2 research outputs found

    Parton distribution functions at LO, NLO and NNLO with correlated uncertainties between orders

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    Sets of parton distribution functions (PDFs) of the proton are reported for the leading (LO), next-to-leading (NLO) and next-to-next-to-leading-order (NNLO) QCD calculations. The parton distribution functions are determined with the HERAFitter program using the data from the HERA experiments and preserving correlations between uncertainties for the LO, NLO and NNLO PDF sets. The sets are used to study cross-section ratios and their uncertainties when calculated at different orders in QCD. A reduction of the overall theoretical uncertainty is observed if correlations between the PDF sets are taken into account for the ratio of WW di-boson to Z boson production cross sections at the LHC

    Measurement of D ∗ photoproduction at three different centre-of-mass energies at HERA

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    The photoproduction of D ∗± mesons has been measured with the ZEUS detector at HERA at three different ep centre-of-mass energies s s \sqrt{s} of 318, 251 and 225 GeV. For each data set D ∗± mesons were required to have transverse momentum p T D  ∗ and pseudo-rapidity η D ∗ in the ranges 1 . 9 < p T D  ∗ < 20 GeV and | η D ∗ | < 1 . 6. The events were required to have a virtuality of the incoming photon Q 2 of less than 1 GeV 2 . The dependence on s s \sqrt{s} was studied by normalising to the high-statistics measurement at s = 318 s=318 \sqrt{s}=318 GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the s s \sqrt{s} dependence of the data well
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