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Heavy Quarks: lessons learned from HERA and Tevatron

“…Even more, when matching charm and bottom across their thresholds, they start from negative values as illustrated in Figure 8. The matching conditions have been computed by a number of groups, [27,28] and at NNLO PDFs will have discontinuities of order O(α 2 S ) when we transition from N F to N F + 1 avors. While we may be uncomfortable with discontinuities in our PDFs, we are reminded that the PDFs are not physical observables, but instead are only theoretical constructs which depend on (arbitrary) renormalization schemes and scales.…”

Summary of working group I: Hadron structure

“…Similar aspects were considered before as well in [10] applying the coefficient functions [21] in a scenario based on three light flavors. During the last year more theoretical calculations of the heavy flavor contributions to both the structure functions in neutral and charged current deep inelastic scattering were performed [24][25][26] and others are in progress [27]. The data on F cc 2 (x, Q 2 ) will further improve as more luminosity is collected.…”