Hi,
I have been looking a bit more into the effect reported here by Daniele.
There seems to be a significant jump, mostly a drop in the B0 background
MC, between the selection gam=0/trk=3 and the selection gam=6/trk=6.

The differences between the two selections are :

gam 0 :  energyGam[i] >= 0.08
trk 3 :  goodtrackveryloose + acc


gam 6:  energyGam[i] >= 0.08&& energyGam[i]<4. && lMomGam[i]>0.05 &&
lMomGam[i]<0.5 && s9s25Gam[i]>0.9 && acc;
trk 6 : goodtrackveryloose +  require Dch hits if Pt>200 MeV (note: no
acceptance cut)

No unmatched neutral cluster removal in either selection.

The basic difference is due to the cut on the lateral momentum (between
0.05 and 0.5) and the S9/S25.

I have compared the MC shapes for gam=0,trk=3 (dots) and gam=6,trk=6
(histo) both in
MC
http://www.slac.stanford.edu/~rfaccini/phys/vub/comp_110602B0-03/-comp.html
and in data
http://www.slac.stanford.edu/~rfaccini/phys/vub/comp_110602B0-03data/-comp.html

I would say that the quantities related to the tracks undergo minimal
changes, while the neutral related ones change quite a bit.

We therefore decided to factorize the problems and run only with
trk 6 and gam=5 i.e. the same selection without the Lat cut, which might
be particularly different between data and MC. This turned out to yield,
for the B0
BRBR = 0.0393843 +- 0.0069899(stat) +- 0.00342245(MC stat)
which is to be compared with
BRBR = 0.0274513 +- 0.00629619(stat) +- 0.00355559(MC stat)
in g00 and
BRBR = 0.037327 +- 0.00518964(stat) +- 0.00305673(MC stat)
in g03


It looks like the jump is caused by the other cuts (
energyGam[i]<4. or s9s25Gam[i]>0.9 && acc
which look quite innocuous.

the data MC agreement is in
http://www.slac.stanford.edu/~rfaccini/phys/vub/comp_110602B0-trk7gam5/-comp.html

	comments by voice, since the meeting has started ...
	Ric
P.S. in checking the options I realized that neither the trk=6 nor the
trk=7 option have the tracking acceptance turned on. I then committed a
version of the code with the acceptance on (I do not expect it to be a
dramatic effect, but it was a mistake)

On Sat, 9 Nov 2002, Daniele del Re wrote:

>
> Hi all,
>
>  these are the results fitting the data with the different selections from
> Urs:
>
>  http://www.slac.stanford.edu/~daniele/vub/testsele.html
>
>  I fitted the new and the old MC. I also realized that the selection I
> used to perform all the tests and scans is a bit different from our newest
> selection. I had killTracks=1, killSlowPions=1, doTrackKilling=3 .
>
>  My comments:
>
>  - old-new MC's are the identical as far as the fit result is concerned
>  - Bch results are stable with all the selections
>  - B0 results show large differences between g00 and g01,2,3
>  - MC shapes:
>     * B0 g01 - B0 gdan show a very different shape, do we understand
>       this?
>     * Bch g02- Bch g03 show a very different shape, do we understand
>       this?
>  - data: according to me the three different selections (g01,2,3)
>    change the data very slightly
>
>  My final comment:
>
>  - Bchs look very good. B0 don't. We should understand which is the cut
> that change so much the result from g00 to g01,2,3 for the B0s
>
>
>  Daniele
>
>