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