9,609 research outputs found

    Have we seen anything beyond (N)NLO DGLAP at HERA?

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    The evidence from HERA for parton saturation, and other low-xx effects beyond the conventional DGLAP formalism, is recalled and critically reviewed in the light of new data and analyses presented at the conference.Comment: 4 pages, 5 figures, Contribution to the discussion session at Intenrational Symposium on Multiparticle Dynamics, ISMD08, Hambur

    Extraction of the proton parton density functions using a NLO-QCD fit of the combined H1 and ZEUS inclusive DIS cross sections

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    The combined HERA-I data set, of neutral and charged current inclusive cross-sections for e+pe^+p and eβˆ’pe^-p scattering, is used as the sole input for a next-to-leading order (NLO) QCD parton distribution function (PDF) fit. The consistent treatment of systematic uncertainties in the joint data set ensures that experimental uncertainties on the PDFs can be calculated without need for an increased Ο‡2\chi^2 tolerance. This results in PDFs with greatly reduced experimental uncertainties compared to the separate analyses of the ZEUS and H1 experiments. Model uncertainties, including those arising from parametrization dependence, are also carefully considered. The resulting HERAPDFs have impressive precision compared to the global fits.Comment: 5 pages, 2 figures. Talk on behalf of H1 and ZEUS collaborations, to be published in the Proceedings of the 16th Workshop on Deep Inelastic Scattering, DIS2008, London, April 7-11th 200

    HERA Collider Results

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    The final results on the combination of all inclusive deep-inelastic scattering cross section data from the H1 and ZEUS experiments at HERA are reviewed. The parton distribution functions (PDFs) extracted from these data (HERAPDF2.0) and from HERA data on heavy flavour production and jet production are also presented (HERAPDF2.0Jets). The use of various heavy flavour schemes is compared and the sensitivity of the data to cuts on Q2 is explored. When jet data are included in the fits, a competitive value of Ξ±s(MZ)=0.1184Β±0.0016\alpha_s(M_Z)=0.1184 \pm 0.0016 is extracted at NLO, excluding scale uncertaintiesComment: Plenary talk at the XXIII International Workshop on Deep-Inelastic Scattering, 27th April-1st May 2015, Dallas, Texas. 14 pages, 18 figures. Based on the analysis of the H1 and ZEUS collaboration

    Including heavy quark production in ZEUS-PDF fits

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    At HERA heavy quarks may contribute up to 30% of the structure function F2F_2. The potential of including heavy-quark data in the ZEUS PDF fits is explored, using Dβˆ—D^* double differential cross-sections as well as the inclusive quantities F2ccΛ‰F_2^{c\bar{c}}, F2ccΛ‰F_2^{c\bar{c}}. The introduction of heavy quarks requires an extension of the DGLAP formalism. The effect of using different heavy flavour number schemes, and different approaches to the running of Ξ±s\alpha_s, are compared.Comment: 4 pages, 4 figures. To be published in the Proceedings of the 16th International Workshop on Deep Inelastic Scattering, DIS2008, London, April 7-11th 200
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