Difference: SingleTopPolarization (104 vs. 105)

Revision 1052013-09-30 - AndreaGiammanco

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META TOPICPARENT name="AndreaGiammanco"

Single Top Polarization analysis

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  • Resurrect cut-based cross-check analysis (based on C instead of eta_j'?) [Andres, Steffen]
  • Separate measurements for top and antitop (in addition, not as replacement to the global result.)
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From the ARC, Sep.26:

     ---> the difference of event selection between the electron and muon channels are inducing some strong differences between the 2 channels (MT vs MET) for example the tight MET cut on electron induce high sensitivity to some systematics like JER. For publication, we would like suggest to harmonize the selection between the two channels, and possibly using cut on MT for both channels.

     --->  There is some lack of statistics in some systematic samples => These statistical fluctuations seem to affect more the electron channel, as its  selection efficiency is lower. For publication, we would like to suggest to produce more MC events where it is needed (hoping there is enough computing resources).

    ---> while a conservative approach was followed by the authors, we would like to see some more investigation on the mis-modeling of the costheta* distribution by madgraph. For publication, we would like to suggest to work on better understanding of the mis-modeling of the costheta* distribution by, possibly, make details MC studies/comparisons (comparisons with other generators, investigate effects of matching, propagations of spin information etc...). 

    ---> Concerning TopFit, the correlations of measurements in the limit calculation are neglected. This is a feature of the program (analysts have no hand on it). This assumption, which is done also in W-helicity measurement by ATLAS and CMS if I understood perperly,  is made clear in the text. For publication, we would like to see with the authors and Aguilar if correlations can be introduced in a decent amount of time.

    ---> We would also suggest to investigate the reliability of jet-ID up to |eta|<4.5 and possibly (re-)optimize the "root-mean-square particle-jets deltaR" selection.

    ---> The usage of a the CSV tagger should help to remove more backgrounds with a possible increase the signal statistic. The determination of the best working point might be needed.

    ---> We understood that the BDT selection would benefit from a re-optimization.

    ---> As discussed (and proposed) by the authors, the QCD background normalization in the second background fit should be fixed to the estimation of the first background fit.

    --->
In the combination of the top polarization, it might help to investigate better the correlations between the systematics.

    --->
Some synchronization with the W helicity in single-top could be investigated.

From Jeremy, Sep.27:

That would be great if you
could at least redo the nice analysis from Nadjieh. In particular,
instead of inverting the isolation cut on electron isolation >0.1, one
could try to investigate how the mTW bias is behaving by bins of
isolation, like   0.1 < iso < X. There might be some intervals with smaller
bias.

Also, the fact that Nadjieh is looking at the 2jets0tag category make
the sample enriched in jet reconstructed as electrons, while there could
be a significant effect of btagging for the fraction of non-prompt
electron from heavy hadron decays. The bias can be smaller in the signal
region.

One could also investigate a combination of a loose MET cut and a
tighter mWT cut, which would have to be optimized.
 

Talks in CMS meetings

 
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