problem with generating b b > A > h z /a [QCD]

Hi,

The error message that I get in your case is:

 Error in set_shower_scale_noshape:
 not enough QCD partons in process 0

That part of the code complains that you do not have any QCD particles particles and going to NLO QCD does not therefore make any sense. The point here is that the b quark is massive in 2HDM_NLO and therefore the associated radiation are not singular.
Using your process definition (with b in initial state) is actually not fully consistent since the pdf assumes massless b quark.

So the way to fix this is to either do the computation at LO, or set the b-mass to zero (at the model level):
The way to set the mass to zero is explained here:
https://answers.launchpad.net/mg5amcnlo/+faq/2312

However, just setting the b-mass to zero is not enough for doing the computation at NLO accuracy.
Since the b is massless it has now the same singularity as the other massless quark and in order to have NLO accuracy you can not distinguish b jet from other flavor.
So in top you need to change your process definition to
(with the default p definition which will include b if you applied the method explained above)
generate p p > h3 > h1 z /a [QCD]

Cheers,

Olivier

https://answers.launchpad.net/mg5amcnlo/+faq/2312
And you indeed have an inconsistency with your process (and different part of the code are handling that differently making any result meaningless).

1) initial state particles need to be massless to use lhapdf. (and this is quite important at NLO).

Thank you Olivier that is solved my question