Hi Bob,
> > > g) partial widths, since these are directly comparable to theory and
> > > are the same for B+ and B0 up to isospin-breaking effects (but the
> > > partial BFs are not).
> > Why should the rates neccessarily the same? If WA is playing a substantial
> > role then also the rates will significantly different unless the difference
> > in the B+ and B0 is only due to WA effects is compensating this.
> > I always thought it was Pauli Interference making the main part of the
> > lifetime difference though ...
>
> The point here is fairly trivial - the BF are NEVER the same due to the
> lifetime difference. The partial widths are the same up to WA effects.
OK, then it's 100% clear.
> > > 2) We can use moments from b->clnu, b->ulnu and b->sg to constrain the
> > > SF parameters. There are two paths to extracting Vub from this
> > > information that seem to be agreed upon:
> > >
> > > a) fit the shape function parameters on b-->s gamma events and then
> > > apply them to Vub, eventually adding the information from the Vub
> > > moments themselves.
> > >
> > > iii) implement the new Neubert et al. formulas for b->ulnu and b->sg
> > > in our MC generators
> > I'm not sure if this is already taken care of by somebody.
> > Any insight here?
>
> Ric and Masahiro will look into the b->ulnu part, although I'm sure they
> could use help. I think the RadPen group is supplying someone to
> implement the new b->sg generator. We still need some information from
> Neubert for all this.
>
> > > 3) We should use the mathematica notebooks from Neubert et al. to
> > > extract Vub from our partial rates for q2-Ee and the Ee endpoint
> > > (and Mx, if the new MC generator is not ready in time). The notebooks
> > > should be used with the error ellipses derived from the Belle b-->s gamma
> > > moments themselves that are going to be published (allegedly) in two
> > > weeks by Neubert&co themselves.
> > > 6) We should build our hybrid model in a way that preserves the
> > > inclusive values for the <Mx^2> and <Mx^4-<Mx^2>^2> moments
> > That would be a nice feature. Is the procedure already clear how to build
> > the hybrid in this case?
>
> No - ideas here would be welcome.
Could you tell me what the exact starting point in the discussion
was which lead to this suggestion?
> > >
> > > 8) We got no new suggestion on how to better quantify the WA uncertainty;
> > > just the usual comparison of B+/B0 rates in b->ulnu at high
> > > q2 / high Ee / low Mx. Neubert said: "until you have better information
> > > take 3% as the relative error in the B+/B0 semileptonic widths and
> > > assume the full difference is contained in your signal region."
> > > Nobody objected to this. Note that 3% on the difference in total
> > > rates means 1.5% on the average rate, which is more relevant to our
> > > inclusive measurements (except in cases where tagging results in a
> > > significant B+/B0 acceptance asymmetry).
> > Hm, where does the 3% actually come from?
> > E.g. Macro has been playing around with errors of O(20-30%).
> > In this context: where does this large error come from?
>
> If you go back to the original paper by Voloshin (to which nobody seems to
> have added anything of substance) he quote (eqn 9) DBF = 3.9|Vub|^2 =
> 1*10^-4, where DBF = BF(B+->Xlnu) - BF(B0->Xlnu). The sign of the effect
> is unknown. For analyses accepting equal fractions of B+ and B0, the
> effect is 1/2 DBF divided by the average BF(b->ulnu) or roughly
> (1*10^-4)/2 / 25*10^-4 = 2%. If one then assumes that this full 2% is in
> the region accepted by our cuts, then the effect on the BF is 2%/fu and on
> Vub is 1%/fu. It would be nice if someone checked my math....
Got it :-)
BTW: isn't it interesting on its own that all endpoint analyses
show smaller results for Vub compared to q2-El or mX-q^2...?
Maybe we do already see an effect without having separated
explicitely charged and neutral B's...
Cheers,
Heiko
