Hi-

To follow up on Daniele's posting ...
(this is all found on my page on brem recovery linked from ISL->vubnosf->...)

As stated in the meeting - i explored 2 different ways of identifying brem 
photons - the opening angle between the lepton 4-vec and the photon 4-vec, 
and the difference in theta, phi origin between the lepton and photon.

I compared my 2 ways and Daniele's way and here are the pstar and Mx plots:
http://www.slac.stanford.edu/BFROOT/www/Physics/Analysis/AWG/InclusiveSL/vub-nosf/ejhill/ana_issues/bremrecov/pstar-comp.eps
http://www.slac.stanford.edu/BFROOT/www/Physics/Analysis/AWG/InclusiveSL/vub-nosf/ejhill/ana_issues/bremrecov/mxhadfit-comp.eps

The 3 methods are pretty similar here, and agree with what Daniele posted.

A much more interesting plot is this one-> I made a plot of the pstar for ONLY 
the events where brem was recovered - and compared it to those corresponding 
events before brem recovery.
http://www.slac.stanford.edu/BFROOT/www/Physics/Analysis/AWG/InclusiveSL/vub-nosf/ejhill/ana_issues/bremrecov/pstar-comp_bremrecov.eps
You can see very clearly in this plot the positive effect of applying a brem 
recovery.

I also checked on the efficiency of making the selection for recovery

For a sample of signal (brevubmix)->

**TRUTH is determined if the photon is:
  1. a daughter of a B (apparently they are written in the truth block as 
B->Xlvg, not B->Xlv; l->lg)
  2. the photon's mother B is the same mother B of the electron (i.e. - the 
electron and photon are from the same B)

If i cut on opening angle between e, gam:
1084 leptons are selected as having brem photon(s)
-->1004 of those are TRUE brem leptons ( 80 are mistakenly selected)
401 TRUE brem leptons are missed by the selection
N(selected)/N(True) = 0.77

If i cut on delta theta/phi seperately:
1064 leptons are selected as having brem photons
--> 993 of those are TRUE brem leptons (71 are mistakenly selected)
412 TRUE brem leptonss are missed by the selection
N(selected)/N(True) = 0.76

Following DDR's cutting scheme:
1072 leptons are selected as having brem photons
--> 985 of those are TRUE brem leptons (87 are mistakenly selected)
420 TRUE brem leptons are missed by the selection
N(selected)/N(True) = 0.76

Cheers,
Ed


On Friday 09 April 2004 04:39 pm, Daniele del Re allegedly wrote:
> Hi all,
>
>  when studying momentum resolution in lepton ID I realized that
> that bremsstrahlung for electrons can introduce large biases in
> p* efficiency and resolution. It can also affect the mm2 resolution
> and finally it produces large biases in the inclusive Mx reconstruction.
>
>  I the past we always neglected this point.
>
>  A couple of examples. Here is the p* resolution comparison
> between e and mu:
>
> http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/resoelemu.eps
>
>  that shows that the effect is large. And this is mm2 for pi0lnu:
>
> http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/mm2pi0elemu.eps
>
> (for the inclusive calculation of mm2 the effect is smaller because the
> brem photon is included in the X system and then recoil has it).
>
>  I implemented a brem recovery algorithm that is very similar to the one
> in Beta. Code is in VubAnalysis (in util.icc).
>  It is based on two variables
>
>  - Delta(theta): it is the difference between the theta of the brem photon
>    and the electron one. They should be the same within resolutions.
>
>  - DD = (Phi(gamma)-Phi(e production))/Phi(e EMC)-Phi(e production)): here
>    I am requesting that the phi of the gamma is in between the phi of the
>    electron at the EMC and the phi at the origin. I used this ratio
>    (instead of a simple cut on Phi(gamma)-Phi(e production) as in Beta)
>    because numerator and denominator are somehow proportional.
>
>  Here the distributions for electrons
>  Delta(theta) (for -0.3<DD<0.6)
>  http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/Deltatheta.eps
>
>  DD (for -0.04<Delta(theta)<0.04)
>  http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/DD.eps
>
>  I finally select brem photon with these cuts
>  -0.04<Delta(theta)<0.04 && -0.3<DD<0.6
>  and I redefined the electron p4 as p4+p4(brem photon). Moreover the
> brem photons are removed from the good photon list (goodPhoton[i] = 0)
>
>
>  The following plots are a comparison with and without the correction:
>
>  resolution in p*:
>  http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/resoelecorr.eps
>
>  mm2 for pi0lnu:
>  http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/mm2pi0elecorr.eps
>
>  inclusive mm2
>  http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/mm2elecorr.eps
>  (small effect as expected, see above, mostly due to gain in p* cut
>   efficiency)
>
>  inclusive fitted X mass (mxhadfit)
> 
> http://www.slac.stanford.edu/~daniele/exclvub/bremstudy/mxhadfitelecorr.eps
>
>
>  Conclusions:
>  - brem recovery improves largely the resolution in p* and the efficiency
>    of p* cut (~+5%)
>  - it improves mm2 resolution in exclusive calculation of mm2. total mm2
>    cut efficiency increase by 10-15% depending on the mode.
>  - the removal of brem photon changes and improves significantly the
>    reconstruction of the inclusive X mass (mxhadfit)
>
>  Daniele