MadGraph5_aMC@NLO

Massive c/b in PS using 5FS

Asked by Nicolas Gutierrez

Dear all,

Is there a setting in MG to add back the masses to the b/c quarks
after the ME calculation in the 5FS?

To explain a bit better please find some example logfiles below
[1] http://www.hep.ucl.ac.uk/~nortiz/log.generate.sm-no_b_mass.b_in_ME.2
[2] http://www.hep.ucl.ac.uk/~nortiz/log.generate.sm-no_b_mass.b_from_gTObbbar.2
Search for "pythia event list" for the most relevant sections.

In [1] a massless b is produced in the hard process, which is good.
However this same b is still massless on the pythia event listing,
which AFAIK means that it is being showered as a massless parton.
In contrast, in [2] where there no b in the hard process, but during the PS
a gluon splits in b-bbar, both massive.
This does not seem good to me.

What I had expected is that somewhere between after ME before PS
the massless b-4V in [1] would be re-calculated.

Thanks,
       Nicolas

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Typically, this computation will be done internally by the Parton-Shower.

Cheers,

Olivier

PS: Otherwise CMS devellop a code addmasses.py.
(which is shipped with MG: Template/LO/bin/internal/addmasses.py)
one of the main point is to add the masses before the parton-shower.
Note that the plan is to remove that file in future version.

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