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Vub measurement using recoil of fully reconstructed Bs

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From:
"Luth, Vera G." <[log in to unmask]>
Date:
11 Dec 2009 11:58:45 -0800Fri, 11 Dec 2009 11:58:45 -0800
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Hello Kerstin,

sorry for the delay in response.
I am somewhat hesitant to offer advice, since I am not 
directly involved.

Here is my 5c of contribution to the discussion:

Clearly your rescaling of the D* rate is unreasonable.
I would fix the Dln, since this BF appears to be solid
and should not be rescaled.
The idea of rescaling the D* is based on the notion that it is the
largest contribution and its BF is poorly known.  So, if you scale D* up
do you downscale down scale D**??
Another approach is to fix the D*ln to the BF measured with the BABAR 
Breco samples. But then how do you fill the rest of the BF?
DO we just leave a gap?  the appears to be difficult to accept,
but may give better results!

Without definite measurements we really are in trouble!

I am afraid, these are very useful comments.  Nothing you do not know!

Ciao
Vera



============================================
Vera Luth
SLAC  - Stanford University
2575 Sandhill Road, Menlo Park, CA 94025 
Phone:  650 926 2702   FAX  650 926 2657
============================================

-----Original Message-----
From: Kerstin Tackmann [mailto:[log in to unmask]] 
Sent: Friday, December 11, 2009 8:51 AM
To: vub-recoil; Lopes Pegna, David; Luth, Vera G.
Subject: Re: Analysis status


Dear all,

should we interpret the silence as that there are no objections to what
we 
are saying/proposing?

Best,
Kerstin

On Tue, 8 Dec 2009, Kerstin Tackmann wrote:

>
> Dear vub-recoilers, conveners, Vera,
>
> we have continued to look into the things we showed at the CM last
month and 
> are getting to a point where we would appreciate feedback on several
points. 
> It would be nice for us to have these clarified before we move on to
produce 
> a measured spectrum with complete systematics, which we will need to
then 
> tune the unfolding. I am hoping that settling on a strategy now that
is 
> supported by the AWG might spare us duplicating work.
>
> (1)
> Is the fitting of a scaling factor for the D** component from the
depleted 
> sample a strategy we are happy enough with? I did try rescaling the D*
> (see the Nov 10 entry here: 
> http://costard.lbl.gov/~kerstin/vubunf/r22/spectrum/spectrum.html),
but given 
> that supposedly we know the D* better (forgetting about the spread in
the 
> different results...) I think I have some preference for
> rescaling the D**, for which our knowledge is more limited.
>
> (2)
> We evaluated another set of systematics to see what the discrepancy
between 
> the fit results for the B->Xclnu scaling factor is that we fit on the 
> signal-enriched and -depleted samples. We go down from 5.5 sigma (stat
only) 
> to 2.3 sigma including a good number of systematics. This page
> http://costard.lbl.gov/~kerstin/vubunf/r22/spectrum/spectrum.html
> has results from a lot of the studies we performed. I am also
attaching a 
> slide that shows the breakdown of the systematics on the scaling
factor 
> difference. If we cannot go ahead with this at this stage, I would
appreciate 
> suggestions for what other studies we should be providing.
>
> (3)
> We are currently only using FF reweighting for B->D*lnu given that mX
should 
> not be very sensitive to FFs. So the only sensitivity we have comes
from the 
> El cut at 1GeV. In the r18 round of the analysis the uncertainties
from the 
> B->D*lnu FF were so low that we did not even quote them. However, we'd
rather 
> include additional reweightings now than later if there are strong
opinions 
> that reweightings for other channels are necessary.
>
> Thanks,
> Kerstin



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