amc@nlo showered with herwig 6 problem

[Giancarlo Panizzo]

Dear Delphes team,

I'm trying to produce showered events with aMC@NLO + HERWIG 6 (default option). The final hep file can be read by Delphes with no problems, but all brunches are empty except for the Event and Particle ones. The Event.weight seems to have the correct sign, but multiplied by a factor 262.97537 (the fraction of negative weight events is the same given by aMC@NLO output). The Particle kinematical variables seem more or less meaningful on average, but the information on particle masses and on M1,M2,D1,D2 are not stored.
Running Delphes on the lhe file produced before hadronisation does work correctly.

Giancarlo

[Pavel Demin]

Dear Giancarlo,

Could you, please provide an example of your hep file?

Pavel

[Giancarlo Panizzo]

The original file was too heavy, I've generated a second one with only 100 events. I've uploaded the lhe parton events too. My Delphes version in 3.0.7, coming with aMC@NLO. The code to feed Delphes was

DelphesSTDHEP examples/delphes_card_ATLAS.tcl delphes_output.root events_HERWIG6_0.hep

Giancarlo

[Pavel Demin]

Dear Giancarlo,

Thank you for the files.

I've fixed a bug in the function that decodes STDHEP4 blocks (STDHEP + event weight).

Now particle status and mother/daughter indexes are correctly read and stored.

I've also checked that both Delphes and MCFIO/STDHEP read exactly the same values.

Here is a version with fixed STDHEP reader:

​​http://cp3.irmp.ucl.ac.be/downloads/Delphes-3.0.9.pre1.tar.gz

Could you, please check if this version works for you?

I've also noticed the following problems with your STDHEP file:

• The event weights stored in this file are indeed multiplied by some large value. I get the same values with both Delphes and MCFIO/STDHEP. For example, here are the weights for the first three events:

  264.212
  264.212
  264.212
  

• Some particles with status=1 have unphysical (nan or inf) vertex positions. Again I get the same values with both Delphes and MCFIO/STDHEP. For example, here is a list of such particles from the first event:

  number PID   X   Y   Z     Px        Py        Pz
  61     14   nan nan nan  91.1621  -95.9792 -264.129
  62    -13   nan nan nan  23.2651  -17.7621   -8.16779
  73    -12   nan nan nan -67.5527   14.8692   60.7669
  74     11   nan nan nan   6.20367  13.9842  -16.8727
  

Regards,

Pavel

[Pavel Demin]

I've just found that Herwig++ before 2.1.1 produced nan for some vertex positions:

​https://herwig.hepforge.org/trac/ticket/123

​http://herwig.hepforge.org/oldversions.html

Is it possible that aMC@NLO somehow escapes the GenericWidthGenerator tests?

[Giancarlo Panizzo]

The new version works well, I confirm the problem with nan in average 15 particles per event, that's more or less 3% of particles on average.

I've seen your reply in the initial MG5 question #229096, I will post there the same comment, I think the discussion for Delphes for what concerns my problem can be closed here :)

Thanks a lot

Giancarlo

[Giancarlo Panizzo]

Forgot the numbers I gave you, they were about Warnings on 0 transverse momentum, that may not be related to the vertex problem.

Thanks again

Giancarlo

[Pavel Demin]

The fixed STDHEP reader is in Delphes 3.0.9 now.