Photons not written in the LHE file

Asked by Alexandros Marantis on 2021-06-07

Dear Olivier,
I'm generating the following processes

generate p p > j j mu+ mu- mu+ mu- QCD=0
add process p p > j j e+ e- mu+ mu- QCD=0
add process p p > j j e+ e- e+ e- QCD=0

in a single sample in order to study the qgc contribution in the zzjj channel.

After that, I categorize the decay channels by counting the intermediate state bosons which are written in the LHE file and I end up with a list like the following (for 22k events):

----- Number of events per decay channel -----
 pp->ZZ->eeeejj , events: 3240
 pp->ZZ->mmmmjj , events: 3358
 pp->ZZ->eemmjj , events: 8179
 Sum of the 4e, 4m, 2e2m channels: 14777
 pp->ZZ->lllljj , events: 14777
 pp->ZW->lllljj , events: 254
 pp->ZH->lllljj , events: 580
 pp->WW->lllljj , events: 0
 pp->WH->lllljj , events: 16
 pp->ZZW->lllljj , events: 2008
 pp->ZZH->lllljj , events: 499
 pp->ZZZ->lllljj , events: 2209
 pp->ZWW->lllljj , events: 0
 pp->WWW->lllljj , events: 0
 pp->ZWH->lllljj , events: 96
 pp->ZZZW->lllljj , events: 0
 pp->ZZZH->lllljj , events: 33
 pp->ZZWH->lllljj , events: 24
 pp->Z->lllljj , events: 1348
 pp->W->lllljj , events: 9
 pp->H->lllljj , events: 92
 pp->lllljj with no intermediate state , events: 55
 Sum of the above channels: 22000
---------------------------------------------

My question is about the photons, which are not written in the LHE file. While the feynman diagrams including photons are present in the diagram list, I don't see any event with intermediate photons.
I tried to play with the bwcutoff, changing it from 15.0 to 100.0 and then to a very big number (1000000), but nothing changes.
My other photon-related cuts are:
  0.0 = pta ! minimum pt for the photons
  -1.0 = ptamax ! maximum pt for the photons
  0.0 = ea ! minimum E for the photons
  2.5 = etaa ! max rap for the photons
  0.0 = etaamin ! min rap for the photons
  0.0 = draa ! min distance between gammas
  0.4 = dral ! min distance between gamma and lepton
  -1.0 = draamax ! max distance between gammas
  0.0 = mmaa ! min invariant mass of gamma gamma pair
  0.4 = r0gamma ! Radius of isolation code

Is there any other parameter which affects the "visibility" of the photons in the LHE file?

Thanks a lot,
Alexandros

ps In the above list with the intermediate states, the last entry is "4ljj with no intermediate state". Maybe this is the channel with the (off-shell) photons decaying to leptons (?)

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Solved by:
Olivier Mattelaer
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Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said :
#1

Hi,

Only onshell particles are included within the file.
Since the photon can not be on shell it can not be written.

This is particularly important since they are large Z/photon interference above the Z peak and therefore in that region it is impossible to tell if a contribution is a Z or a photon.
It is technically both.

Additionally you can have t-channel diagram where such particle does not fit within the lhef format (which makes sense since they are not onshell)

Cheers,

Olivier

PS: using bwcutoff as large as 100 can lead to various issue starting with bias distribution within the Parton-shower.

> On 7 Jun 2021, at 17:30, Alexandros Marantis <email address hidden> wrote:
>
> New question #697441 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/697441
>
> Dear Olivier,
> I'm generating the following processes
>
> generate p p > j j mu+ mu- mu+ mu- QCD=0
> add process p p > j j e+ e- mu+ mu- QCD=0
> add process p p > j j e+ e- e+ e- QCD=0
>
> in a single sample in order to study the qgc contribution in the zzjj channel.
>
> After that, I categorize the decay channels by counting the intermediate state bosons which are written in the LHE file and I end up with a list like the following (for 22k events):
>
> ----- Number of events per decay channel -----
> pp->ZZ->eeeejj , events: 3240
> pp->ZZ->mmmmjj , events: 3358
> pp->ZZ->eemmjj , events: 8179
> Sum of the 4e, 4m, 2e2m channels: 14777
> pp->ZZ->lllljj , events: 14777
> pp->ZW->lllljj , events: 254
> pp->ZH->lllljj , events: 580
> pp->WW->lllljj , events: 0
> pp->WH->lllljj , events: 16
> pp->ZZW->lllljj , events: 2008
> pp->ZZH->lllljj , events: 499
> pp->ZZZ->lllljj , events: 2209
> pp->ZWW->lllljj , events: 0
> pp->WWW->lllljj , events: 0
> pp->ZWH->lllljj , events: 96
> pp->ZZZW->lllljj , events: 0
> pp->ZZZH->lllljj , events: 33
> pp->ZZWH->lllljj , events: 24
> pp->Z->lllljj , events: 1348
> pp->W->lllljj , events: 9
> pp->H->lllljj , events: 92
> pp->lllljj with no intermediate state , events: 55
> Sum of the above channels: 22000
> ---------------------------------------------
>
> My question is about the photons, which are not written in the LHE file. While the feynman diagrams including photons are present in the diagram list, I don't see any event with intermediate photons.
> I tried to play with the bwcutoff, changing it from 15.0 to 100.0 and then to a very big number (1000000), but nothing changes.
> My other photon-related cuts are:
> 0.0 = pta ! minimum pt for the photons
> -1.0 = ptamax ! maximum pt for the photons
> 0.0 = ea ! minimum E for the photons
> 2.5 = etaa ! max rap for the photons
> 0.0 = etaamin ! min rap for the photons
> 0.0 = draa ! min distance between gammas
> 0.4 = dral ! min distance between gamma and lepton
> -1.0 = draamax ! max distance between gammas
> 0.0 = mmaa ! min invariant mass of gamma gamma pair
> 0.4 = r0gamma ! Radius of isolation code
>
> Is there any other parameter which affects the "visibility" of the photons in the LHE file?
>
> Thanks a lot,
> Alexandros
>
> ps In the above list with the intermediate states, the last entry is "4ljj with no intermediate state". Maybe this is the channel with the (off-shell) photons decaying to leptons (?)
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Alexandros Marantis (amaranti) said :
#2

Thanks Olivier Mattelaer, that solved my question.