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H+: intermediate mass region
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Minutes from the H+ intermediate mass treatment
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https://indico.cern.ch/event/352630/
* the problem: H+ production is pp->tt; t->bH+ dominated
for mH+ < 160 GeV and pp->tH+ X dominated for mH+ > 200 GeV.
In the intermediate mass region we have to consider
these two processes and their interference.
* There are two sub-problems in this procedure:
- how to calculate the cross sections for H+ production
in mH+: 160-200 GeV
- what MC to use
* For the cross section calculation Martin Flechl suggested
that a time-scale realistic proposal would be to devise
some empirical function to combine the individual cross sections
sigma(pp->tt; t->bH+) and sigma(pp->tH+ X) as a function of
mH+ with a very approximate method to subtract the interference
(since its contribution is negative). This could be done by
using the cross section tables shown in Weydert et al arXiv:0912.3430
(MC@LNO, so 5FS). The uncertainty of this method has to be studied
carefully. A point that has to be discussed is what to do with
analysis cuts on the number of b-tags and the pT of b-jets, since
this affect the size of the interference term.
Michael Spira suggested that with the method which the separate
cross sections are combined without any explicit matrix element
calculation of the interference the uncertainties would go at
the 20-30% level. A rough estimation of the uncertainty can be
done by comparing the different contributions in the plot
shown in slide 4 of Martin's presentation (from arXiv:hep-ph/0312286).
It is not quite clear from this plot that the uncertainties will
end up to 30%, but this has to be studied carefully.
In general, more feedback from the theory community is needed on
the idea of adding the separate cross section contributions
empirically.
* For the MC Michael Spira suggested that there is a full
NLO calculation with MG5_aMC@NLO or Powheg in the 4FS. It is recommended
to contact Fabio Maltoni et al + Powheg authors and discuss the details.
Michael suggested not to consider 5FS at all for the time being
neither to consider any uncertainty due to that.
Action Items:
- receive feedback from WG3 for the proposed idea of cross section
combination
- receive feedback from MG5_aMC@NLO team for the NLO MC generation.
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