Z offshell problem in syntax p p > z z l+ l- / h

Olivier Mattelaer suggests this article as an answer to your question:
FAQ #2173: “Intermediate Boson missing from events in LHE output file”.

Hi Oliver,

Thanks, let me explain myself in detail.
Using the following syntax:
p p > z z l+ l- / h

I am making selections on the two pairs of opposite sign same flavour leptons. The first pair is chosen in such a way that invariant mass is close to the nominal Z mass (Z1). The second pair is remaining leptons 3 and 4(Z2). Now my expectation is I should have Z1 with some spread around 91 GeV. but instead I get 0 or 91( Sharp values). The attachment shows the plot for that. Similarly the Z2 is expected to have fairly large off-shell component. Instead I see a on shell Z2 with some values peaking at zero. The plots showing the results are attached.

Let me know if there is some problem understanding this.

Cheers,
Bilal

> On 26 Sep 2017, at 20:13, Olivier Mattelaer <email address hidden> wrote:
>
> Your question #658677 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> Status: Open => Answered
>
> Related FAQ set to:
> Intermediate Boson missing from events in LHE output file
> https://answers.launchpad.net/mg5amcnlo/+faq/2173
>
> Olivier Mattelaer proposed the following answer:
> Olivier Mattelaer suggests this article as an answer to your question:
> FAQ #2173: “Intermediate Boson missing from events in LHE output file”.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/mg5amcnlo/+question/658677/+confirm?answer_id=0
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> You received this question notification because you asked the question.

Dear Bilal,

Sorry I'm confused, you only have one pair of lepton with your syntax.
So I do not understand your question.

Cheers,

Olivier

So, both the Z’s in the syntax are allowed to decay according to the BF. So there should be events with four of more leptons in the final state. No?

Bilal
> On 27 Sep 2017, at 20:47, Olivier Mattelaer <email address hidden> wrote:
>
> Your question #658677 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> Status: Open => Needs information
>
> Olivier Mattelaer requested more information:
> Dear Bilal,
>
> Sorry I'm confused, you only have one pair of lepton with your syntax.
> So I do not understand your question.
>
> Cheers,
>
> Olivier
>
> --
> To answer this request for more information, you can either reply to
> this email or enter your reply at the following page:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> You received this question notification because you asked the question.

Hi,

Ok, how do you handle such decay? Did you let the parton-shower doing it? Or do you use something more reliable?

So how do you select the events? Did you request events with 4 lepton exactly? What did you do if you have more/less lepton in your final state? Since this is at parton level, how do you define your lepton ? (isolation/cut/...)

What are the cut that you applied at parton-level? The fact that you have a huge component at zero (I did not see the plot since attachment did not go trough) indicates that you might have fail to set the cut needed to remove the photon divergences.

Cheers,

Olivier

Hi,

Ok, how do you handle such decay? Did you let the parton-shower doing it? Or do you use something more reliable?

So how do you select the events? Did you request events with 4 lepton exactly? What did you do if you have more/less lepton in your final state? Since this is at parton level, how do you define your lepton ? (isolation/cut/...)

What are the cut that you applied at parton-level? The fact that you have a huge component at zero (I did not see the plot since attachment did not go trough) indicates that you might have fail to set the cut needed to remove the photon divergences.

Cheers,

Olivier

Hi,

So I let parton-shower do the decay. And I am only selecting exactly four lepton in the final state since I am interested in looking for this type of background in my H->ZZ-4l selection. Since this is generator level there is no conditions of the lepton isolation/cut etc etc. For the zero component there could be some some test done to remove that part, but the real problem is just a delta function at 91. I select for the four leptons in the final state, with the first OS pair invariant mass closest to the PDG Z as Z1 and other two as Z2. Now there could be events with leptons less or more than four lepton but I discard such events. The only selection in the run card on the invariant mass of mll > 4 to avoid low mass resonances . But except that there is no other specific cut of leptons.

Cheers,
BIlal
> On 28 Sep 2017, at 09:53, Olivier Mattelaer <email address hidden> wrote:
>
> Your question #658677 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> Olivier Mattelaer proposed the following answer:
> Hi,
>
> Ok, how do you handle such decay? Did you let the parton-shower doing
> it? Or do you use something more reliable?
>
> So how do you select the events? Did you request events with 4 lepton
> exactly? What did you do if you have more/less lepton in your final
> state? Since this is at parton level, how do you define your lepton ?
> (isolation/cut/...)
>
> What are the cut that you applied at parton-level? The fact that you
> have a huge component at zero (I did not see the plot since attachment
> did not go trough) indicates that you might have fail to set the cut
> needed to remove the photon divergences.
>
> Cheers,
>
> Olivier
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/mg5amcnlo/+question/658677/+confirm?answer_id=5
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> You received this question notification because you asked the question.

Hi,

So I let parton-shower do the decay. And I am only selecting exactly four lepton in the final state since I am interested in looking for this type of background in my H->ZZ-4l selection. Since this is generator level there is no conditions of the lepton isolation/cut etc etc. For the zero component there could be some some test done to remove that part, but the real problem is just a delta function at 91. I select for the four leptons in the final state, with the first OS pair invariant mass closest to the PDG Z as Z1 and other two as Z2. Now there could be events with leptons less or more than four lepton but I discard such events. The only selection in the run card on the invariant mass of mll > 4 to avoid low mass resonances . But except that there is no other specific cut of leptons.

Cheers,
BIlal
> On 28 Sep 2017, at 09:53, Olivier Mattelaer <email address hidden> wrote:
>
> Your question #658677 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> Olivier Mattelaer proposed the following answer:
> Hi,
>
> Ok, how do you handle such decay? Did you let the parton-shower doing
> it? Or do you use something more reliable?
>
> So how do you select the events? Did you request events with 4 lepton
> exactly? What did you do if you have more/less lepton in your final
> state? Since this is at parton level, how do you define your lepton ?
> (isolation/cut/...)
>
> What are the cut that you applied at parton-level? The fact that you
> have a huge component at zero (I did not see the plot since attachment
> did not go trough) indicates that you might have fail to set the cut
> needed to remove the photon divergences.
>
> Cheers,
>
> Olivier
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/mg5amcnlo/+question/658677/+confirm?answer_id=5
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/658677
>
> You received this question notification because you asked the question.

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