Code review comment for lp:~maddevelopers/mg5amcnlo/NLO_decay_process

Hi guys,

Could we finish this review soon such that we can release 2.3.3?

I take a look and it works nicely. Great work.
Here is a couple of superficial comment/question:
(I did not look at the code since I'm not a reviewer)

1) I tried:
generate t > b all all [QCD]

and I have the following warning:
WARNING: Process: t > b g/gh/gh~/d/u/s/c/d~/u~/s~/c~/a/ve/vm/vt/e-/mu-/ve~/vm~/vt~/e+/mu+/b/t/b~/t~/z/w+/h/w-/ta-/ta+ g/gh/gh~/d/u/s/c/d~/u~/s~/c~/a/ve/vm/vt/e-/mu-/ve~/vm~/vt~/e+/mu+/b/t/b~/t~/z/w+/h/w-/ta-/ta+ [ all = QCD ] can have real emission processes which are not finite.
To avoid this, please use multiparticles when generating the process and be sure to include all the following particles in the multiparticle definition:
 g, c, s, u, d, d~, u~, s~, c~

This should not be raised right?

Finally it crashed with:

Command "launch auto " interrupted with error:
IOError : [Errno 2] No such file or directory: '/Users/omatt/Documents/eclipse/NLO_decay_process/topwidth/SubProcesses/P0_t_tbbx/channels.txt'
Please report this bug on https://bugs.launchpad.net/madgraph5
More information is found in '/Users/omatt/Documents/eclipse/NLO_decay_process/topwidth/run_01_tag_1_debug.log'.
Please attach this file to your report.

This should be very simple to prevent.

2) I tried
generate w+ > all all [QCD]
and it also crashes:

Command "generate w+ > all all [QCD]" interrupted with error:
InvalidCmd : All loop diagrams discarded by user selection.
 Consider using a tree-level generation or relaxing the coupling order constraints.
Please report this bug on https://bugs.launchpad.net/madgraph5
More information is found in 'MG5_debug'.
Please attach this file to your report.

3) I tried
generate t > w+ b [QCD]
then I see as output:

(Partial) decay width: 1.347e+00 +- 8.9e-03 GeV
Ren. and fac. scale uncertainty: +1.2% -1.5%

One small remark here, "factorization variation" is irrelevant here and can be remove from the log [but ok we can keep it do not hurt]

then I re-run with fix (renormalisation) scale computation (at 90GeV) and get
(Partial) decay width: 1.343e+00 +- 9.2e-03 GeV
Clearly my scale choice is not consider.

This is confusion (at minima) and should either works or at least raise a warning that we do not support that (but should be easy to handle).
I would propose that the default "dynamical" scale is the mass of the decaying particle.
and that at least static scale works.

4) [This should not be implemented now but I want to start the discussion].
For the moment the "only" output is a partial width/plot. It will be useful to have a param_card as output with updated information (that's typically the point of computing the width).
Concerning the BR, this is obviously less clear @NLO, but I would propose that we use the "proton"
pdg code for the branching ratio to avoid problem with the massless quark flavor. (this can be discussed with pythia/herwig author)

Cheers,

Olivier