Changes to Madspin in MadGraph 2.8.x ?

Asked by Dominik Duda on 2021-01-17

Dear experts,

I am trying to produce some h + jets events with the Feynrule model HC_NLO_X0_UFO-heft with subsequent decay of the Higgs boson into W-bosons using MadSpin. In previous versions of MadGraph I never experienced any problem with this process, but since recent updates in the ATLAS software (or rather with the switch to MadGraph VERSION 2.8.1) I seem to not manage to make the decay

decay x0 > w+ w-

work anymore. MadSpin tells me:

"ZeroResult : No Phase Space. Please check particle masses."

which suggest to me that there is a problem with the fact that one of the W-bosons is supposed to be off-shell. Thus I wanted to ask whether something was changed related to MadSpin that would require some changes to the MadSpin card when using the model HC_NLO_X0_UFO-heft ?

Best regards,
Dominik

Question information

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Last query:
2021-01-17
Last reply:
2021-01-20

Since MadSpin is in the narrow-width approximation, such decay was never supported.

> which suggest to me that there is a problem with the fact that one of the W-bosons is supposed to be off-shell.

I do not see how is it how this is possible to go trough within MadSpin.
(Neither in 2.8.x nor in previous version).
I would strongly suggest to double check what you did in previous version and consider as suspecious (or better just trash) any generation that was done with such syntax (and for such benchmark).

Cheers,

Olivie

> On 17 Jan 2021, at 20:55, Dominik Duda <email address hidden> wrote:
>
> New question #695047 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/695047
>
> Dear experts,
>
> I am trying to produce some h + jets events with the Feynrule model HC_NLO_X0_UFO-heft with subsequent decay of the Higgs boson into W-bosons using MadSpin. In previous versions of MadGraph I never experienced any problem with this process, but since recent updates in the ATLAS software (or rather with the switch to MadGraph VERSION 2.8.1) I seem to not manage to make the decay
>
> decay x0 > w+ w-
>
> work anymore. MadSpin tells me:
>
> "ZeroResult : No Phase Space. Please check particle masses."
>
> which suggest to me that there is a problem with the fact that one of the W-bosons is supposed to be off-shell. Thus I wanted to ask whether something was changed related to MadSpin that would require some changes to the MadSpin card when using the model HC_NLO_X0_UFO-heft ?
>
> Best regards,
> Dominik
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dominik Duda (dduda) said : #2

Hi Olivier,

thanks for the quick reply. I just double-checked the MadSpin card of a sample previously produced in ATLAS and indeed the MadSpin card sets:

set max_weight_ps_point 1000
define l- = e- mu- ta-
define l+ = e+ mu+ ta+
decay x0 > w+ w- > l+ vl l- vl~

Good to know that this is not correct. What would be the recommended way of decaying the
Higgs boson ? Should we do the decay in Pythia instead ?

Best,
Dominik

Hi Dominik,

> decay x0 > w+ w- > l+ vl l- vl~

This syntax is valid (if you have the line "set spinmode=none")
So no issue if you used that one.

while
> decay x0 > w+ w-
is not valid

> Should we do the decay in Pythia instead ?

I guess that Pythia should be as good as MadSpin in this particular case (if not even better).
Indeed the spinmode=none does not have any offshell effect (Pythia might have those) and not spin-correlation between production and decay (this is irrelevant since they are no spin-correlation between production and decay for scalar).

Cheers,

Olivier

> On 18 Jan 2021, at 01:45, Dominik Duda <email address hidden> wrote:
>
> Question #695047 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/695047
>
> Dominik Duda posted a new comment:
> Hi Olivier,
>
> thanks for the quick reply. I just double-checked the MadSpin card of a
> sample previously produced in ATLAS and indeed the MadSpin card sets:
>
> set max_weight_ps_point 1000
> define l- = e- mu- ta-
> define l+ = e+ mu+ ta+
> decay x0 > w+ w- > l+ vl l- vl~
>
> Good to know that this is not correct. What would be the recommended way of decaying the
> Higgs boson ? Should we do the decay in Pythia instead ?
>
> Best,
> Dominik
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dominik Duda (dduda) said : #4

Dear Olivier,

ok sorry my previous messages were stupid. I.e. I did not give you sufficient information. I tried quite a few setups in VERSION 2.8.1 starting from

set spinmode none
decay x0 > w+ w- > l+ vl l- vl~

which gives me an output message:

CRITICAL: The number of event generated is only 1/1200. This typically indicates that you need specify cut on the decay process.
generate 12:16:20 CRITICAL: We strongly suggest that you cancel/discard this run.
generate 12:16:20 CRITICAL: Branching ratio larger than one for 25

the generate + time is coming from the ATLAS software. I also tried x0 > all which gives me mainly decays via X0->gg and X0->tautau but no X0 -> WW nor X0-> ZZ although when setting kSM = 1.0
the Higgs should have SM-like couplings to W and Z in the HC_NLO_X0_UFO-heft model.

I also changed the cut values defined in the runCard (after seeing the problem stated above.

All these problems do not occur in Version 2.7.3, which runs fine with

set spinmode none
decay x0 > w+ w- > l+ vl l- vl~

and gives me an output like:

generate 12:55:01 INFO: generate 1000 decay event for particle x0
generate 12:55:07 INFO: Will use seed 857869765
generate 12:55:34 decaying event number 100 [0.35315990448 s]
generate 12:55:34 decaying event number 200 [0.701221942902 s]
generate 12:55:34 decaying event number 300 [1.0481967926 s]
generate 12:55:34 decaying event number 400 [1.39187288284 s]
generate 12:55:34 decaying event number 500 [1.73956680298 s]
generate 12:55:34 decaying event number 600 [2.08711600304 s]
generate 12:55:34 decaying event number 700 [2.43150281906 s]
generate 12:55:34 decaying event number 800 [2.77896094322 s]
generate 12:55:34 decaying event number 900 [3.12545681 s]

Hence I was wondering whether there have been some changes in 2.8.1 to MadSpin.

Hope this clarifies the situation a bit better.

Best, Dominik

What is the value of the width for the W?
This is the only singularity that I can see in this case.

Cheers,

Olivier

> On 20 Jan 2021, at 14:25, Dominik Duda <email address hidden> wrote:
>
> Question #695047 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/695047
>
> Dominik Duda posted a new comment:
> Dear Olivier,
>
> ok sorry my previous messages were stupid. I.e. I did not give you
> sufficient information. I tried quite a few setups in VERSION 2.8.1
> starting from
>
> set spinmode none
> decay x0 > w+ w- > l+ vl l- vl~
>
> which gives me an output message:
>
> CRITICAL: The number of event generated is only 1/1200. This typically indicates that you need specify cut on the decay process.
> generate 12:16:20 CRITICAL: We strongly suggest that you cancel/discard this run.
> generate 12:16:20 CRITICAL: Branching ratio larger than one for 25
>
> the generate + time is coming from the ATLAS software. I also tried x0 > all which gives me mainly decays via X0->gg and X0->tautau but no X0 -> WW nor X0-> ZZ although when setting kSM = 1.0
> the Higgs should have SM-like couplings to W and Z in the HC_NLO_X0_UFO-heft model.
>
> I also changed the cut values defined in the runCard (after seeing the
> problem stated above.
>
> All these problems do not occur in Version 2.7.3, which runs fine with
>
> set spinmode none
> decay x0 > w+ w- > l+ vl l- vl~
>
> and gives me an output like:
>
> generate 12:55:01 INFO: generate 1000 decay event for particle x0
> generate 12:55:07 INFO: Will use seed 857869765
> generate 12:55:34 decaying event number 100 [0.35315990448 s]
> generate 12:55:34 decaying event number 200 [0.701221942902 s]
> generate 12:55:34 decaying event number 300 [1.0481967926 s]
> generate 12:55:34 decaying event number 400 [1.39187288284 s]
> generate 12:55:34 decaying event number 500 [1.73956680298 s]
> generate 12:55:34 decaying event number 600 [2.08711600304 s]
> generate 12:55:34 decaying event number 700 [2.43150281906 s]
> generate 12:55:34 decaying event number 800 [2.77896094322 s]
> generate 12:55:34 decaying event number 900 [3.12545681 s]
>
> Hence I was wondering whether there have been some changes in 2.8.1 to
> MadSpin.
>
> Hope this clarifies the situation a bit better.
>
> Best, Dominik
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dominik Duda (dduda) said : #6

The width entries from the param card are:

11:51:27 ###################################
11:51:27 ## INFORMATION FOR DECAY
11:51:27 ###################################
11:51:27 DECAY 6 1.491500e+00 # top width
11:51:27 DECAY 23 2.441404e+00 # Z width
11:51:27 DECAY 24 2.047600e+00 # W width
11:51:27 DECAY 25 4.070000e-03 # X0 width

which are identical between 2.8.1 and 2.7.3

Best, Dominik

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