Hi Concezio,
On Wed, 5 Jul 2006, Concezio Bozzi wrote:
> Hi all,
>
> I think there is another issue to be addressed. Up to now, we have been
> worrying about fixing the signal/peaking background components in our
> mES fits, to deal with instabilities in bin of kinematic variables with
> low statistics. We implemented constraints on the signal/peaking
> background components for mES distributions as a function of the bins of
> the kinematical (mx, p+, q2) variables, but only for DATA.
>
> However, our final mx, p+, mx/q2 fits need also distributions for
> Vcb+other MC and Vub(IN+OUT) signal MC. These MC components have been
> and are currently being determined by performing mES fits as usual, e.g.
> by leaving the signal, peaking and combinatorial backgrounds floating
> and without any constraint applied. There are plenty of mES fits on MC
> with low statistics. Recall also that every single bin in the kinematic
> variable under study results from an appropriate sum of mES fits
> performed separately on charged B, neutral B opposite flavor and same
> flavor to correct for BBbar mixing. If you look e.g. at Antonio's
> latest VVF fits in
>
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/
>
> you see that mES fits on data
>
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_data3.eps
> (charged B)
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_data4.eps
> (neutral B opposite flavor)
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_data5.eps
> (neutral B same flavor)
>
> have the peaking/signal fixed (only signal S, combinatorial background B
> and argus shape ar are floating in the fits), whereas the peaking
> background component P is also floating in the MC mES fits:
>
> Vcb+other
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vcboth3.eps
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vcboth4.eps
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vcboth5.eps
>
> VubIN
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vubin3.eps
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vubin4.eps
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vubin5.eps
>
> VubOUT
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vubout3.eps
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vubout4.eps
> http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedmES_vubout5.eps
>
> The bottom line is: we need to constraint somehow the signal/peaking
> background components in the mES fits also for these MC samples. The
> question is: how?
>
> One possible solution is to use the full (charged + neutral B) MC sample
> which has been used to correct for the data, but Antonio showed in his
> previous posting that the fits are not stable for high mx values (signal
> and peaking background are swapped), and are not good for intermediate
> mx values. Grouping several high mx bins seems not to give more stable
> results.
This is of course rather annoying as I would have thought that such a
grouping would help.
A way out could be that we fit the sig/peakBG ratio on the MC-enriched
sample e.g. with a polynomial of order 2 and take this function for the
correction.
BTW: Antonio, does the fit for the second bin which has by far the
smallest error have a good chi^2?
> Another possibility (which can also be applied when constraining S/P =
> signal/peaking on data) is to determine separately S and P, by e.g.
> counting or fitting for S in events with truebrecomode==recobrecomode,
> and fitting ony P and the combinatorial background in events with
> truebrecomode!=recobrecomode. This latter solution should give more
> robust estimates.
This sounds to be a good idea.
Cheers,
Heiko
> In any case, any S/P constraint would be determined on the entire
> (charged+neutral B) sample, and it should be dependent perhaps only on
> the kinematical variables.
> Any comments?
> Ciao, Concezio.
>
>
> Antonio Petrella wrote:
> > Hi,
> >
> > we also computed a correction factor for the signal/peaking bkg using
> > the entire mx distribution, not a bin by bin.
> >
> > In this case the fit looks better, with respect to the bin by bin one:
> >
> > http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fix129/test_fix129fitresults.eps
> >
> > http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedfitresults.eps
> >
> >
> > cheers,
> > Antonio
>
