shown are the results from the D* decay channel. The inner error bars of the data points correspond to the statistical uncertainty, the outer to the combined statistical and systematic uncertainties.
Figure 5 Updated Version: The ratio of F2ccbar to F2 as a function of x for different Q2 values. The F2 values are obtained from the ZEUS NLO QCD fit to F2 as described in [ref 17]. The curves correspond to the ZEUS NLO QCD fits. The solid line is obtained using a charm mass of 1.5 GeV, the dotted lines correspond to mc = 1.3 and mc = 1.7 GeV. The inner error bars of the data points correspond to the statistical uncertainty, the outer to the combined statistical and systematic uncertainties.
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