Pythia8 aborts, with e+e- whizard, parton+hadronLevel failed

Asked by Aram Apyan on 2021-05-03

Hi,

I am trying to generate e+e- -> 4 fermion (2l + 2q) collision events (*) with Whizard. When I try to shower the events with Pythia8 I get errors and after couple of hundred events it aborts (**).

     11 Abort from Pythia::next: parton+hadronLevel failed; giving up |
 | 110 Error in MiniStringFragmentation::fragment: no 1- or 2-body state found above mass threshold |
 | 110 Error in Pythia::next: hadronLevel failed; try again

My setup works for the other background and signal samples (for example 4 lepton background) and it only fails for this 2l+2q sample. I am not quite sure if I should ask this question to Pythia8 authors but wanted to check if this has been seen here before?

Thank you,

Aram

(*)
alias q = u:d
alias Q = U:D
alias nu = n1:n2:n3
alias Nu = N1:N2:N3
alias lep1 = e1:e2:e3
alias lep2 = E1:E2:E3
process ee4lepton = e1, E1 => (e2, E2, q, Q) + (e2, E2, c, C) + (e2, E2, b, B) + (e2, E2, s, S)
cuts = any M > 20 GeV [e2,E2] and all M > 0.5 [q:s:c:b,Q:S:C:B]
beams = e1, E1 => isr # include the isr
sqrts = 91.1876 GeV
n_events = 100000
sample_format = lhef
simulate (ee4lepton)

(**)
*------- PYTHIA Process Initialization --------------------------*
 | |
 | We collide e- with e+ at a CM energy of 9.119e+01 GeV |
 | |
 |------------------------------------------------------------------|
 | | |
 | Subprocess Code | Estimated |
 | | max (mb) |
 | | |
 |------------------------------------------------------------------|
 | | |
 | Les Houches User Process(es) 9999 | 8.554e-10 |
 | |
 *------- End PYTHIA Process Initialization -----------------------*

 *------- PYTHIA Flag + Mode + Parm + Word + FVec + MVec + PVec + WVec Settings (changes only) ------------------*
 | |
 | Name | Now | Default Min Max |
 | | | |
 | Beams:eCM | 91.18760 | 14000.000 10.00000 |
 | Beams:frameType | 4 | 1 1 5 |
 | Beams:LHEF | /tmp/arapyan/ee4lepton.lhe | void |
 | Init:showChangedParticleData | off | on |
 | Main:numberOfEvents | 100000 | 1000 0 |
 | Next:numberCount | 100 | 1000 0 |
 | Next:numberShowEvent | 0 | 1 0 |
 | StringFlav:etaSup | 0.63000 | 0.60000 0.0 1.00000 |
 | StringFlav:mesonBvector | 3.00000 | 2.20000 0.0 3.00000 |
 | StringFlav:mesonCvector | 1.06000 | 0.88000 0.0 3.00000 |
 | StringFlav:mesonSvector | 0.72500 | 0.55000 0.0 3.00000 |
 | StringFlav:mesonUDvector | 0.62000 | 0.50000 0.0 3.00000 |
 | StringFlav:popcornSpair | 0.50000 | 0.90000 0.0 1.00000 |
 | StringFlav:probQQ1toQQ0 | 0.0270000 | 0.0275000 0.0 1.00000 |
 | StringFlav:probQQtoQ | 0.0900000 | 0.0810000 0.0 1.00000 |
 | StringFlav:probSQtoQQ | 1.00000 | 0.91500 0.0 1.00000 |
 | StringFlav:probStoUD | 0.19000 | 0.21700 0.0 1.00000 |
 | StringPT:sigma | 0.30400 | 0.33500 0.0 1.00000 |
 | StringZ:aExtraDiquark | 0.50000 | 0.97000 0.0 2.00000 |
 | StringZ:aLund | 0.30000 | 0.68000 0.0 2.00000 |
 | StringZ:bLund | 0.80000 | 0.98000 0.20000 2.00000 |
 | StringZ:rFactB | 0.67000 | 0.85500 0.0 2.00000 |
 | StringZ:rFactC | 1.00000 | 1.32000 0.0 2.00000 |
 | TimeShower:alphaSvalue | 0.13830 | 0.13650 0.0600000 0.25000 |
 | TimeShower:pTmin | 0.40000 | 0.50000 0.10000 2.00000 |
 | TimeShower:pTminChgQ | 0.40000 | 0.50000 0.10000 2.00000 |
 | Tune:ee | 3 | 7 -1 7 |
 | |
 *------- End PYTHIA Flag + Mode + Parm + Word + FVec + MVec + PVec + WVec Settings -----------------------------*

 -------- LHA initialization information ------------

  beam kind energy pdfgrp pdfset
     A 11 45.594 -1 -1
     B -11 45.594 -1 -1

  Event weighting strategy = 3

  Processes, with strategy-dependent cross section info
  number xsec (pb) xerr (pb) xmax (pb)
       1 8.5544e-01 1.9719e-03 1.0000e+00

 -------- End LHA initialization information --------

 -------- LHA event information and listing ----------------------------------------------------------------------

    process = 1 weight = 1.0000e+00 scale = 9.1188e+01 (GeV)
                        alpha_em = -1.0000e+00 alpha_strong = 1.1780e-01

    Participating Particles
    no id stat mothers colours p_x p_y p_z e m tau spin
     1 11 -1 0 0 0 0 0.000 0.000 45.594 45.594 0.001 0.000 9.000
     2 -11 -1 0 0 0 0 0.000 0.000 -45.594 45.594 0.001 0.000 9.000
     3 13 1 1 2 0 0 4.120 -6.785 15.466 17.385 0.106 0.000 9.000
     4 -13 1 1 2 0 0 -15.927 21.479 -36.500 45.247 0.106 0.000 9.000
     5 2 1 1 2 501 0 5.307 -9.363 10.057 14.730 0.000 0.000 9.000
     6 -2 1 1 2 0 501 6.500 -5.331 10.977 13.826 0.000 0.000 9.000

 -------- End LHA event information and listing ------------------------------------------------------------------

 -------- PYTHIA Info Listing ----------------------------------------

 Beam A: id = 11, pz = 4.559e+01, e = 4.559e+01, m = 5.110e-04.
 Beam B: id = -11, pz = -4.559e+01, e = 4.559e+01, m = 5.110e-04.

 In 1: id = 11, x = 1.000e+00, pdf = 0.000e+00 at Q2 = 8.315e+03.
 In 2: id = -11, x = 1.000e+00, pdf = 0.000e+00 at same Q2.

 Process Les Houches User Process(es) with code 9999 is 2 -> 4.
 Subprocess user process 1 with code 1 is 2 -> 4.
     alphaEM = 7.818e-03, alphaS = 1.178e-01 at Q2 = 8.315e+03.

 Impact parameter b = 0.000e+00 gives enhancement factor = 1.000e+00.
 Max pT scale for MPI = 9.119e+01, ISR = 9.119e+01, FSR = 9.119e+01.
 Number of MPI = 1, ISR = 0, FSRproc = 4, FSRreson = 0.

 -------- End PYTHIA Info Listing ------------------------------------

 -------- PYTHIA Event Listing (hard process) -----------------------------------------------------------------------------------

    no id name status mothers daughters colours p_x p_y p_z e m
     0 90 (system) -11 0 0 0 0 0 0 0.000 0.000 0.000 91.188 91.188
     1 11 (e-) -12 0 0 3 0 0 0 0.000 0.000 45.594 45.594 0.001
     2 -11 (e+) -12 0 0 4 0 0 0 0.000 0.000 -45.594 45.594 0.001
     3 11 (e-) -21 1 0 5 8 0 0 0.000 0.000 45.594 45.594 0.000
     4 -11 (e+) -21 2 0 5 8 0 0 0.000 0.000 -45.594 45.594 0.000
     5 13 mu- 23 3 4 0 0 0 0 4.120 -6.785 15.466 17.385 0.106
     6 -13 mu+ 23 3 4 0 0 0 0 -15.927 21.479 -36.500 45.247 0.106
     7 2 u 23 3 4 0 0 501 0 5.307 -9.363 10.057 14.730 0.000
     8 -2 ubar 23 3 4 0 0 0 501 6.500 -5.331 10.977 13.826 0.000
                                   Charge sum: 0.000 Momentum sum: -0.000 -0.000 0.000 91.188 91.188

 -------- End PYTHIA Event Listing -----------------------------------------------------------------------------------------------
 PYTHIA Error in MiniStringFragmentation::fragment: no 1- or 2-body state found above mass threshold
 PYTHIA Error in Pythia::next: hadronLevel failed; try again
 PYTHIA Abort from Pythia::next: parton+hadronLevel failed; giving up
** 99 events processed
 Pythia::next(): 100 events have been generated
Event generation aborted prematurely, owing to error!
** 114 events processed

 *------- PYTHIA Event and Cross Section Statistics -------------------------------------------------------------*
 | |
 | Subprocess Code | Number of events | sigma +- delta |
 | | Tried Selected Accepted | (estimated) (mb) |
 | | | |
 |-----------------------------------------------------------------------------------------------------------------|
 | | | |
 | Les Houches User Process(es) 9999 | 115 115 104 | 7.811e-10 2.376e-11 |
 | ... whereof user classification code 1 | 115 115 104 | |
 | | | |
 | sum | 115 115 104 | 7.811e-10 2.376e-11 |
 | |
 *------- End PYTHIA Event and Cross Section Statistics ----------------------------------------------------------*

 *------- PYTHIA Error and Warning Messages Statistics ----------------------------------------------------------*
 | |
 | times message |
 | |
 | 11 Abort from Pythia::next: parton+hadronLevel failed; giving up |
 | 110 Error in MiniStringFragmentation::fragment: no 1- or 2-body state found above mass threshold |
 | 110 Error in Pythia::next: hadronLevel failed; try again |
 | 1 Warning in JetMatchingMadgraph:init: Madgraph merging parameters not found |
 | 1 Warning in JetMatchingMadgraph:init: No alpsfact |
 | 1 Warning in JetMatchingMadgraph:init: No ickkw |
 | 1 Warning in JetMatchingMadgraph:init: No maxjetflavor |
 | 1 Warning in JetMatchingMadgraph:init: No xqcut |
 | |
 *------- End PYTHIA Error and Warning Messages Statistics ------------------------------------------------------*

Question information

Language:
English Edit question
Status:
Solved
For:
WHIZARD Edit question
Assignee:
Juergen Reuter Edit question
Last query:
Last reply:
Revision history for this message
Simon BraƟ (sbrass) said :
#1

Dear Asam,

as far as we can remember, we had not such a problem in recent times.

I can only infer from the P8 error message that there is a hiccup in the hadronization treatment of low mass systems, i.e. MiniStringFragmentation.
(I just checked with a debugger thate error appears at least in MiniStringFragmentation::fragment for c-cbar or s-sbar systems in the final state.)

We tested your Sindarin with our direct Pythia8 interface, and we find the same issue.
(Our interface comes with the benefit that we drop the prone event and can continue the shower and hadronization with Pythia8.)

We discussed some possible issues arising from missing information in the LHE records, e.g. keeping beam remnants (?keep_remnants = true in your Sindarin), however, this doesn't seem to fix the problem.

I would suggest that you contact the Pythia8 developers, and put us in CC: <email address hidden>.

Cheers,
Simon

Revision history for this message
Aram Apyan (arapyan) said :
#2

Hi Simon,

Ok thanks for taking a look. I contacted the Pythia8 developers (with <email address hidden> in CC).

Best,

Aram

Revision history for this message
Juergen Reuter (j.r.reuter) said :
#3

This has been answere by Steve Mrenna from Pythia:
"Your LHE file contains quarks and antiquarks with tiny energies.
There is no way to hadronize a q-qbar system with mass < pion_mass.
Maybe you should run wizard using either some cuts on the mass of the q-qbar
pair or using constituent quark masses (and not current mass ones)."
So this needs indeed some cuts or clustering to make infrared safe.

Revision history for this message
Juergen Reuter (j.r.reuter) said :
#4

Marked as solved.