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Hello, > > Hi, > > it seems I have raised an interesting question, the answer to which is > > more articulate than I thought... I propose to write back to Gil > > something like: > > > > ...We feel that the extraction of the shape function parameters from the > > b->sgamma spectrum is more sensitive to remaining theory uncertainties > > and ansaetze for the SF than an approach based on the fit to moments. > > However, we recognize that the debate on this issue is not settled yet > > and we are willing to revisit the above assumption if in case... > > to be honest it is not true. They always supported the fit to the spectrum > since the paper written by Kagan and Neubert (1998). > The question regarding the ansaetze is not valid as we do (as Belle as > well) a fit to the three ansaetzes. > I think that the fair answer is that the paper has to clarify what is used > and not to judge the theory. While it is true that Neubert et al support fits to the spectrum in contrast to other theorists, you do get different answers depending on what shape function ansatz you use (as can be seen from figure 6 of your analysis hep-ex/0508004) and this should be considered when extracting Vub. (In addition there are different opinions on if the shape function is the same in b->ulv and b->sg decays but that probably goes beyond the scope of this discussion.) However, and also Neubert agrees with this, the moments at sufficiently low Ecut are insensitive to the SF as there it is not needed, i.e. a pure OPE ansatz is sufficient. Cheers, Henning >I then think then that the sentence: > > "However, there are concerns that the extraction of the shape function > parameters from the photon spectrum in B->Xs gamma is less reliable" > (p.18 before section 7) > > has to be removed. > The fair thing is to specify that the parameters which are used come from > the fit to the spectrum in the sentence just above that one. > > Again, I am happy to discuss further the issue, but I really believe that > one has to give factual information and not make judgments on the theory. > > Thanks for raising this question, it is important to clarify it... > Francesca >