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Hi Henning, OK, let me summarize the current status of the fits and why I think that the latest version of the Vub conf. paper is now completely consistent. I will answer to your other points in detail below as well. First, I think that we need to be consistent within a given theory, but we can't apply comments from a group of theorist to another theory. I guess it is clear by now to everyone in this mailing list that there are two different ways to extract shape parameters from the photon spectrum, either fitting the photon spectrum or extracting the information from the corresponding photon energy moments. We know (although you do not mention explicitely in your email) that Bigi and Uraltsev do not agree in fitting the spectrum with their predictions but they do only trust the moments. I think that the current Vub paper is perfectly consistent in using the moments for this scheme. There is also the BLNP approach that supports the fit to the spectrum and the current Vub paper uses the fit to the spectrum within this approach. Now, any statement from BBU concerning the fact that the fit to the spectrum is not valid, has only to be applied to their own theory. How can we tell theorists who do different calculations what they should be using? On Wed, 3 Aug 2005, Henning Flaecher wrote: > > Hi Francesca, > > > Hi Henning, an addition. If one does the global fit in the BLNP scheme and > > adds the results from the fit to the spectrum (within which scheme they > > are consistent), the errors on the parameters are going to be very small. > > I'm not sure what you mean by global fit in BLNP scheme. There exist no > calculations for b->clv in this scheme and I'm pretty sure they won't for > a while. What Neubert is refering to is to use the calcualtions in > the kinetic scheme, relate the parameter definitions to those in the SF > scheme and then re-expand the expressions consistently in alpha_s and > 1/mb. But this is pretty much the same as to fit in the kin scheme and > then translate the results too the SF scheme. yes, but in the BLNP scheme we can then combine the fit to the b2clnu moments with a fit to the spectrum. This part is still missing. > > > That has not been yet tried. Note moreover, that > > the fit to the spectrum in BaBar gives results much better than from > > Belle. > > But here we again encounter the problem of model dependence. The Belle > spectrum is much less sensitive to the influence of the K* peak as it is > measured in the Y(4S) and therefore this is smeared out and so I would > not expect that from a fit to the spectrum you get the same results. The > moments however which qre not so sensitive to the differential spectrum > agree pretty well. The fact that the fit to the spectrum from the Babar > semi-excl analysis agrees so well with the clv moments could just be a > coincidence. We have already shown in the past that we (BaBar) are not sensitive to the K* shape and transition point. Again, I remark that I believe that the best way to present results is to show what we get. Everyone has now understood that there are different theoretical schemes on the market. Best-practise I think is to present our results consistently with those schemes and not applying comments valid in a scheme to another. On Wed, 3 Aug 2005, Henning Flaecher wrote: > > > > 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. I do agree that the difference between the shape function models has to be considered as contribution to the theoretical errors. They are in the paper indeed for being treated as such. > (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.) Who made this statement? Where is it referenced? We can't really continue just getting private communications from theorists complaning about other theorists... they need to support they comments with papers and then we can take them into account. > 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. > Of course, we all agree with this statement... We are just coping with the fact we have experiment cuts. Cheers, Francesca