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H1/ZEUS averaging meeting Sep 22 nd 2008 A M Cooper-Sarkar Studies on heavy quark scheme LHAPDF implementation.

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Presentation on theme: "H1/ZEUS averaging meeting Sep 22 nd 2008 A M Cooper-Sarkar Studies on heavy quark scheme LHAPDF implementation."— Presentation transcript:

1 H1/ZEUS averaging meeting Sep 22 nd 2008 A M Cooper-Sarkar Studies on heavy quark scheme LHAPDF implementation

2 We need to move to using a General Mass Variable Flavour Number Scheme (GMVFN) rather than our present Zer0 Mass Variable Flavour Number Scheme (ZMVFN) You’ve seen plots from me using a GMVFN before- Robert Thorne’s scheme Labelled as RTVFN. But they were done before we chose the final specifications for our fit So let’s just clear that up first

3 Comparison of central fit plus total uncertainties to variation of heavy quark scheme: using massive variable flavour number scheme of Thorne. LEFT compared to OLDer fit RIGHT compared to HERAPDF0.1 New/Old very similar.

4 Comparison of central fit plus total uncertainties to variation of heavy quark scheme: using massive variable flavour number scheme of Thorne. LEFT compared to OLDer fit RIGHT compared to HERAPDF0.1 New/Old very similar except for very high-x D

5 Now let’s move on to ALL NEW comparisons of GMVFN to ZMVFN On the LEFT comparing HERAPDF0.1 to Thorne’s 2007 GMVFN On the RIGHT comparing HERAPDF0.1 to Thorne’s 2008 GMVFN- NOTE the difference in the gluon

6 Now compare for U D Ubar Dbar On the LEFT comparing HERAPDF0.1 to Thorne’s 2007 GMVFN On the RIGHT comparing HERAPDF0.1 to Thorne’s 2008 GMVFN- not much difference

7 Now compare for ubar dbar sbar cbar On the LEFT comparing HERAPDF0.1 to Thorne’s 2007 GMVFN On the RIGHT comparing HERAPDF0.1 to Thorne’s 2008 GMVFN- not much difference

8 Thorne’s 2007 and 2008 schemes are not that different- but the 2008 one is closer to Voica?- looks pretty consistent -apart from low-x valence- and even this isnt big Thorne says both his schemes are legitimate choices.(as is ACOT), But Thorne 2008 is closer to ACOT also has better χ lower than my standard 476 Since all schemes are legitimate choices, perhaps we will have to live with the small difference between Thoren 2008 and ACOT as a source of model uncertainty? Voica’s plot

9 Progress on LHAPDF implementation Implementation with LHpdf method from parameters by evolution ‘on the fly’ u-valence and d-valence Experimental errors only Compare to our own plots- perfect agreement

10 Implementation with LHpdf method from parameters by evolution ‘on the fly’ u-sea and d-sea Experimental errors only Compare to our own plots- perfect agreement

11 Implementation with LHpdf method from parameters by evolution ‘on the fly’ gluon Experimental errors only Compare to our own plots- perfect agreement

12 Model errors will be done with the LHgrid method Currently checking out agreement of grids with LHpdf method And checking grid interpolation methods Blue line is (LHgrid-LHpdf)/LHpdf for linear interpolation Green line is the same for 4 th order polynomial interpolation Axes are in % - so differences are much less than 0.2% !! Quadratic is better than linear interpolation- important at high-x Red line is linear interpolation but only in Q2 (uses grid points for x) so my grid spacing at high-x is the problem for linear interpolation Agreement gets better as Q2 increases and goes up as Q2 decreases, but is still within 0.2%. We are nearly there!

13 Look just at high-x 0.1 to 1.0 for Q2=10 ans Q2=10000 Linear is only good up to ~0.4 quartic is good up to


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