Very small particle momenta when using converter_card.tcl to go from Pythia 8 .hep to .root

[Kayla]

Hello. I am currently using MadGraph 5 and Pythia 8.210 to simulate vector-mediated dark matter models. I simulate a Z boson decaying leptonically as well as a dark matter pair in pp collisions. I am trying to use Pythia to simulate the underlying event, after which I obtain a .hep file.

I would like to make some validation plots at this stage. I did a bit of digging and found that I can use Delphes to convert from .hep to .root, using converter_card.tcl.

However, when I do DelphesHepMC converter_card.tcl events.hep events.root, the particle momenta are drastically different in the .root file compared to the .hep file. For example, after converting, I don't get any leptons with Pt > 1 GeV. They all have values on the order of 10^-130, whereas I can see in the .hep file that they have completely reasonable values, on the order of ~10 GeV.

It seems that the converter card is doing something strange to the particles. I am using the latest version of Delphes 3.2.0. Any insight is appreciated! Thank you.

[Pavel Demin]

From your description it's not very clear what files your are converting. DelphesHepMC should be used with HepMC files that normally have extension .hepmc. DelphesSTDHEP should be used with STDHEP files that have extension .hep.

If you are using DelphesHepMC with .hep files then DelphesHepMC should crash with an error message.

[Kayla]

Thank you for your response. I realize my mistake between .hepmc and .hep files. Pythia 8.210 is actually outputting a .hepmc file, but I had given it the wrong extension. There is a HepMC header in the Pythia output file.

My question is still relevant then. When I try to convert with DelphesHepMC, the particle momenta are extremely small compared to inside the .hepmc file.

[Michele Selvaggi]

Hi,

could you please attach a small (~1k events) hepmc sample that you find troublesome, so we can have a look what's going on?

Thanks
Michele

[Kayla]

I have attached a .hepmc file with 100 events (1k events was around 180 MB, too large to upload). I also attached the .root file after converting with the Delphes converter card. I downloaded the converter card from here:
​https://github.com/delphes/delphes/blob/master/cards/converter_card.tcl

Please let me know if you need more information. Thank you again.

[Michele Selvaggi]

Hi,

sorry for the late answer. By roughly comparing the first event of the hepmc file with the Delphes output I don't find any difference. Could you point out more precisely to some particle (and event number) which has different momenta in the two formats?

Thanks,
Michele