1 / 40

Update on QCD Fits, error estimates

Update on QCD Fits, error estimates. Outlook. Parameterizations Assumptions for central fit Systematics from model dependence Variations Options to be decided. Parameterizations. All based on the same PDF functional form : x f(x) = A x B (1 - x) C (1 + D x + E x 2 +F x 3 )

norman-melton
Download Presentation

Update on QCD Fits, error estimates

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Update on QCD Fits,error estimates H1Z Meeting Joël Feltesse

  2. Outlook • Parameterizations • Assumptions for central fit • Systematics from model dependence • Variations • Options to be decided H1Z Meeting Joël Feltesse

  3. Parameterizations • All based on the same PDF functional form : x f(x) = A xB (1 - x)C (1 + D x + E x2 +F x3 ) • The optimal number of parameters depend on the data set. • The former ‘H1 parameterization’ (H1PDF2K), ‘ZEUS-Jet’, ‘Inbetween’ (EP) have been optimised to the H1-ZEUS combined data set (see previous meetings) H1Z Meeting Joël Feltesse

  4. Comparison between parameterizations H1Z Meeting Joël Feltesse

  5. Comparison between parameterizations H1Z Meeting Joël Feltesse

  6. Additional assumptions for heavy quark • H1 param : s = 0.33 Dbar • ZEUS param : (s + sbar) = 0.2 sea • Wthin the Zero Mass Variable Flavour Number (ZMVFN) • H1 : charmed quark = 0.15 Ubar above threshold. • ZEUS : charmed quark, dynamically introduced by evolution • H1 parameterization: dbar/ubar → 1 as x → 0. • ZEUS param’s : dbar – ubar = fixed function of x • In between : same assumptions as H1 parameterization. H1Z Meeting Joël Feltesse

  7. Choice of parameterization • All parametrizations give an excellent Chi2 / 573 : • Inbetween : 476.3 • H1 param : 479.1 • ZEUS_Jet : 475.6 • Chosen central parameterization : ‘optimized Inbetween’ • Motivations : • Less model dependence on B parameters than in H1 param. • No need for an additional input (ubar-dbar) x distribution as in ZEUS-Jet param • Most conservative errors. • It is inspired by both H1 and ZEUS parameterizations. • The two other parameterizations are considered in the model dependence or in the variations ? H1Z Meeting Joël Feltesse

  8. Central fit uses : • The data sets which we have already been using for our comparisons- not any new MB99 or ZVTX 2000 (low Q2 from H1). • Parameterization : ‘optimized in_between‘ • DGLAP NLO fit based on QCDNUM package • alpha_s = PDG 2006 = 0.1176 • Cuts Q2 = 3.5 GeV2 • Q02 = 4. GeV2 • mc = 1.4 GeV2 • mb = 4.75 GeV2 • fs = 0.33 • fc = 0.15 • ZMVFNS • Chi2 definition : uncorrelated for the 43 errors of the two experiments, but correlated for the 4-procedural errors (here Hessian method, but ZEUS uses offset method) H1Z Meeting Joël Feltesse

  9. Model dependence Each source to be considered as a variation from the central job. • Q02 = 2.0 GeV2 - 6.0 GeV2 • Q2 min = 2.5 GeV2 - 5.0 GeV2 • mc = 1.3 GeV2 - 1.55 GeV2 • mb = 4.3 GeV2 - 5. GeV2 • fs = 0.25 – 0.40 • fc = 0.10 – 0.20 • Optimized  H1 and New ZEUS_JETS parameterization (debatable) Each systematic effect has been compared between H1 and ZEUS package → Excellent agreement. (one minor issue : Q2 min = 2 (H1) or 2.5 (ZEUS)) Excellent agreement also with QCDFIT (Li et al.) tested on a few key issues. H1Z Meeting Joël Feltesse

  10. Variation of Q02 of the input parameterization H1Z Meeting Joël Feltesse

  11. Variation of the Q2 cut applied to the data H1Z Meeting Joël Feltesse

  12. Variation of the Q2 cut applied to the data H1Z Meeting Joël Feltesse

  13. Variation of fs,the fraction of Dbar strange = fs * dbar H1Z Meeting Joël Feltesse

  14. Variation of fc,the fraction of cbar charm = fc * Ubar H1Z Meeting Joël Feltesse

  15. Variation of mb, the mass of b quark H1Z Meeting Joël Feltesse

  16. Q2 = 4 GeV2 Blue : experimental errorsRed : (exp + model) errors. uv All model dependence with uncertainty on input parametrisation (i.e. 7 sources) dv gluon H1Z Meeting Joël Feltesse

  17. All model dependence without uncertainty on input parametrisation(i.e. 6 sources) H1Z Meeting Joël Feltesse

  18. Q2 = 4 GeV2 Blue : experimental errorsRed : (exp + model) errors. Ubar All model dependence with uncertainty on input parametrisation (i.e. 7 sources) Dbar Sea H1Z Meeting Joël Feltesse

  19. All model dependence without uncertainty on input parametrisation (i.e. 6 sources) H1Z Meeting Joël Feltesse

  20. Variation with Q2 H1Z Meeting Joël Feltesse

  21. Q2 = 10000 GeV2 Blue : experimental errorsRed : (exp + model) errors uv dv gluon Impressive shrinkage of errors at low x H1Z Meeting Joël Feltesse

  22. Q2 = 10000 GeV2 Blue : experimental errorsRed : (exp + model) errors Ubar Dbar Sea H1Z Meeting Joël Feltesse

  23. Variations - not model dependences. Not to be added together in quadrature but shown separately. • use of general mass VFN -like Robert Thorne's or (and) ACOT (not yet ready but not mandatory for preliminary results) • use of alpha_s = 0.1176 +/- 0.002 • use of humpy not straight solution. H1Z Meeting Joël Feltesse

  24. Alpha_s variation +- 0.002 H1Z Meeting Joël Feltesse

  25. Comparison between straight and humpy minima H1Z Meeting Joël Feltesse

  26. All model dependence with uncertainty on input parametrisation without double minima Comparison with humpy solution uv Reminder : two minima have been observed: Chi2 straight = 476.3 / 573 Chi2 humpy = 494.6 / 573 (With original inbetween parameterization) dv gluon H1Z Meeting Joël Feltesse

  27. All model dependence with uncertainty on input parametrisationand on double minima(i.e.8 sources) H1Z Meeting Joël Feltesse

  28. Comparison with published H1 and ZEUS PDFs (2002-2003) Without double minima uncertainty Much narrower Error band ! H1Z Meeting Joël Feltesse

  29. Comparison with published H1 and ZEUS PDFs (2002-2003) With double minima uncertainty H1Z Meeting Joël Feltesse

  30. Comparison with published H1 and ZEUS PDFs (2002-2003) H1Z Meeting Joël Feltesse

  31. Comparison with published H1 and ZEUS PDFs (2002-2003) H1Z Meeting Joël Feltesse

  32. Last result from H1 Package Last result from ZEUS Package New H1/ZEUS combined PDFs with total experimental uncertainty bands plus model uncertainty bands from 6 sources of model variation: AT THE STARTING SCALE Q20 = 4 GeV2 H1Z Meeting Joël Feltesse

  33. New H1/ZEUS combined PDFs with total experimental uncertainty bands plus model uncertainty bands from 6 sources of model variation: AT THE STARTING SCALE Q20 = 4 GeV2 H1Z Meeting Joël Feltesse

  34. New H1/ZEUS combined PDFs with total experimental uncertainty bands plus model uncertainty bands from 6 sources of model variation: AT THE STARTING SCALE Q20 = 4 GeV2 H1Z Meeting Joël Feltesse

  35. Final options to decide today • Q2 min = 2.5 or 2 GeV2 ? • Offset or Hessian for the 4 correlated errors ? • Add parameterizatios uncertainty in model dependence or show it as a variation ? • Add double minima uncertainty in model dependence or show it as a variation ? • Which plots do we want to be stamped by H1 and ZEUS ? H1Z Meeting Joël Feltesse

  36. EXTRA SLIDES H1Z Meeting Joël Feltesse

  37. The sources of procedural errors related to the averaging procedure : • Center of Mass Energy correction • Multiplicative vs additive systematic errors • Uncertainty on correlations between experiments They are at the few permille level across most of kinematic plane (with few exceptions) H1Z Meeting Joël Feltesse

  38. H1Z Meeting Joël Feltesse

  39. H1Z Meeting Joël Feltesse

  40. Results of ZEUS-Jet H1Z Meeting Joël Feltesse

More Related