Hoi Ric,

 >  - what happens if you require the already suggested cut Ndch>0 if pt<200
 > MeV? Does the effect disappear? I guess slide 3 should tell me something
 > but I do not know what you are plotting.

You  mean loopers? No.  Most of  the loopers  are SVT-only  pieces not
linked to  the main track.  If a track  exits the tracking  volume, it
will start a new track.

> slide 3

page 2? Delta  phi as calculated between close  candidates in delta pT
and delta  theta. 'Close' means 200 MeV  for pT and 0.2  rad for theta
(and v.v.  0.3  in delta phi when displaying  delta theta).  These are
just loose cuts for displaying,  the matching cuts for looper searches
are tighter (and at the moment  'by eye'). In the left most column you
see conversion (the  peak at delta phi = zero)  and loopers (the peaks
at delta  phi =  +/-pi).  For  the theta plots,  only the  loopers are
shown. All  the plots  on page 2  (as indicated  at the bottom  of the
page, not in acroread) are on data.

Ghost tracks are  tracks with pT > 200 MeV, same  sign, same phi, same
theta.  Same distributions  as for loopers on preceding  page. I don't
yet understand the  phi distribution in data. It  looks different from
MC.

 >  - what do you mean efficiency is low? I cannot understand which cut you
 > are suggesting to apply and what is its efficiency.

I don't say  it's low. All I say  is that there is a  resiudal bump in
data at  theta = 90 degree which  is more significant in  data than in
MC. 

 >  - I do not understand how does the material you show quantify the issue
 > on Qtot. Which is the fraction of events where the loopers have an impact on
 > the charge reconstruction? How well is it reproduced between data and MC?
 > Applying an ad hoc selection how well can we do in removing the problem?

Remember, it's not a final result  ...  Loopers have an impact on Qtot
whenever the 'No. of Duplicates' on page 6 is odd. The total number of
events  processed in data  was 596330,  the plot  (top left)  seems to
indicate something like 25-30k tracks where one remaining os-looper is
killed.

Note  that in  the distributions  I  have not  disentangled BRECO  and
recoil.   Loopers  are also  contained  in  the  BRECO tracks  (cannot
quantify at the moment). This might be an entirely different story.

I admit that  I have a conceptual problem with  the combination of the
Qtot cut and the tracking features  alluded to in my posting. The gain
of having  the statistical error on Vub  go from (say) 10%  to 9% (the
10% improvement  is based on a pure  MC study) but having  to prove to
ourselves  satisfactorily  that  the  MC  does  a  good  (enough)  job
describing problems (not features) in tracking seems marginal.


Cheers,
--U.