Muon Displacement Not Simulated Properly

Asked by Wei Shi on 2019-05-16

Dear MG5 experts,

I was recently checking the simulation of the events from the LHE file [1] produced from MadGraph5. In each event, we have two light boson (PDG ID =3000022) each decays to a pair of oppositely charged muons. We also manually added lifetime (using a python script and change the lifetime column) for the boson in the LHE events so that it can travel some distance before decaying to muons. In such cases, the muons are expected to be displaced from the interaction point/ beam line.

We simulate the events all the way to the event reconstruction in the CMS detector. From the CMS event display in [2], I can see the GEN level muons are displaced as expected (The white curves in the main RhoPhi view). But things are a bit more complicated for the reconstructed muons (red curves). In this specific event, we see two close-by muons reconstructed for the same GEN displaced muon. One of the two reconstructed muons is displaced as we expected, the other is prompt (easier to see in the zoomin plot in [2]). But both has almost equal pT, eta and phi. More often, in many other events where GEN muon is displaced, the reconstructed muon is not displaced at all.

We also went back to the beginning of simulation chain for the specific event in [2], where we found there are duplicate close-by simulation hits in the muon detector for the same GEN displaced muon[3]( red dots indicate simulated hits in the CMS DT muon detector; purple dots indicate simulated hits in the CMS RPC muon detecor). This result in the downstream reconstructed close-by muons.

So it seems the generator level muon displacement information is not well simulated/propagated. In some events, it does get passed to simulation, but the simulation also seems to simulate another prompt version of the displaced muon. I wonder if you could help take a look at the LHE file [1] and see if it's possible we introduced some mistake inside.

Cheers,
Wei

[1]
Boson (PDG id=3000022) mass 5GeV, average lifetime cTau=50mm:
https://www.dropbox.com/s/6vjq3kdxlms2xj8/MSSMD_10_5_50.lhe?dl=0

[2]
https://www.dropbox.com/s/bxg1dos9zxwozl2/07-15-07-28341-Event49_RECO.png?dl=0

Zoomin:
https://www.dropbox.com/s/2tgb99yq8a6eefi/07-15-07-45408-Event49_RECO_zoomin.png?dl=0

[3]
https://www.dropbox.com/s/x54p7vvu8obe5b6/07-15-07-30061-Event49_GENSIM_LowerPair.png?dl=0
https://www.dropbox.com/s/9q9u0dbfz1rogp4/07-15-07-60335-Event49_GENSIM_UpperPair.png?dl=0

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
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Last query:
2019-05-16
Last reply:
2019-05-18

Do I understand correctly that you are not using MG5aMC to set the lifetime information inside the lhe file?

In that case why do you contact us?

Cheers,

Olivier

Wei Shi (weishi10141993) said : #2

Hi Olivier,

We couldn't use the option in MG5aMC for madspin as said earlier in this thread (#9) : https://answers.launchpad.net/mg5amcnlo/+question/668537

Here I just wonder if there is anything that might cause this issue from the perspective of MG5 generated LHE file.

Cheers,
Wei

I look at your lhe file and do not spot anything really suspicious about it.
Now some line does not start with space anymore. I heard that CMS lhe parser is quite sensitive to any change (but this is just rumor)
Now you should rather discuss this with the code using that information
(cheking first the information after the parton-shower)

Cheers,

Olivier

> On 16 May 2019, at 23:42, Wei Shi <email address hidden> wrote:
>
> Question #680885 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/680885
>
> Wei Shi posted a new comment:
> Hi Olivier,
>
> We couldn't use the option in MG5aMC for madspin as said earlier in this
> thread (#9) : https://answers.launchpad.net/mg5amcnlo/+question/668537
>
> Here I just wonder if there is anything that might cause this issue from
> the perspective of MG5 generated LHE file.
>
> Cheers,
> Wei
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Wei Shi (weishi10141993) said : #4

Hi Olivier,

Could you be more specific regarding this:

(checking first the information after the parton-shower)?

Cheers,
Wei

My suggestion is to check how that information propagate to understand what is going out. But I can not be more specific

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________________________________
From: <email address hidden> on behalf of Wei Shi <email address hidden>
Sent: Saturday, May 18, 2019 12:32 AM
To: Olivier Mattelaer
Subject: Re: [Question #680885]: Muon Displacement Not Simulated Properly

Question #680885 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/680885

Wei Shi posted a new comment:
Hi Olivier,

Could you be more specific regarding this:

(checking first the information after the parton-shower)?

Cheers,
Wei

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