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Hi Concezio, > I am not sure I understand your point... the charged/neutral B > correction is applied on B+ montecarlo and takes care of the fact that > the semi-exclusive reconstruction works differently in data and MC. For > instance we don't simulate all the decay modes we reconstruct in data, > so we need to rescale the MC charged/neutral B ratios to what we see in > data. We don't? Not even in the generic BBbar MC? I was not aware of that. > Since we are correcting for Breco effects, we compute the > correction factors at the level of the semileptonic events selection and > carry them over the entire analysis afterwards. Yes, I saw that. I'll try to be a little more precise about what I mean, that was maybe somewhat buried in my lenghty explanation. My worry is the following: To compute this correction factor (between charged and neutral B), only the right sign sample is used for the neutral B. Since there are only requirements on the lepton so far, data is a mixture of b->clnu and b->ulnu, probably much b->clnu, since no of the veto cuts is applied yet. Now the thought about the mixing (not the mixing correction) comes in: b->clnu has cascades, b->ulnu does not have cascades. Therefore, b->clnu has a different ratio of right sign to wrong sign for the neutral B than b->ulnu. Is this correct? Therefore, b->clnu has a different ratio in right sign neutral B events than charged B events. Is this correct? If both these are correct, we expect data (which is dominated by b->clnu at this stage of cuts) to have a different ratio of right sign neutral B events and charged B events than signal MC (and pure b->ulnu data if we had that). Right? Yet, we use this ratio of b->clnu dominated data to reweight the signal MC, although we do not expect the ratio between the two to be the same, based on the signal side. I understand we do this reweighting to correct for things on the tag side, but in order to do this, it seems we need to assume that all the difference (that we even out) comes from the tag side. Unless I am missing something, that assumption does not seem to be justified, since we expect differences on the signal side as well, which are physics and should not be evened out. > The mixing correction is applied on neutral B mesons only, and > separately on data, signal MC and background MC. It is independent on > data/MC yields for charged and neutral Bs. Yes, I saw that in VirUtil. I hope I did a better job explaining what I mean ;-) Does this make more sense? Cheers, Kerstin > Ciao, Concezio. > > PS: tomorrow Italy celebrates the end of WWII, so I guess we won't show > up for the meeting... > > Kerstin Tackmann wrote: > > >Hi, > > > >sorry, I realized that the email below misex up same and opposite sign > >events. We use the ratio between charged events and opposite sign neutral > >events, of course. Sorry about that. > > > >But apart from that, why was it done the way it was? I'd just like > >to understand and see if we should be doing the same... Daniele? Concezio? > > > >Thanks, > >Kerstin > > > > > >On Tue, 18 Apr 2006, Kerstin Tackmann wrote: > > > > > > > >>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 > >> > >> > >> > >> > >