Parametrisations of QCD Fits

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Parametrisations of QCD Fits

• (A first look)

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• PDF parametrisation x f(x) A xB (1 - x)C (1
  D x F x3 )

H1 1) at low x quark and antiquark are equal
2) all B (quark or antiquark) equal
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Fit assumptions

• The Zero Mass Variable Flavour Number (ZMVFN) is
  used
• The chi2 is the Pascaud-H1 chi2 (next slide)
• H1 param s 0.33 Dbar
• ZEUS param (s sbar) 0.2 sea
• H1 param Q20 4 GeV2
• ZEUS param Q20 7 GeV2
• Q2 min (data) 3.5 GeV2

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At present in H1fitter



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Q2 4. GeV2
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• At low Q2 , model dependence from parametrisation
  larger than fit errors.
• Parametrisation optimised on early data, may not
  be optimal for more precise data.
• Next steps
• JF and MC, slightly different results for same
  data, same parametrisation to be understood.
• Investigate new parametrisation
• Effect due to Chi2 definition (rel vs abs)
• Investigate NNLO
• Effect on alpha_s
• Inclusive jets
• Effect on EW parameter (?)

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• EXTRAS

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