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Discussion summary
(1) cross-checks of uncertaintes. The apparent mis-match between the HERAPDF result and the H1 analysis [Eur.Phys.J.C77 (2017), 791;arxiv:1709.07251] in the size of experimental uncertainty seems to be largely understood. The main reason is the difference in the cuts on Q2 and scale, followed by differences in the selection of datasets. Further investigations require dedicated comparisons to fits using the H1 procedures.
(2) cross-check of electroweak corrections. Electroweak corrections are applied to jet data. The corresponding XFitter cross section predictions then have to be calculated for pure photon exchange, different from the default settings. The impact on the fits, however, seems to be very small.
(3) update to recent "official" grids. The NNLOJET grids were updated recently. First tests indicate small improvements in the description of high Q2 jets but otherwise consistent results.
(4) how to include charm and beauty data. It was discussed how to use charm and beauty data in the jets fit. It is technically not feasable to have alpha_s, M(c) and M(b) as free parameters in fits of all datasets together (jets+heavy quark+inclusive). The available predictions for such a fit also seem to be inconsistent, e.g. jets are treated as massless. It was thus agreed to use the charm and beauty data only in fits without jets. The best mass parameters M(c) and M(b) and their model variations will be determined in such "auxillary" fits for a reasonable range of fixed alpha_s. The "final" fits with jets and the scan of alpha_s will be done without including the charm and beauty data, but considering the M(c) and M(b) model uncertainties.