Custom Cuts - Accessing Mother ID of the nexternal particles

Hi Ryan,

I'm a bit worry about such kind of cut because:

1)if you use the "mother" information for the cut, then your cut are potentially diagram dependent which is not physical at all. This doesn't sounds a correct definition for a cut.

2) in optimize_mode (the default) the diagram from different subprocesses are merged for the integration and therefore some cuts might not be valid if such merging
is not in agreement with your cut (you then need to use the non optimized mode via the command "set group_subprocesses False". For checking W this shouldn't be a problem.

> I'm trying to make sense of the 'iforest( , )' tag, but I don't see what information this carries.

That's the way to go if you want to have access to the mother.
Let's take a simple example:
g g> t t~
the configs.inc is the following:
C Diagram 1
      DATA MAPCONFIG(1)/1/
      DATA (IFOREST(I,-1,1),I=1,2)/4,3/
      DATA (SPROP(I,-1,1),I=1,1)/21/
      DATA TPRID(-1,1)/0/
C Diagram 2
      DATA MAPCONFIG(2)/2/
      DATA (IFOREST(I,-1,2),I=1,2)/1,3/
      DATA TPRID(-1,2)/6/
      DATA (SPROP(I,-1,2),I=1,1)/0/
      DATA (IFOREST(I,-2,2),I=1,2)/-1,4/
C Diagram 3
      DATA MAPCONFIG(3)/3/
      DATA (IFOREST(I,-1,3),I=1,2)/1,4/
      DATA TPRID(-1,3)/6/
      DATA (SPROP(I,-1,3),I=1,1)/0/
      DATA (IFOREST(I,-2,3),I=1,2)/-1,3/
C Number of configs
      DATA MAPCONFIG(0)/3/

let's read it:
C Diagram 1
      DATA MAPCONFIG(1)/1/
we are creating configuration 1 (which here correspond to diagram 1):
      DATA (IFOREST(I,-1,1),I=1,2)/4,3/
the particle 3 and 4 join to create the particle -1
      DATA (SPROP(I,-1,1),I=1,1)/21/
The particle -1 is in S-channel and this is gluon (pdg=21)
      DATA TPRID(-1,1)/0/
The particle -1 is not in t-channel (no pdg associated)

The rest of the diagram is not present (i.e. how it link to initial particle, this is uniquely define in practise)

C Diagram 2
      DATA MAPCONFIG(2)/2/
we are creating configuration 2 (which here correspond to diagram 2):
      DATA (IFOREST(I,-1,2),I=1,2)/1,3/
particle 1 and 3 combine to create -1
      DATA TPRID(-1,2)/6/
particle -1 is in T channel and is a top (pdg=6)
      DATA (SPROP(I,-1,2),I=1,1)/0/
particle -1 is not in S-channel
      DATA (IFOREST(I,-2,2),I=1,2)/-1,4/
particle -1 and 4 combine to create particles -2 (which is in fact particle 2, so this particle has two identification)

…

So you need to combine iforest with SPROP and TPRID.

Cheers,

Olivier

On Nov 20, 2013, at 11:06 PM, Ryan <email address hidden> wrote:

> New question #239560 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/239560
>
> Any help here would be superbly appreciated…
>
> I'm implementing a custom invariant WW mass cut for VBS processes and TTbar. The cut is easy to do for VBS, because the W daughters are always in the same index position.
>
> BUT, for the background TTbar and WJets events, the daughters are not always in the same position. I need a general way of accessing the mothers. I'm trying to make sense of the 'iforest( , )' tag, but I don't see what information this carries.
>
> If there's a simple way of accessing the mother MC ID for any particle within the 'nexternal' particles, that would make this very easy. Is there such a method?
>
> -Ryan DeC
>
> --
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