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VUB-RECOIL  December 2009

VUB-RECOIL December 2009

Subject:

RE: Analysis status

From:

Marcello Rotondo <[log in to unmask]>

Date:

17 Dec 2009 14:30:19 +0100 (CET)Thu, 17 Dec 2009 14:30:19 +0100 (CET)

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Hi all,

I want just add my thought about the scaling we need to apply to the D* or 
D** component to get a good chi2 in the final fit.
The fact that fitting the depleted sample with the D* free, we need to 
rescale the D* up by a large amount, does not means we are measuring a 
larger B->D*.

As shown at the Coll. Meeting, fitting the Depleted sample with the D** 
free, you get also un "unreasonble result" because the fit prefer to 
reduce the D** fraction by ~30% when you know there are missing 
components. But also in this case we are going in the same direction: 
the D* have to increased. (I have to say here that I agree with kersint 
and I would prefer to fit the D**).

But I want to remind you that in the fit on the Enriched  sample (to 
extract Vub) we have the total Vcb component free in the fit. The fit on 
the Depleted say that the shape need to be adjusted, and the relative 
fraction of the D*/D** have to be increased to get a good chi2. Otherwise 
the chi2 are bad. That all we can say without other inputs.

Cheers,
Marcello




On Fri, 11 Dec 2009, Luth, Vera G. wrote:

> 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
>


+------------------------------------------------------+
    Marcello Rotondo
    INFN Sezione di Padova, Dipartimento di Fisica
    Via Marzolo, 8
    35131 Padova - Italy
    Tel  : +390498277047
    Fax  : +390498277102
    Email: [log in to unmask], [log in to unmask]
+------------------------------------------------------+




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