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PDF fitting to the HERA average data Various comparisons AMCS- January 29 th 2008

PDF fitting to the HERA average data Various comparisons AMCS- January 29 th 2008. Compare ZEUS-JETS/ inbetween/ H1 parametrizations Compare starting Q 2 : Q 0 2 = 4/ Q 0 2 = 2 GeV 2 Compare massless/ massive variable flavour schemes for heavy quark treatment

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PDF fitting to the HERA average data Various comparisons AMCS- January 29 th 2008

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  1. PDF fitting to the HERA average data Various comparisons AMCS- January 29th 2008 • Compare ZEUS-JETS/ inbetween/ H1 parametrizations • Compare starting Q2: Q02 = 4/ Q02 = 2 GeV2 • Compare massless/ massive variable flavour schemes for heavy quark treatment • Compare methods of error treatment in χ2: Quadratic/ Hessian/ Offset

  2. First compare different parametrizations: ZEUS-JETS, ‘inbetween’ and H1 (hopefully Joel has defined these!) in terms of uv, dv, Sea, Glue This page Q2=4 GeV2 other Q2 values in EXTRAS ZEUS-Jets Parametrization in between H1 parametrization Central values are really very similar- quite remarkable since ZEUS and H1 parametrizations are not- however the size of errors differs, with ‘in between’ being the most conservative

  3. Now in terms of U, D, Ubar, Dbar This page Q2=4 GeV2 other Q2 values in EXTRAS ZEUS-Jets Parametrization in between H1 parametrization

  4. Now in terms of ubar, dbar, sbar, cbar This page Q2=4 GeV2 other Q2 values in EXTRAS xubar xcbar xdbar xsbar ZEUS-Jets Parametrization in between H1 parametrization The similarity of these is perhaps even more remarkable given the different treatment of charm- clearly the fixed fraction fc=0.15 is about right compared to dynamical turn on at Q2=mc2

  5. This page Q2=4 GeV2 other Q2 values in EXTRAS Finally in terms of d/u and dbar-ubar ZEUS-Jets Parametrization in between H1 parametrization Here we do see a difference in central values. I like the fact that ‘in-between’ reflects the fact that we don’t know anything!

  6. Now comparing Q02=4 (standard) with Q02=2=mc2 for the ‘inbetween’ parametrization In the latter case the fixed fraction fc=0.0 rather than fc=0.15. One can thus make it fully consistent with dynamical generation. uv,dv,Sea, gluon This page Q2=4 GeV2 Inbetween with Q02=4 Inbetween with Q02=2 Starting at a different Q0 is equivalent to a different parametrization. It will be necessary if we are ever to move to NNLO- it makes charm treatment more rational. Central values fairly similar (d-valence?) error estimates smaller for Q02=2

  7. Now U,D,Ubar,Dbar This page Q2=4 Inbetween with Q02=4 Inbetween with Q02=2 . Central values similar error estimates smaller for Q02=2

  8. ubar, dbar, sbar, cbar This page Q2=4 Inbetween with Q02=4 Inbetween with Q02=2 . Central values similar (high-x dbar?) error estimates smaller for Q02=2

  9. Now d/u and dbar-ubar This page Q2=4 Inbetween with Q02=4 Inbetween with Q02=2 . Error estimates smaller for Q02=2

  10. Return to the standard Q02=4. Stick with ‘inbetween’. Compare dynamical generation of charm zero-mass (ZMVFN) with massive dynamical generation a la Thorne (RTVFN) uv,dv,Sea glue uv,dv,Sea, gluon This page Q2=4 GeV2 Other Q2 in EXTRAS ZMVFN RTFVN Central values similar. Errors fairly similar- larger at low-x for RTVFN

  11. U,D,Ubar,Dbar This page Q2=4 GeV2 ZMVFN RTFVN Central values reflect the fact that charm turns on more slowly- hence less U and Ubar at low-x. Errors slightly larger for RTVFN

  12. ubar,dbar,sbar,cbar ubar,dbar,sbar,cbar This page Q2=4 GeV2 Q2 =10 next page ZMVFN RTFVN RTFVN has a slow turn on of charm the other sea quarks try to compensate to make a similar total Sea

  13. ubar,dbar,sbar,cbar This page Q2=10 GeV2 RTFVN ZMVFN RTFVN has a slow turn on of charm still hasn’t quite caught up at Q2=10.

  14. dbar-ubar and d/u at Q2=4 ZMVFN RTFVN No differences worth remarking on

  15. uv,dv,Sea,gluon This page Q2=4 GeV2 Other Q2 in EXTRAS Now compare methods of treating errors: Quadratic/Hessian/Offset (back to standard fit ZMVFN and ZEUS-JETS parametrization) Offset procedural errors- rest quadratic Quadratic Hessian Central values very similar (not obvious for Hessian) Errors generally largest for OFFSET procedural (high-x dv?), but not much difference compared to using ZEUS data alone- systematic errors not so big now

  16. Procedural seem to be the most significant uv,dv,Sea, gluon This page Q2=4 GeV2 Other Q2 in EXTRAS Offset just procedural errors Offset 27 of the 47 total errors (MINUIT limitations!) procedural are not included here

  17. U,D,Ubar,Dbar This page Q2=4 GeV2 Other Q2 in EXTRAS Offset procedural Quadratic Hessian Central values very similar (not obvious for Hessian) Errors generally largest for OFFSET procedural (high-x D?), but not much difference compared to using ZEUS data alone- systematic errors not so big now

  18. ubar,dbar,sbar,cbar This page Q2=4 GeV2 Other Q2 in EXTRAS Offset procedural Quadratic Hessian Central values very similar (not obvious for Hessian) Errors generally largest for OFFSET procedural, but not much difference compared to using ZEUS data alone- systematic errors not so big now

  19. Conclusions/ to do • Go with some sort of inbetween parametrization • Move to Q02=2 and RTVFN • Use latest data set! • Use either Hessian or OFFSET not quadratic – I favour OFFSET but offsetting all 47 is a pain (even when minuit cooperates). Offsetting the 4 procedural seems the most important. Hessian method does seem to reproduce similar size errors and is more straightforward - ideas? • Agree with Joel on these alternative fits

  20. EXTRAS

  21. in terms of uv, dv, Sea, Glue ZEUS-Jets Parametrization in between H1 parametrization Q2=10 GeV2

  22. in terms of uv, dv, Sea, Glue ZEUS-Jets Parametrization in between H1 parametrization Q2=1 GeV2

  23. Now in terms of U, D, Ubar, Dbar ZEUS-Jets Parametrization in between H1 parametrization Q2=10 GeV2

  24. Now in terms of ubar, dbar, sbar, cbar xubar xcbar xdbar xsbar ZEUS-Jets Parametrization in between H1 parametrization Q2= 10 GeV2

  25. Now in terms of ubar, dbar, sbar, cbar xubar xcbar xdbar xsbar ZEUS-Jets Parametrization in between H1 parametrization Q2= 1 GeV2

  26. Now in terms of ubar, dbar, sbar, cbar This page is all for Q2=1.8225= mc2, not for Q2=1 xubar xcbar xdbar xsbar ZEUS-Jets Parametrization in between H1 parametrization

  27. Finally in terms of d/u and dbar-ubar Q2= 10 GeV2

  28. uv,dv,Sea, gluon This page Q2=10GeV2 Inbetween with Q02=4 Inbetween with Q02=2

  29. uv,dv,Sea, gluon This page Q2=1GeV2 Inbetween with Q02=4 Inbetween with Q02=2

  30. uv,dv,Sea, gluon This page Q2=10 GeV2 ZMVFN RTFVN thompson

  31. uv,dv,Sea, gluon This page Q2=1 GeV2 RTFVN ZMVFN

  32. Procedural seem to be the most significant U,D,Ubar,Dbar This page Q2=4 GeV2 Other Q2 in EXTRAS Offset just procedural errors Offset 27 of the 47 total errors (MINUIT limitations!) procedural are not included here

  33. Procedural seem to be the most significant Ubar,dbar,sbar,cbar This page Q2=4 GeV2 Other Q2 in EXTRAS Offset just procedural errors Offset 27 of the 47 total errors (MINUIT limitations!) procedural are not included here

  34. uv,dv,Sea, gluon This page Q2=10GeV2 Offset procedural Quadratic Hessian Offset 27

  35. uv,dv,Sea, gluon This page Q2=1GeV2 Quadratic Hessian Offset 27

  36. U,D,Ubar,Dbar This page Q2=10GeV2 Offset procedural Quadratic Hessian Offset 27

  37. ubar,dbar,sbar.cbar This page Q2=10GeV2 Offset procedural Quadratic Hessian Offset 27

  38. d/u and dbar-ubar This page Q2=4 GeV2 Other Q2 in EXTRAS Quadratic Hessian Offset 27 Central values very similar (not obvious for Hessian) Errors generally largest for OFFSET procedural, but not much difference compared to using ZEUS data alone- systematic errors not so big now

  39. d/u and dbar-ubar This page Q2=4 GeV2 Other Q2 in EXTRAS Quadratic Hessian Offset 27

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