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Vub measurement using recoil of fully reconstructed Bs

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Subject:
From:
Kerstin Tackmann <[log in to unmask]>
Date:
18 Apr 2006 14:15:58 -0700 (PDT)Tue, 18 Apr 2006 14:15:58 -0700 (PDT)
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Hi all,

I have a question concerning the correction we apply to reweight the MC
to have the same ratio of charged to neutral B as data.

More precisely, we apply this correction to all types of MC (signal,
b->clnu, other) and we really only use the same sign events for the
neutral B decays.

Here is what I wonder about: When we do the mixing correction (see BAD
540 section 5.2.1), we assume that among the neutral B, all the leptons
we call signal leptons arise from direct (B->Xclnu) and from cascade
decays, mixed and unmixed in both cases. In signal MC, we will not have
any cascade leptons from D decays, so the ratio between same sign and
opposite sign events will be different in signal MC and in b->clnu MC
and in data.
This means that also the ratio between charged B and same sign neutral B
events will be different in data (which, with the few cuts applied here,
will be mostly b->clnu and hence has cascade leptons from D) and signal
MC. Yet we reweight the signal MC to have the same ratio.
So it seems we take the cascade leptons into account for the mixing
correction, but not for the correction between charged and (same sign)
neutral B decays. Was there an explicit decision to do it this way?
If so, why? Does whoever implemented it this way remember the reasoning
behind this?

I stumbled over this when I went through the VVF code to see how this
correction should be applied to the spectral unfolding specific
data sets. However, this seems relevant for the BRBR extraction as well.

Thanks,
Kerstin




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