Photons not written in the LHE file

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 (?)
>
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