Well, that's easy to explain. Since we are just summing the four momemta
of the measured objects there will be e.g. a costheta dependence for
losing objects and hence losing energy. Simple error propagation
will not include this in the error definition of the X-system. All missing
energy will be blamed on the neutrino ... and that's not what we want.
Therefore, we probably will need a (costheta,energy) dependent correction
for losing objects on top of the simple sum of cov matrix.

Or, if this does not work, we might consider to optimize only the
direction measurement of the X-system and assume the energy of X unmeasured
in the fit. This will reduce NDF by one and the 2C(3C) will become
1C(2C) but it still should work .... I have already tested this for tau
reconstructions where you have similar problems.

Anyhow, as I said, that's just the beginning .... .


Oliver


On Tue, 6 Nov 2001, Riccardo Faccini wrote:

> given  we are just taking X to be the sum of the four momemta we can just
> add covariance matrices. What is your perplexity?
> 	ciao
> 	ric
>
> ______________________________________________________
> Riccardo Faccini
>  U.C. San Diego, Universita' "La Sapienza" & I.N.F.N. Roma
> tel  +39/06/49914338 http://www.slac.stanford.edu/~rfaccini
> Univ. La Sapienza. 2,Ple Aldo Moro, I-00100 Roma
> Dipartimento di Fisica
>
> "A voice said to me: 'smile and be happy, things could be worse'. I smiled
> and was happy and indeed things got worse" (an office in Ferrara)
>
>
>
> On Tue, 6 Nov 2001, Oliver Buchmueller wrote:
>
> >
> > Correct, so far I am using an "overall cov matrix"
> > for the event. However, technically the usage of event-by-event errors
> > is foreseen and (hopefully) it should improve things even further
> > - but not yet sure how to apply the event-by-event
> >   stuff to the X-system ... a bit more brain power has to go into
> >   this ..thought -
> >
> > Oliver
> >
> >
> > On Tue, 6 Nov 2001, Riccardo Faccini wrote:
> >
> > > Great!
> > > If I understand correctly you have not yet exploited the candidate by
> > > candidate information which is now in the ntuple, that could improve the
> > > situation (in particular the tails), correct?
> > >
> > > I will read the document more carefully later.
> > > 	thanks
> > > 	ric
> > > ______________________________________________________
> > > Riccardo Faccini
> > >  U.C. San Diego, Universita' "La Sapienza" & I.N.F.N. Roma
> > > tel  +39/06/49914338 http://www.slac.stanford.edu/~rfaccini
> > > Univ. La Sapienza. 2,Ple Aldo Moro, I-00100 Roma
> > > Dipartimento di Fisica
> > >
> > > "A voice said to me: 'smile and be happy, things could be worse'. I smiled
> > > and was happy and indeed things got worse" (an office in Ferrara)
> > >
> > >
> > >
> > > On Tue, 6 Nov 2001, Oliver Buchmueller wrote:
> > >
> > > >
> > > > Dear All,
> > > >
> > > > as promised, the technical development of a
> > > > kinematic fit for semileptonic B events is
> > > > now finalized. All technical aspects have been
> > > > tested successfully (e.g. zero mass for neutrino,
> > > > overall constraint fullfillment,...).
> > > > The fit uses the whole event information including
> > > > not only the leptonic B decay but also the fully
> > > > reconstructed B candidate on the "other side".
> > > > Hence, not only energy momentum conservation but
> > > > also additional mass constraints like Equal Mass
> > > > or B Mass hypothesis can be used.
> > > >
> > > > For those who might be interested in details,
> > > > I have made a short node describing the technical
> > > > and physical aspects of this tool. Some performance
> > > > test are also shown in this note.
> > > >
> > > > The note can be found in:
> > > > http://www.slac.stanford.edu/~buchmuel/B-xlv_kinfit.ps
> > > >
> > > > This test indicates that's variables build out of
> > > > information from X-system AND neutrino (missing momentum)
> > > > are the most promising once in terms of "resolution improvements".
> > > > The results also suggest that more work has to
> > > > invested in the improvement of the X-system reconstruction
> > > > because it seems to be the limiting part in the
> > > > kinematic reconstruction.
> > > >
> > > >
> > > > I am looking forward to see your reaction/remarks/comments.
> > > >
> > > > Cheers,
> > > >
> > > > Oliver
> > > >
> > > >
> > > > By the way,
> > > >
> > > > this is clearly not the final word concerning kinematic fitting
> > > > of the semileptonic events ... it more supposed to be a start ...!
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>