# Param_card in MadSpin

Dear experts,

I am generating some samples like generate p p > h2 > t t~, and then use MadSpin to define the decay of top quark. I use a param_card, whice has set the width of h2 and t, in MadEvent. And MadSpin caculate another parem_card because the previous one did not contain the branch of t, and in this card the width of h2 is difference with the previous one. I am not sure which width is used.

I would appreciate your help. Thank you!

Yizhou

## Question information

- Language:
- English Edit question

- Status:
- Solved

- Assignee:
- No assignee Edit question

- Solved by:
- Yizhou Cai

- Solved:
- 2021-03-04

- Last query:
- 2021-03-04

- Last reply:
- 2021-03-04

So the one used is the one computed by MadSpin, since it needs to be consistent with the BR information.

If that one does not match your previous one, you will get a warning (as you have observe I guess).

To avoid that, you have to specify not only the full-width but also the BR information in the original param_card and madspin will then use that information.

Cheers,

Olivier

> On 3 Mar 2021, at 15:05, Yizhou Cai <email address hidden> wrote:

>

> New question #695837 on MadGraph5_aMC@NLO:

> https:/

>

> Dear experts,

>

> I am generating some samples like generate p p > h2 > t t~, and then use MadSpin to define the decay of top quark. I use a param_card, whice has set the width of h2 and t, in MadEvent. And MadSpin caculate another parem_card because the previous one did not contain the branch of t, and in this card the width of h2 is difference with the previous one. I am not sure which width is used.

>

> I would appreciate your help. Thank you!

>

> Yizhou

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

Yizhou Cai (yzcai) said : | #2 |

I just got the following lines of output:

INFO: We need to recalculate the branching fractions for t~,w-,w+,t

INFO: using the FeynRules formula present in the model (arXiv:1402.1178)

So h2 > t t~ process use the latter card, even if the process was not defined in MadSpin?

If you have in your madspin_card a line

decay A

and that in the param_card has not the BR for particle A

then all particle with "decay" have their width re-computed.

Cheers,

Olivier

> On 4 Mar 2021, at 03:05, Yizhou Cai <email address hidden> wrote:

>

> Question #695837 on MadGraph5_aMC@NLO changed:

> https:/

>

> Yizhou Cai posted a new comment:

> I just got the following lines of output:

>

> INFO: We need to recalculate the branching fractions for t~,w-,w+,t

> INFO: using the FeynRules formula present in the model (arXiv:1402.1178)

>

> So h2 > t t~ process use the latter card, even if the process was not

> defined in MadSpin?

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

Yizhou Cai (yzcai) said : | #4 |

No, I don't have this line. There is just decay t and w in Madspin card.

Cheers,

Yizhou

So in that case, your width for h2 is not recomputed and should have the same value for the two cards.

> On 4 Mar 2021, at 08:30, Yizhou Cai <email address hidden> wrote:

>

> Question #695837 on MadGraph5_aMC@NLO changed:

> https:/

>

> Yizhou Cai posted a new comment:

> No, I don't have this line. There is just decay t and w in Madspin card.

>

> Cheers,

> Yizhou

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

Yizhou Cai (yzcai) said : | #6 |

I think so, but it recaculated the width of h2 in some of my previous work. I'm not sure now if I did it wrong...

Thanks a lot for reply.