Closed enocera closed 2 years ago
Let me try to go back to this.
@scarlehoff I think that I now understand the origin of the ~54 factor. We must rescale the Vrap result by $\sqrt{2s}$. With $\sqrt{s}=38.76$ GeV being the c.m.e. of both DYE605 and DYE866, one has $\sqrt{2s}=54.81$ GeV. I'll write the explanation of this in detail later, for the time being please rescale the Vrap result by a factor $\sqrt{2s}$ by default (this also applies to the ratio observables, though of course there it is immaterial because of the num/den simplification).
The factor works perfectly, although with this factor the agreement is a bit worse (now the agreement between apfel and vrap is at worst 1.2% instead of being below 1% all across -with 54.35-).
Which, I think, is a mater of life. Note that there may be other sources for this "discrepancy", such as different values of the physical parameters (such as MZ), as @cschwan noted yesterday, or in the pbarn conversion factor, as noted in #9 .
Are all the input parameters the same between APFEL and Vrap?
The pbarn conversion is fixed. The factors hardcoded in vrap now are all using the latest edition of the PDG (but this might not be the case for apfel!) But yes, I think we can live with 1.2% :P
OK, but are these values consistent between APFEL and Vrap? I'd say no (so this may explain the difference). Question: are you taking the value of $\sqrt{s}$ from the commondata? I've taken $\sqrt{s}=38.76$ from the paper, BUT I haven't checked that this is the SAME as int he commondata. Actually, the commondata implementation of the old FT DY data (everything but DYE906) is a mess...
Sorry - I see that the values are not as in APFEL, you've said this explicitly!
Actually, the commondata implementation of the old FT DY data (everything but DYE906) is a mess...
Well, about DYE906, turns out that the fktable expect a jacobian factor computed with $\sqrt{s} = 38.76$. Of course, it "doesn't matter" because we always use it as a ratio...
As reported in https://github.com/scarlehoff/Hawaiian_vrap/issues/6, cross sections computed with Vrap+PineAPPL differ from the available FK tables computed with APFEL+APFELComb. Here is a summary of my understanding.