Pythia not properly initialized for processes involving new particles.

Asked by Jason Hiroshi Arakawa on 2020-01-21

Dear Reader,

I am new to Madgraph and Pythia, so any help would be appreciated. I am trying to generate events involving new particles in Madgraph, and want to use Pythia to shower. I am using MG5 version 2.6.3.2, and Pythia8235.

I am able to generate the events in Madgraph fine from what I can tell (the .lhe file looks fine, and does complete). The problem is when I try to shower them. If the process is a simple SM process, the showering/hadronization works, and it completes. However, as soon as I introduce a process with new particles, it isn't able to shower the events. If I look at the output of Pythia, it gives the error:

PYTHIA Abort from Pythia::next: not properly initialized so cannot generate events

and therefore does not write anything to the output files. To give more specifics on what I've done, the model that I'm trying to look at is a new scalar, phi0, that has electroweak and Higgs interactions. Some of the processes I've tried to generate are:

generate phi0 phi0 > w+ w- (with and without the Higgs channel)
generate phi0 phi0 > u u~ (through a Higgs channel)
generate phi0 phi0 > h h

All of which give the same abort error when I try to shower. Again, however, if I run,

generate p p > u u~

Pythia works fine and showers. It seemed like to me that it could be on the side of the model file that was generated with FeynRules, but it's unclear to me why Madgraph would work and Pythia won't initialize if it is.

A full outline of what I've entered into MG5 is:

import model RealScalar_WIMP_UFO/
generate phi0 phi0 > w+ w-
output Pythia_test
launch

Then I simply did 10 events with a mass for phi0 of 150 GeV.

I tell Pythia to shower the events after Madgraph generates them, but it never completes.

So, if I go to the event and run ./run_shower.sh, the output is:

 *------------------------------------------------------------------------------------*
 | |
 | *------------------------------------------------------------------------------* |
 | | | |
 | | | |
 | | PPP Y Y TTTTT H H III A Welcome to the Lund Monte Carlo! | |
 | | P P Y Y T H H I A A This is PYTHIA version 8.235 | |
 | | PPP Y T HHHHH I AAAAA Last date of change: 27 Mar 2018 | |
 | | P Y T H H I A A | |
 | | P Y T H H III A A Now is 21 Jan 2020 at 13:08:21 | |
 | | | |
 | | Christian Bierlich; Department of Astronomy and Theoretical Physics, | |
 | | Lund University, Solvegatan 14A, SE-223 62 Lund, Sweden; | |
 | | e-mail: <email address hidden> | |
 | | Nishita Desai; Laboratoire Charles Coulomb (L2C), | |
 | | CNRS-Universite de Montpellier, 34090 Montpellier, France; | |
 | | e-mail: <email address hidden> | |
 | | Nadine Fischer; School of Physics, | |
 | | Monash University, PO Box 27, 3800 Melbourne, Australia; | |
 | | e-mail: <email address hidden> | |
 | | Ilkka Helenius; Institute for Theoretical Physics, | |
 | | Tuebingen University, Auf der Morgenstelle 14, 72076 Tuebingen, Germany; | |
 | | e-mail: <email address hidden> | |
 | | Philip Ilten; School of Physics and Astronomy, | |
 | | University of Birmingham, Birmingham, B152 2TT, UK; | |
 | | e-mail: <email address hidden> | |
 | | Leif Lonnblad; Department of Astronomy and Theoretical Physics, | |
 | | Lund University, Solvegatan 14A, SE-223 62 Lund, Sweden; | |
 | | e-mail: <email address hidden> | |
 | | Stephen Mrenna; Computing Division, Simulations Group, | |
 | | Fermi National Accelerator Laboratory, MS 234, Batavia, IL 60510, USA; | |
 | | e-mail: <email address hidden> | |
 | | Stefan Prestel; Theoretical Physics Department, | |
 | | Fermi National Accelerator Laboratory, MS 106, Batavia, IL 60510, USA; | |
 | | e-mail: <email address hidden> | |
 | | Christine O. Rasmussen; Department of Astronomy and Theoretical Physics, | |
 | | Lund University, Solvegatan 14A, SE-223 62 Lund, Sweden; | |
 | | e-mail: <email address hidden> | |
 | | Torbjorn Sjostrand; Department of Astronomy and Theoretical Physics, | |
 | | Lund University, Solvegatan 14A, SE-223 62 Lund, Sweden; | |
 | | e-mail: <email address hidden> | |
 | | Peter Skands; School of Physics, | |
 | | Monash University, PO Box 27, 3800 Melbourne, Australia; | |
 | | e-mail: <email address hidden> | |
 | | | |
 | | The main program reference is 'An Introduction to PYTHIA 8.2', | |
 | | T. Sjostrand et al, Comput. Phys. Commun. 191 (2015) 159 | |
 | | [arXiv:1410.3012 [hep-ph]] | |
 | | | |
 | | The main physics reference is the 'PYTHIA 6.4 Physics and Manual', | |
 | | T. Sjostrand, S. Mrenna and P. Skands, JHEP05 (2006) 026 [hep-ph/0603175] | |
 | | | |
 | | An archive of program versions and documentation is found on the web: | |
 | | http://www.thep.lu.se/Pythia | |
 | | | |
 | | This program is released under the GNU General Public Licence version 2. | |
 | | Please respect the MCnet Guidelines for Event Generator Authors and Users. | |
 | | | |
 | | Disclaimer: this program comes without any guarantees. | |
 | | Beware of errors and use common sense when interpreting results. | |
 | | | |
 | | Copyright (C) 2018 Torbjorn Sjostrand | |
 | | | |
 | | | |
 | *------------------------------------------------------------------------------* |
 | |
 *------------------------------------------------------------------------------------*

 *----------------------- SusyLesHouches SUSY/BSM Interface ------------------------*
 | Last Change 12 Apr 2017 - P. Skands
 | Parsing: unweighted_events.lhe.gz
 | (SLHA::readFile) line 414 - storing non-SLHA(2) block: ckmblock
 | (SLHA::readFile) line 419 - storing non-SLHA(2) block: frblock
 | (SLHA::readFile) line 454 - storing non-SLHA(2) block: yukawa
 | (SLHA::readFile) line 488 - storing QNUMBERS for id = 9000005 phi0
 | (SLHA::readFile) line 496 - storing QNUMBERS for id = 9000006 phi+
 *------------------------------------------------------------------------------------*
 PYTHIA Info from SLHAinterface::initSLHA: No MODSEL found, keeping internal SUSY switched off
 PYTHIA Info from SLHAinterface::initSLHA: importing MASS entries for id = {25,9000005,9000006}
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring MASS entries for id = {1,2,3,4,5,6,11,12,13,14,15,16,21,22,23,24} (SLHA:keepSM. Use id > 1000000 for new particles)
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring DECAY tables for id = {6,23,24,1,2,3,4,5,11,12,13,14,15,16,21,22} (SLHA:keepSM. Use id > 1000000 for new particles)
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring empty DECAY tables for id = {25} (total width provided but no Branching Ratios)
 PYTHIA Error in Pythia::init: cannot handle this beam combination
 PYTHIA Abort from Pythia::init: checkBeams initialization failed
Counting events in input LHEF, please wait.
Found 10 events in input LHEF.

Start generating events
 *----------------------- SusyLesHouches SUSY/BSM Interface ------------------------*
 | Last Change 12 Apr 2017 - P. Skands
 | Parsing: unweighted_events.lhe.gz
 | (SLHA::readFile) line 414 - storing non-SLHA(2) block: ckmblock
 | (SLHA::readFile) line 419 - storing non-SLHA(2) block: frblock
 | (SLHA::readFile) line 454 - storing non-SLHA(2) block: yukawa
 | (SLHA::readFile) line 488 - storing QNUMBERS for id = 9000005 phi0
 | (SLHA::readFile) line 496 - storing QNUMBERS for id = 9000006 phi+
 *------------------------------------------------------------------------------------*
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring QNUMBERS for id = 9000005 (already exists)
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring QNUMBERS for id = 9000006 (already exists)
 PYTHIA Info from SLHAinterface::initSLHA: importing MASS entries for id = {25,9000005,9000006}
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring MASS entries for id = {1,2,3,4,5,6,11,12,13,14,15,16,21,22,23,24} (SLHA:keepSM. Use id > 1000000 for new particles)
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring DECAY tables for id = {6,23,24,1,2,3,4,5,11,12,13,14,15,16,21,22} (SLHA:keepSM. Use id > 1000000 for new particles)
 PYTHIA Warning in SLHAinterface::initSLHA: ignoring empty DECAY tables for id = {25} (total width provided but no Branching Ratios)
 PYTHIA Abort from Pythia::next: not properly initialized so cannot generate events

Thank you very much, and please let me know what other information I can provide!
Jason Arakawa

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Jason Hiroshi Arakawa
Solved:
2020-01-21
Last query:
2020-01-21
Last reply:
2020-01-21

Hi,

I'm not a Pythia expert.

Pythia is by default using QCD shower however your processes might not have QCD particles at all which requires some specific handling in the pythia_card to have them to be handle correctly (I can see plenty parameter of PY8 to change from default and I probably miss a couple of them.)

The first question here is what do you want/expect. If you are interested in indirect detection, you should use MadDM and not madgraph. That tool (plugin of MG5aMC) have the correct interface/setup to py8 to have the correct shower for that specific case.

Cheers,

Olivier

Hi Olivier,

Thank you for getting back to me. Yes, I am interested in indirect detection. I installed MadDM, and it solved my problem!

Thanks!
Jason