Hi Francesca,

-- I'll put this one to the vub-recoil list, too, so others can contribute
if they wish... --

> > > as I mentioned at today's meeting, I just want to bring up how we did the
> > > truth-match in the b->sgamma analysis (that we call indeed pseudo
> > > truth-matching).
> > >
> > > The details are on BAD 768, v16, section 7.6. We distinguish between the
> > > fully truth matched events (for which all the daughters are truth matched
> > > to the B), and the onces which are not fully truth
> > > matched (where the reconstructed track have an associated GHit, and the
> > I am not sure I understand what you mean (I also read the part in BAD
> > 786). I assume you mean you do not require every track to be truth
> > matched using the standard truth matching (I think there a track is called
> > truth matched if the true track caused the majority of the hits that
> > are making up the reco track.). I guess you do *not* mean that your first
> > category leaves out tracks once they have a single hit that is not
> > truth matched to the right particle. Is this correct?
> > The "have an associated GHit" is the formulation that is confusing me...
>
> yes, you are right. We say in the BAD 'associated GHit', but we actually
> mean truthmatched track, with whatever is the number of GHits required.
>
> >
> > > reconstructed final state is the same than the true final state), and for
> > > which the reconstructed hadronic mass is within 50(25) MeV away from the
> > > true one.
> > > The sum of all the events makes the whole of the pseudo truth matched
> > > events.
> > >
> > > In our case, this method worked well. Could it be feasible for the
> > > semileptonic events? Do you see any drawback?
> >
> > Requiring the modes of the true and the reco'd B was actually our
> > previous truth matching and we found this too strict for the
> > 2 PDF mES fit, we need to be looser than this.
> >
>
> What actually we had in b2sgamma are:
> -fully truth-matched events: the tracks are truthmatched and asked to come
> from the true B
> - "pseudo-truthmatched" events: the tracks are truthmatched, the recoed
> final states is asked to be identical to the true B final state (we do
> not ask that the tracks come from the true B), a cut on
> mX is applied. The events which fail the cut are our cross-feed
> background, which mainly means a peaking background.
>
> We take all the events which pass at least one of the two criteria.
>
> We had at most 4 particles in the final state plus the gamma.
>
> > Concerning looking at the reco'd mass:
> > So in our case we would look at the difference of the generated and
> > reco'd mES if we wanted to follow this method as closely as possible?
> > I guess we could try that, however, I wonder if it is a good idea.
> > Loosely, this would mean to restrict the truth matching to about the
> > mES signal region. While this would probably allow us to get a truth
> > matching that looks nicer (I did look at this in December), we loose
> > the mES tail for telling us how well we really do.
> >
> > Does this seem to make sense?
>
> I think one needs to look at the difference between the true and the
> reconstructed mass and see how close there are. It could be that one
> doesn't really lose the tails of the events if the cut is wide enough. BTW, the
> cut should be dependent on the number of particles of the hadronic system.
>
> However, I really have the suspicion that if one applies this method will
> necessarily have a peaking background, so most likely will need to go back
> to the 3D PDF.

Yes, probably. However, from the studies Antonio showed earlier this
year we concluded that even on the high statistics samples the 3 PDF fit
was unstable and if I am not mistaken we decided that we were going to
abandon this approach...

I think it makes more sense if we first fix our fit strategy and then
find the best possible truth matching and not vice versa...


> Kerstin: where can I find your study regarding the mass cut?

Unfortunately, there is nothing I can point to. I just played with
this a little and did not keep the results... sorry. While it looked
nicer, it did not seem very sensible, since by just cutting at mES
I was free to do whatever I wanted and it seemed too arbitrary to
me. Your cut on the difference makes more sense to me, so we should
rather try that I think.

> > But I do think that an improvement of the current truth matching
> > is more than welcome!
> >
> > Maybe it would be useful to move this discussion to the vub-recoil
> > list to allow other people to contribute/follow.
>
> OK, I will forward all the emails to the mailing list.
>
> Unfortunately I will have another meeting starting at 8:00 on Tuesday so I
> am not sure I will manage to attend the vub-recoil meeting.
> If not possible, can I just call you and/or whoelse is interested
> to have a chat on Tuesday after the meeting? I guess I would be
> free only around 10:00-10:30.

I have time until 11:00am. So we could do it until 11:00am, if we
think that's enough time to start or we can do it on Wednesday or
another day this week.

Cheers,
Kerstin