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 4vec and the photon 4vec,
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/vubnosf/ejhill/ana_issues/bremrecov/pstarcomp.eps
http://www.slac.stanford.edu/BFROOT/www/Physics/Analysis/AWG/InclusiveSL/vubnosf/ejhill/ana_issues/bremrecov/mxhadfitcomp.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/vubnosf/ejhill/ana_issues/bremrecov/pstarcomp_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 1015% depending on the mode.
>  the removal of brem photon changes and improves significantly the
> reconstruction of the inclusive X mass (mxhadfit)
>
> Daniele
