ZEUS NLO QCD fits

NLO QCD fits using the DGLAP formalism have been made to the high precision ZEUS $e^+p$ reduced cross-section data and to fixed target structure function data, in order to detrmine parton distribution functions and the value of $\alpha_s(M^2_Z)$, taking full account of correlated systematic errors. Preliminary results are reported.Comment: 6 pages,6 figures, accepted by Int. Europhysics Conf. on HEP 2001, Budapes

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

The evidence from HERA for parton saturation, and other low-$x$ 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

The combined HERA-I data set, of neutral and charged current inclusive cross-sections for $e^+p$ and $e^-p$ 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 $\chi^2$ 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

Measurements of αs\alpha_s and parton distribution functions using HERA jet data

Use of HERA jet production cross sections can extend our knowledge of the gluon parton distribution function and yield accurate measurements of $\alpha_s(M_Z)$ in addition to illustrating the running of $\alpha_s$ with scale.Comment: Proceedings of the Ringberg Workshop on `New Trends in HERA Physics 2005

Including heavy quark production in ZEUS-PDF fits

At HERA heavy quarks may contribute up to 30% of the structure function $F_2$. The potential of including heavy-quark data in the ZEUS PDF fits is explored, using $D^*$ double differential cross-sections as well as the inclusive quantities $F_2^{c\bar{c}}$, $F_2^{c\bar{c}}$. 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 $\alpha_s$, 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