mmll cut for massless four lepton final states

Asked by Lailin Xu on 2020-02-19

Hi,

I understand that mmll cut would not work for massless four lepton final states, like "p p > l+ l- l+ l-". But I'm just wondering
if you have any suggestions to work around the problem.
Is it possible to simply apply the mll cut to all same-flavor opposite-sign lepton pairs, regardless of the lepton mass?

Thanks,
Lailin

Question information

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Last query:
2020-02-19
Last reply:
2020-02-23

Hi,

Did you try this:

set group_subprocesses False
generate p p > l+ l- l+ l-
output
launch
set mmll 50

The option "group_subprocesses" deactivate a lot of the optimization including those forbidding to use the mmll cut in this case. Actually in term of optimisation, this goes back to the speed of MadGraph4 and this actually impressive how slow this computation is.

Cheers,

Olivier

> On 19 Feb 2020, at 15:37, Lailin Xu <email address hidden> wrote:
>
> New question #688870 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/688870
>
> Hi,
>
>
> I understand that mmll cut would not work for massless four lepton final states, like "p p > l+ l- l+ l-". But I'm just wondering
> if you have any suggestions to work around the problem.
> Is it possible to simply apply the mll cut to all same-flavor opposite-sign lepton pairs, regardless of the lepton mass?
>
> Thanks,
> Lailin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Lailin Xu (xlltoade) said : #2

Hi Olivier,

Thanks for your quick response! I have tried this, but it crashed.
You can find the log file at:
https://cernbox.cern.ch/index.php/s/A7OefsszVhtRSfg
Could you take a look?

Thanks,
Lailin

Can you try with the latest version of the code,
if this still does not work, try by setting dynamical_scale_choice to 3 in the run_card

Cheers,

Olivier

> On 19 Feb 2020, at 16:22, Lailin Xu <email address hidden> wrote:
>
> Question #688870 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/688870
>
> Status: Answered => Open
>
> Lailin Xu is still having a problem:
> Hi Olivier,
>
> Thanks for your quick response! I have tried this, but it crashed.
> You can find the log file at:
> https://cernbox.cern.ch/index.php/s/A7OefsszVhtRSfg
> Could you take a look?
>
> Thanks,
> Lailin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Lailin Xu (xlltoade) said : #4

Hi Olivier,

OK, I'll try the latest code.
But I just tried the same code I used, but with dynamical_scale_choice of 3, and it seemed to be working, with a sensible cross section.
But I noticed some warnings like:

10:49:50 INFO: Idle: 0, Running: 14, Completed: 320 [ 1m 1s ]
10:49:55 Note: The following floating-point exceptions are signalling: IEEE_UNDERFLOW_FLAG IEEE_DENORMAL
10:49:56 Note: The following floating-point exceptions are signalling: IEEE_UNDERFLOW_FLAG IEEE_DENORMAL

Is this something to worry about?

I'll let you know how the newest code works with dynamical_scale_choice of -1.

Thanks,
Lailin

Lailin Xu (xlltoade) said : #5

Hi Olivier,

I tried v2.7.0. With dynamical_scale_choice of -1 , I got the same error as for v2.6.

At line 671 of file cluster.f
Fortran runtime error: Index '0' of dimension 1 of array 'imap' below lower bound of 1
rm: cannot remove ‘results.dat’: No such file or directory
ERROR DETECTED

But it worked with dynamical_scale_choice of 3.

Thanks,
Lailin

Can I ask you to give me details on the model/process that you are using?
I will then reproduce the issue localy and should be able to fix it with the default dynamical scale

Cheers,

Olivier

Lailin Xu (xlltoade) said : #7

Hi Olivier,

Sure, the model is taken from: https://feynrules.irmp.ucl.ac.be/wiki/SMEFT
I put a copy below:
https://cernbox.cern.ch/index.php/s/0zSfAqdgojIGHeg

My proc_card can be found at the same place: proc_card_SMEFT_4l.dat.

So you should be easy to reproduce the problem I saw.

Thanks a lot for looking into this issue!

Lailin

Ok,

I have investigate it and it should be related (in some way) to this message:

CRITICAL: Model with non QCD emission of gluon (found 14 of those).
  This type of model is not fully supported within MG5aMC.
  Restriction on LO dynamical scale and MLM matching/merging can occur for some processes.
  Use such features with care.

So I can not fixed it without a full rewritting of the CKKW dynamical scale to be more BSM friendly (which I will not do)

Cheers and thanks,

Olivier

Lailin Xu (xlltoade) said : #9

Hi Olivier,

Many thanks for looking into this!
I have a couple of points:
1. Indeed I saw this message when running 2.6.6. But I also tried 2.6.5 with the exact setting, and did not see it.
So this might be a new feature added after 2.6.5?

2. Related to that message, so your suggestion is to use dynamic scale of 3, not the default one? Do you have any suggestions?

Thanks,
Lailin

Hi,

> 1. Indeed I saw this message when running 2.6.6. But I also tried 2.6.5 with the exact setting, and did not see it.
> So this might be a new feature added after 2.6.5?

The issue was much older than that but we were not putting any warning/automated crash related to that before 2.6.6.

> 2. Related to that message, so your suggestion is to use dynamic scale
> of 3, not the default one? Do you have any suggestions?

Yes using 3 should be the way to more forward.

Cheers,

Olivier

> On 23 Feb 2020, at 10:37, Lailin Xu <email address hidden> wrote:
>
> Question #688870 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/688870
>
> Lailin Xu posted a new comment:
> Hi Olivier,
>
> Many thanks for looking into this!
> I have a couple of points:
> 1. Indeed I saw this message when running 2.6.6. But I also tried 2.6.5 with the exact setting, and did not see it.
> So this might be a new feature added after 2.6.5?
>
> 2. Related to that message, so your suggestion is to use dynamic scale
> of 3, not the default one? Do you have any suggestions?
>
> Thanks,
> Lailin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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