Generating root file of tHq with mg5

Asked by Jazmine Jefferson on 2017-11-30

I am new to madgraph and I am attempting to generate a root file for a tHq process with h > w+ w-, w+ > mu vm, w- > mu vm~. Any process I have tried to employ from reading other tHq related questions have not worked. The run throws an error when I attempt to launch the decay process.

For each run, I set it up by:

define p = g u c d s u~ c~ d~ s~ b b~
define j = p
I have tried:

generate p p > t h j
add process p p > t~ h j
edit pythia run card file for decay

generate p p > t h j $$ w+ w-
output
turn on madspin and edit madspin card file for decay

generate p p > t h j, h > w+ w-, w
>invalid process

Any help would be appreciated, thanks

Question information

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MadGraph5_aMC@NLO Edit question
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Last query:
2017-11-30
Last reply:
2017-11-30

Hi,

I would do the following (syntax valid since 2.6.1, for older version see below)

> import model sm-no_b_mass
> generate p p > t h j
> output
> launch
> madspin=none
> decay h > w+ w- > mu+ mu- vm vm~
 # to run as ./bin/mg5_aMC PATH_TO_THE_FILE
So the idea here is to use madspin in the special spinmode=None (i.e. no spin-correlation between production and decay and no off shell effects)
to handle the Higgs decay.

I would not use the normal “sm” model since in that model the b quark is massive and this is not fully consistent to have a massive quark in the initial state.

Note that you can also do the following (i.e. adding matching/merging):
> generate p p > t h j
> add process p p > t~ h j

but then you have to check that you are using a sensitive matching scale to check that you correctly remove the double counting in the above definition.
(by default we use MLM but a quite low scale which might be too small for your process)

Concerning this:
> generate p p > t h j $$ w+ w-

This is also a valid syntax that I typically discouraged since it can sometimes return not physical results (by breaking gauge invariance)
The idea of this syntax is to forbid all the diagram where a W+/W- is in s-channel.
You have a softer version of the same idea:
> generate p p > t h j $ w+ w-

where you only forbid the w+/w- to be onshell (up to X times the width, X is a parameter of the run_card (bwcutoff) and is default is 15)

Cheers,

Olivier

PS: for version below 2.6.1, you can do (a more ugly syntax)

> import model sm-no_b_mass
> generate p p > t h j
> output
> launch
> madspin==ON
> add madspin --after_line=banner set spinmode=none
> decay h > w+ w- > mu+ mu- vm vm~

you can obviously edit the madspin_card by hand instead of scripting the modification as pointed above

> On Nov 30, 2017, at 16:26, Jazmine Jefferson <email address hidden> wrote:
>
> New question #661291 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/661291
>
> I am new to madgraph and I am attempting to generate a root file for a tHq process with h > w+ w-, w+ > mu vm, w- > mu vm~. Any process I have tried to employ from reading other tHq related questions have not worked. The run throws an error when I attempt to launch the decay process.
>
> For each run, I set it up by:
>
> define p = g u c d s u~ c~ d~ s~ b b~
> define j = p
> I have tried:
>
> generate p p > t h j
> add process p p > t~ h j
> edit pythia run card file for decay
>
> generate p p > t h j $$ w+ w-
> output
> turn on madspin and edit madspin card file for decay
>
> generate p p > t h j, h > w+ w-, w
>> invalid process
>
> Any help would be appreciated, thanks
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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