Forcing Tau leptons to undergo a BSM decay

Asked by HH on 2020-12-05

Dear experts,

I need to simulate a process in which the Tau lepton experiences a beyond the SM (BSM) decay. I tried generating the events, but I found out that in the .lhe file (before showering and detector simulation) the Tau lepton undergoes the desired BSM decay while in the final root file (showered with PYTHIA8 and analysed by DELPHES) that Tau lepton undergoes a SM decay. Looking at the PYTHIA8 log file, in the "hard process", Tau is decayed through the BSM mode, while in the "complete event", the same Tau is decayed through a SM decay mode. I used the below commands to generate events:
generate e+ e- > ta+ ta- weighted<=99, ta- > X- Y
add process e+ e- > ta+ ta- weighted<=99, ta+ > X+ Y
where taons decay to X and Y particles.

It seems PYTHIA8 does NOT notice that Tau has already decayed in Mad level. And therefore performs showering as usual.

Would you please let me know how I can generate such a process?

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
HH
Solved:
2020-12-07
Last query:
2020-12-07
Last reply:
2020-12-07

Hi,

I doubt that I will be able to help you. I can take a look at one of the event to see if I spot something funny.
But if not then you will need to contact the pythia8 authors.

Cheers,

Olivier

HH (hh-madgrapher) said : #2

I encountered the same problem when trying to simulate only one of the processes. You can replace X with electron or muon. Y is a BSM neutral particle. I tried all cases and faced the same problem.

It seems that MadGraph should send a signal to PYTHIA to prevent it from decaying the Tau lepton (which has already decayed in Mad level). How does MdGraph do this?

The event file should have that information (could you copy paste one event here).
After that I would have expect PY8 to keep such decay and not remove it...
But maybe you would need to change a flag for the tau but I do not know which one (I would refer you to the PY8 manual)

Cheers,

Olivier

HH (hh-madgrapher) said : #4

I don't know if it is relevant, but I see the below error while MadGraph is running.

generate_events run_01_0 -f
Generating 50 events with run name run_01_0
survey run_01_0
INFO: compile directory
Traceback (most recent call last):
  File "write_param_card.py", line 178, in <module>
    ParamCardWriter('./param_card.dat', generic=True)
  File "write_param_card.py", line 29, in __init__
    self.write_card(list_of_parameters)
  File "write_param_card.py", line 83, in write_card
    from functools import cmp_to_key
ImportError: cannot import name cmp_to_key
compile Source Directory
Using random number seed offset = 21
INFO: Running Survey

HH (hh-madgrapher) said : #5

Thanks. In the following you can see the material you requested:

.lhe file:

<LesHouchesEvents version="3.0">
<header>
<!--
#*********************************************************************
# *
# MadGraph5_aMC@NLO *
# *
# Going Beyond *
# *
# http://madgraph.hep.uiuc.edu *
# http://madgraph.phys.ucl.ac.be *
# http://amcatnlo.cern.ch *
# *
# The MadGraph5_aMC@NLO team *
# *
#....................................................................*
# *
# This file contains all the information necessary to reproduce *
# the events generated: *
# *
# 1. software version *
# 2. proc_card : code generation info including model *
# 3. param_card : model primary parameters in the LH format *
# 4. run_card : running parameters (collider and cuts) *
# 5. pythia_card : present only if pythia has been run *
# 6. pgs_card : present only if pgs has been run *
# 7. delphes_cards : present only if delphes has been run *
# *
# *
#*********************************************************************
-->
<MGVersion>
#2.6.6
</MGVersion>
<MG5ProcCard>
<![CDATA[
#************************************************************
#* MadGraph5_aMC@NLO *
#* *
#* * * *
#* * * * * *
#* * * * * 5 * * * * *
#* * * * * *
#* * * *
#* *
#* *
#* VERSION 2.6.6 2018-06-28 *
#* *
#* The MadGraph5_aMC@NLO Development Team - Find us at *
#* https://server06.fynu.ucl.ac.be/projects/madgraph *
#* *
#************************************************************
#* *
#* Command File for MadGraph5_aMC@NLO *
#* *
#* run as ./bin/mg5_aMC filename *
#* *
#************************************************************
set default_unset_couplings 99
set group_subprocesses Auto
set ignore_six_quark_processes False
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
import model /data/tata2llax1000-rh-\
cVAet1/models/linear_UFO
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
generate e+ e- > ta+ ta-, ta- > e- ax
output tata2llax1000-rh-cVAet1
]]>
</MG5ProcCard>
<MGProcCard>
#*********************************************************************
# MadGraph/MadEvent *
# http://madgraph.hep.uiuc.edu *
# *
# proc_card.dat *
#*********************************************************************
# *
# This Files is generated by MADGRAPH 5 *
# *
# WARNING: This Files is generated for MADEVENT (compatibility issue)*
# This files is NOT a valid MG4 proc_card.dat *
# Running this in MG4 will NEVER reproduce the result of MG5*
# *
#*********************************************************************
#*********************************************************************
# Process(es) requested : mg2 input *
#*********************************************************************
# Begin PROCESS # This is TAG. Do not modify this line
e+ e- > ta+ ta- , ta- > e- ax #Process
# Be carefull the coupling are here in MG5 convention

end_coup # End the couplings input

done # this tells MG there are no more procs
# End PROCESS # This is TAG. Do not modify this line
#*********************************************************************
# Model information *
#*********************************************************************
# Begin MODEL # This is TAG. Do not modify this line
ALP_linear_LFV_UFO
# End MODEL # This is TAG. Do not modify this line
#*********************************************************************
# Start multiparticle definitions *
#*********************************************************************
# Begin MULTIPARTICLES # This is TAG. Do not modify this line

# End MULTIPARTICLES # This is TAG. Do not modify this line
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#*********************************************************************
# MadGraph5_aMC@NLO *
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# Some notation/conventions: *
# *
# Lines starting with a '# ' are info or comments *
# *
# mind the format: value = variable ! comment *
# *
# To display more options, you can type the command: *
# update full_run_card *
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#
#*******************
# Running parameters
#*******************
#
#*********************************************************************
# Tag name for the run (one word) *
#*********************************************************************
  tag_1 = run_tag ! name of the run
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# Number of events and rnd seed *
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  50 = nevents ! Number of unweighted events requested
 21 = iseed ! rnd seed (0=assigned automatically=default))
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# Collider type and energy *
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# 3=photon from electron *
#*********************************************************************
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  0 = lpp2 ! beam 2 type
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  nn23lo1 = pdlabel ! PDF set
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# To see heavy ion options: type "update ion_pdf"
#*********************************************************************
# Renormalization and factorization scales *
#*********************************************************************
  False = fixed_ren_scale ! if .true. use fixed ren scale
  False = fixed_fac_scale ! if .true. use fixed fac scale
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  average = event_norm ! average/sum. Normalization of the weight in the LHEF

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# Matching parameter (MLM only)
#*********************************************************************
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  False = chcluster ! cluster only according to channel diag
  5 = asrwgtflavor ! highest quark flavor for a_s reweight
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  0 = nhel ! using helicities importance sampling or not.
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# Generation bias, check the wiki page below for more information: *
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  None = bias_module ! Bias type of bias, [None, ptj_bias, -custom_folder-]
  {} = bias_parameters ! Specifies the parameters of the module.
#
#*******************************
# Parton level cuts definition *
#*******************************
#
#
#*********************************************************************
# BW cutoff (M+/-bwcutoff*Gamma) ! Define on/off-shell for "$" and decay
#*********************************************************************
  15.0 = bwcutoff ! (M+/-bwcutoff*Gamma)
#*********************************************************************
# Apply pt/E/eta/dr/mij/kt_durham cuts on decay products or not
# (note that etmiss/ptll/ptheavy/ht/sorted cuts always apply)
#*********************************************************************
  False = cut_decays ! Cut decay products
#*********************************************************************
# Standard Cuts *
#*********************************************************************
# Minimum and maximum pt's (for max, -1 means no cut) *
#*********************************************************************
  20.0 = ptj ! minimum pt for the jets
  0.0 = ptb ! minimum pt for the b
  10.0 = pta ! minimum pt for the photons
  10.0 = ptl ! minimum pt for the charged leptons
  0.0 = misset ! minimum missing Et (sum of neutrino's momenta)
  -1.0 = ptjmax ! maximum pt for the jets
  -1.0 = ptbmax ! maximum pt for the b
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  -1.0 = ptlmax ! maximum pt for the charged leptons
  -1.0 = missetmax ! maximum missing Et (sum of neutrino's momenta)
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#*********************************************************************
# Minimum and maximum E's (in the center of mass frame) *
#*********************************************************************
  0.0 = ej ! minimum E for the jets
  0.0 = eb ! minimum E for the b
  0.0 = ea ! minimum E for the photons
  0.0 = el ! minimum E for the charged leptons
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  -1.0 = ebmax ! maximum E for the b
  -1.0 = eamax ! maximum E for the photons
  -1.0 = elmax ! maximum E for the charged leptons
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#*********************************************************************
# Maximum and minimum absolute rapidity (for max, -1 means no cut) *
#*********************************************************************
  5.0 = etaj ! max rap for the jets
  -1.0 = etab ! max rap for the b
  2.5 = etaa ! max rap for the photons
  2.5 = etal ! max rap for the charged leptons
  0.0 = etajmin ! min rap for the jets
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#*********************************************************************
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  0.4 = drjj ! min distance between jets
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  0.4 = draj ! min distance between gamma and jet
  0.4 = drjl ! min distance between jet and lepton
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  0.0 = drbl ! min distance between b and lepton
  0.4 = dral ! min distance between gamma and lepton
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  -1.0 = drbjmax ! max distance between b and jet
  -1.0 = drajmax ! max distance between gamma and jet
  -1.0 = drjlmax ! max distance between jet and lepton
  -1.0 = drabmax ! max distance between gamma and b
  -1.0 = drblmax ! max distance between b and lepton
  -1.0 = dralmax ! maxdistance between gamma and lepton
#*********************************************************************
# Minimum and maximum invariant mass for pairs *
# WARNING: for four lepton final state mmll cut require to have *
# different lepton masses for each flavor! *
#*********************************************************************
  0.0 = mmjj ! min invariant mass of a jet pair
  0.0 = mmbb ! min invariant mass of a b pair
  0.0 = mmaa ! min invariant mass of gamma gamma pair
  0.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
  -1.0 = mmjjmax ! max invariant mass of a jet pair
  -1.0 = mmbbmax ! max invariant mass of a b pair
  -1.0 = mmaamax ! max invariant mass of gamma gamma pair
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  {} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
  {'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
                       ! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
#*********************************************************************
# Minimum and maximum invariant mass for all letpons *
#*********************************************************************
  0.0 = mmnl ! min invariant mass for all letpons (l+- and vl)
  -1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
#*********************************************************************
# Minimum and maximum pt for 4-momenta sum of leptons *
#*********************************************************************
  0.0 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)
  -1.0 = ptllmax ! Maximum pt for 4-momenta sum of leptons(l and vl)
#*********************************************************************
# Inclusive cuts *
#*********************************************************************
  0.0 = ptheavy ! minimum pt for at least one heavy final state
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  0.0 = xptb ! minimum pt for at least one b
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  0.0 = xptl ! minimum pt for at least one charged lepton
#*********************************************************************
# Control the pt's of the jets sorted by pt *
#*********************************************************************
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  -1.0 = ptj2max ! maximum pt for the second jet in pt
  -1.0 = ptj3max ! maximum pt for the third jet in pt
  -1.0 = ptj4max ! maximum pt for the fourth jet in pt
  0 = cutuse ! reject event if fails any (0) / all (1) jet pt cuts
#*********************************************************************
# Control the pt's of leptons sorted by pt *
#*********************************************************************
  0.0 = ptl1min ! minimum pt for the leading lepton in pt
  0.0 = ptl2min ! minimum pt for the second lepton in pt
  0.0 = ptl3min ! minimum pt for the third lepton in pt
  0.0 = ptl4min ! minimum pt for the fourth lepton in pt
  -1.0 = ptl1max ! maximum pt for the leading lepton in pt
  -1.0 = ptl2max ! maximum pt for the second lepton in pt
  -1.0 = ptl3max ! maximum pt for the third lepton in pt
  -1.0 = ptl4max ! maximum pt for the fourth lepton in pt
#*********************************************************************
# Control the Ht(k)=Sum of k leading jets *
#*********************************************************************
  0.0 = htjmin ! minimum jet HT=Sum(jet pt)
  -1.0 = htjmax ! maximum jet HT=Sum(jet pt)
  0.0 = ihtmin !inclusive Ht for all partons (including b)
  -1.0 = ihtmax !inclusive Ht for all partons (including b)
  0.0 = ht2min ! minimum Ht for the two leading jets
  0.0 = ht3min ! minimum Ht for the three leading jets
  0.0 = ht4min ! minimum Ht for the four leading jets
  -1.0 = ht2max ! maximum Ht for the two leading jets
  -1.0 = ht3max ! maximum Ht for the three leading jets
  -1.0 = ht4max ! maximum Ht for the four leading jets
#***********************************************************************
# Photon-isolation cuts, according to hep-ph/9801442 *
# When ptgmin=0, all the other parameters are ignored *
# When ptgmin>0, pta and draj are not going to be used *
#***********************************************************************
  0.0 = ptgmin ! Min photon transverse momentum
  0.4 = r0gamma ! Radius of isolation code
  1.0 = xn ! n parameter of eq.(3.4) in hep-ph/9801442
  1.0 = epsgamma ! epsilon_gamma parameter of eq.(3.4) in hep-ph/9801442
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#*********************************************************************
# WBF cuts *
#*********************************************************************
  0.0 = xetamin ! minimum rapidity for two jets in the WBF case
  0.0 = deltaeta ! minimum rapidity for two jets in the WBF case
#***********************************************************************
# Turn on either the ktdurham or ptlund cut to activate *
# CKKW(L) merging with Pythia8 [arXiv:1410.3012, arXiv:1109.4829] *
#***********************************************************************
  -1.0 = ktdurham
  0.4 = dparameter
  -1.0 = ptlund
  1, 2, 3, 4, 5, 6, 21 = pdgs_for_merging_cut ! PDGs for two cuts above
#*********************************************************************
# maximal pdg code for quark to be considered as a light jet *
# (otherwise b cuts are applied) *
#*********************************************************************
  4 = maxjetflavor ! Maximum jet pdg code
#*********************************************************************
#
#*********************************************************************
# Store info for systematics studies *
# WARNING: Do not use for interference type of computation *
#*********************************************************************
  False = use_syst ! Enable systematics studies
#
  systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments ! see: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Systematics#Systematicspythonmodule
# Syscalc is deprecated but to see the associate options type'update syscalc'#*********************************************************************
# Additional hidden parameters
#*********************************************************************
  ['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments # Choose the argment to pass to the systematics command. like --mur=0.25,1,4. Look at the help of the systematics function for more details.
]]>
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<slha>
######################################################################
## PARAM_CARD AUTOMATICALY GENERATED BY MG5 ####
######################################################################
###################################
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###################################
BLOCK ALPPARS #
      1 1.000000e+03 # fa
      2 0.000000e+00 # cgtil
      3 0.000000e+00 # cwtil
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      8 1.000000e+00 # cvet
      9 0.000000e+00 # cvmt
      10 0.000000e+00 # caem
      11 1.000000e+00 # caet
      12 0.000000e+00 # camt
      13 0.000000e+00 # cunifdl
      14 1.000000e+00 # caee
      15 1.000000e+00 # camm
      16 1.000000e+00 # catt
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###################################
BLOCK CKMBLOCK #
      1 2.277360e-01 # cabi
###################################
## INFORMATION FOR MASS
###################################
BLOCK MASS #
      1 5.040000e-03 # md
      2 2.550000e-03 # mu
      3 1.010000e-01 # ms
      4 1.270000e+00 # mc
      5 4.700000e+00 # mb
      6 1.720000e+02 # mt
      11 5.110000e-04 # me
      13 1.056600e-01 # mmu
      15 1.777000e+00 # mta
      23 9.118760e+01 # mz
      25 1.250000e+02 # mh
      9000005 1.000000e-03 # ma
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      14 0.000000e+00 # vm : 0.0
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      21 0.000000e+00 # g : 0.0
      22 0.000000e+00 # a : 0.0
      24 7.982436e+01 # w+ : cmath.sqrt(mz__exp__2/2. + cmath.sqrt(mz__exp__4/4. - (aew*cmath.pi*mz__exp__2)/(gf*sqrt__2)))
###################################
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###################################
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      3 1.184000e-01 # as
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      5 4.700000e+00 # ymb
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      11 5.110000e-04 # yme
      13 1.056600e-01 # ymm
      15 1.777000e+00 # ymtau
###################################
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###################################
DECAY 6 1.508336e+00 # wt
DECAY 23 2.495200e+00 # wz
DECAY 24 2.085000e+00 # ww
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DECAY 5 0.000000e+00 # b : 0.0
DECAY 11 0.000000e+00 # e- : 0.0
DECAY 12 0.000000e+00 # ve : 0.0
DECAY 13 3.009468e-19 # mu- : ((caem__exp__2*cunilfv__exp__2 + cunilfv__exp__2*cvem__exp__2)*(1 - ma__exp__2/mmu__exp__2)**2*mmu__exp__3)/(64.*fa__exp__2*cmath.pi) + 0.00016798246332228145*gf__exp__2*mmu__exp__5
DECAY 14 0.000000e+00 # vm : 0.0
DECAY 15 5.581875e-08 # ta- : ((caet__exp__2*cunilfv__exp__2 + cunilfv__exp__2*cvet__exp__2)*(1 - ma__exp__2/mta__exp__2)**2*mta__exp__3)/(64.*fa__exp__2*cmath.pi) + ((camt__exp__2*cunilfv__exp__2 + cunilfv__exp__2*cvmt__exp__2)*(1 - ma__exp__2/mta__exp__2)**2*mta__exp__3)/(64.*fa__exp__2*cmath.pi) + (165*mta__exp__5*wmuon)/(29.*mmu__exp__5)
DECAY 16 0.000000e+00 # vt : 0.0
DECAY 21 0.000000e+00 # g : 0.0
DECAY 22 0.000000e+00 # a : 0.0
DECAY 9000005 0.000000e+00 # ax : 0.0
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###################################
BLOCK QNUMBERS 9000005 # ax
      1 0 # 3 times electric charge
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</header>
<init>
-11 11 5.000000e+02 5.000000e+02 0 0 247000 247000 -4 1
1.880900e-11 2.016100e-13 1.880900e-11 1
<generator name='MadGraph5_aMC@NLO' version='2.6.6'>please cite 1405.0301 </generator>
</init>
<event>
 6 1 +1.8809000e-11 5.00000000e+02 7.81860800e-03 9.42494000e-02
      -11 -1 0 0 0 0 +0.0000000000e+00 +0.0000000000e+00 +5.0000000000e+02 5.0000000000e+02 5.1100000000e-04 0.0000e+00 -1.0000e+00
       11 -1 0 0 0 0 -0.0000000000e+00 -0.0000000000e+00 -5.0000000000e+02 5.0000000000e+02 5.1100000000e-04 0.0000e+00 1.0000e+00
       15 2 1 2 0 0 -1.5947254295e+02 -2.4113131462e+02 +4.0794734884e+02 5.0000000000e+02 1.7770005069e+00 0.0000e+00 0.0000e+00
      -15 1 1 2 0 0 +1.5947254295e+02 +2.4113131462e+02 -4.0794734884e+02 5.0000000000e+02 1.7770000000e+00 0.0000e+00 1.0000e+00
       11 1 3 3 0 0 -2.5018892974e+01 -3.8642915526e+01 +6.5777285933e+01 8.0286183562e+01 5.1100000000e-04 0.0000e+00 1.0000e+00
  9000005 1 3 3 0 0 -1.3445364997e+02 -2.0248839910e+02 +3.4217006291e+02 4.1971381644e+02 1.0000000000e-03 0.0000e+00 0.0000e+00
</event>
<event>
 6 1 +1.8809000e-11 5.00000000e+02 7.81860800e-03 9.42494000e-02
      -11 -1 0 0 0 0 +0.0000000000e+00 +0.0000000000e+00 +5.0000000000e+02 5.0000000000e+02 5.1100000000e-04 0.0000e+00 -1.0000e+00
       11 -1 0 0 0 0 -0.0000000000e+00 -0.0000000000e+00 -5.0000000000e+02 5.0000000000e+02 5.1100000000e-04 0.0000e+00 1.0000e+00
       15 2 1 2 0 0 +4.4899826207e+01 +4.6485170120e+02 -1.7858819605e+02 5.0000000000e+02 1.7770002381e+00 0.0000e+00 0.0000e+00
      -15 1 1 2 0 0 -4.4899826207e+01 -4.6485170120e+02 +1.7858819605e+02 5.0000000000e+02 1.7770000000e+00 0.0000e+00 1.0000e+00
       11 1 3 3 0 0 +3.0330810344e+00 +2.7148728303e+01 -1.0533964387e+01 2.9278275821e+01 5.1100000000e-04 0.0000e+00 1.0000e+00
  9000005 1 3 3 0 0 +4.1866745173e+01 +4.3770297290e+02 -1.6805423166e+02 4.7072172418e+02 1.0000000000e-03 0.0000e+00 0.0000e+00
</event>

A piece of PYTHIA8 log file which shows an apparent inconsistency:

 -------- 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 1000.000 1000.000
     1 -11 (e+) -12 0 0 3 0 0 0 0.000 0.000 500.000 500.000 0.001
     2 11 (e-) -12 0 0 4 0 0 0 0.000 0.000 -500.000 500.000 0.001
     3 -11 (e+) -21 1 0 5 6 0 0 0.000 0.000 500.000 500.000 0.000
     4 11 (e-) -21 2 0 5 6 0 0 -0.000 -0.000 -500.000 500.000 0.000
     5 15 (tau-) -22 3 4 7 8 0 0 -159.473 -241.131 407.947 500.000 1.777
     6 -15 tau+ 23 3 4 0 0 0 0 159.473 241.131 -407.947 500.000 1.777
     7 11 e- 23 5 0 0 0 0 0 -25.019 -38.643 65.777 80.286 0.001
     8 9000005 ax 23 5 0 0 0 0 0 -134.454 -202.488 342.170 419.714 0.001
                                   Charge sum: 0.000 Momentum sum: 0.000 -0.000 0.000 1000.000 1000.000

 -------- End PYTHIA Event Listing -----------------------------------------------------------------------------------------------

 -------- PYTHIA Event Listing (complete event) ---------------------------------------------------------------------------------

    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 1000.000 1000.000
     1 -11 (e+) -12 0 0 3 0 0 0 0.000 0.000 500.000 500.000 0.001
     2 11 (e-) -12 0 0 4 0 0 0 0.000 0.000 -500.000 500.000 0.001
     3 -11 (e+) -21 1 0 5 6 0 0 0.000 0.000 500.000 500.000 0.000
     4 11 (e-) -21 2 0 5 6 0 0 -0.000 -0.000 -500.000 500.000 0.000
     5 15 (tau-) -22 3 4 10 13 0 0 -159.473 -241.131 407.947 500.000 1.777
     6 -15 (tau+) -23 3 4 7 9 0 0 159.473 241.131 -407.947 500.000 1.777
     7 -16 nu_taubar 91 6 0 0 0 0 0 90.740 138.449 -232.905 285.739 0.000
     8 -11 e+ 91 6 0 0 0 0 0 42.461 63.017 -107.502 131.646 0.001
     9 12 nu_e 91 6 0 0 0 0 0 26.271 39.666 -67.540 82.615 0.000
    10 16 nu_tau 91 5 0 0 0 0 0 -73.929 -112.369 190.012 232.802 0.000
    11 -211 pi- 91 5 0 0 0 0 0 -15.991 -24.430 41.589 50.816 0.140
    12 -211 pi- 91 5 0 0 0 0 0 -20.195 -30.821 51.661 63.456 0.140
    13 211 pi+ 91 5 0 0 0 0 0 -49.358 -73.511 124.685 152.927 0.140
                                   Charge sum: 0.000 Momentum sum: -0.000 -0.000 0.000 1000.000 1000.000

 -------- End PYTHIA Event Listing -----------------------------------------------------------------------------------------------

Looks like the UFO model that you are using is requiring python2.7 at minimum to run and that you are runninng with python2.6 (I guess).

The official version of MG5aMC does not support anymore python2.6 and therefore the official UFO model generated with a recent version of FeynRules does not support that version of python anymore (this version is out of support since more than 6 years and even python2.7 is out of support since a year actually).

This explains the error that you quote. I do not think that this creates serious issue but it can forbid some update of the param-card and forbids the consistency check (and the auto-update of that card if needed).

So I would suggest to move to MG5aMC 2.8.2 which is using python3 by default (needs python3.7 as minimal version).

I noted that you did not specify the BR for the tau lepton which I think is needed if you want pythia to decay the second tau.
And since this is a SM particles you might have two issues with pythia:
1. it will overwrite your width/... and simply assumes the SM
2. you will to add tag to force Pythia to decay only to SM.

The event seems coherent to me and the issue should be on the pythia side, I would invite you to read the pythia manual to learn the flag associated to tau decay and contact pythia author if you do not find a way to do your simulation.

Cheers,

Olivier

HH (hh-madgrapher) said : #7

Thanks for your answer. I will try to find the solution in PY8 manual. By the way, I don't understand this: "I noted that you did not specify the BR for the tau lepton which I think is needed if you want pythia to decay the second tau." I don't know how to set the Branching Ratio for a particle. The only way I know is to set the decay width. In the SM UFO model, the decay width of Tau is by default set to 0. In order to be able to decay Tau in Mad level, I replaced 0 with a formula which gives the SM decay width + BSM decay width of Tau. This is the total decay width of Tau. I thought this gives enough information to MadGraph and PY8 for handling decays of Tau.

I read PY8 manual looking for flags controlling Tau decays. I didn't find a relevant flag. So I pursued my question by asking the PY8 developer for a solution.

Thanks for your help.

This is enough for madgraph but not for pythia.

You will find how to specify the BR in this paper:
https://arxiv.org/pdf/hep-ph/0311123.pdf

Cheers,

Olivier

HH (hh-madgrapher) said : #9

Thanks for your advice. I read PY8 manual and set needed variables to control PY8. But I still have a problem which seems to be on MadGraph side.

I think I know what the problem is. It may be related to the issue reported here https://answers.launchpad.net/mg5amcnlo/+question/670297. Now I explain what is going on:

I added the desired BSM decay channel and its BR to PY8 decay table by
set pythia8_card 15:rescaleBR .9
set pythia8_card 15:addChannel 0 .1 0 11 9000005
Then I used the commands
set pythia8_card 15:onMode off
set pythia8_card 15:onPosIfAny 9000005
set pythia8_card 15:onNegIfAny 16
to first make all decays OFF for Tau, then make BSM decay ON for Tau- and then make SM decays ON for Tau+. I expected these commands to produce the process
e+ e- > ta+ ta-, ta- > e- ax
with Tau+ undergoes a SM decay. However, looking at the PY8 log file, I found out that all of the decay modes of Tau are OFF. In fact it seems that the order of the commands has been changed by MadGraph in such a way that the command
set pythia8_card 15:onMode off
which must be first, has been moved to the last line. Therefore all decays are off.

Would you please let me know how I can make MadGraph to produce a proper PY8 card?

Here https://answers.launchpad.net/mg5amcnlo/+question/670297 you have given a solution but I don't know where the banner.py file is. Also I don't understand the piece of code you wrote there.

Thanks in advance

Are you using the latest version of the code?
This should not happen anymore.

Cheers,

Olivier

> On 6 Dec 2020, at 16:50, HH <email address hidden> wrote:
>
> Question #694362 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/694362
>
> Status: Answered => Open
>
> HH is still having a problem:
> Thanks for your advice. I read PY8 manual and set needed variables to
> control PY8. But I still have a problem which seems to be on MadGraph
> side.
>
> I think I know what the problem is. It may be related to the issue
> reported here https://answers.launchpad.net/mg5amcnlo/+question/670297.
> Now I explain what is going on:
>
> I added the desired BSM decay channel and its BR to PY8 decay table by
> set pythia8_card 15:rescaleBR .9
> set pythia8_card 15:addChannel 0 .1 0 11 9000005
> Then I used the commands
> set pythia8_card 15:onMode off
> set pythia8_card 15:onPosIfAny 9000005
> set pythia8_card 15:onNegIfAny 16
> to first make all decays OFF for Tau, then make BSM decay ON for Tau- and then make SM decays ON for Tau+. I expected these commands to produce the process
> e+ e- > ta+ ta-, ta- > e- ax
> with Tau+ undergoes a SM decay. However, looking at the PY8 log file, I found out that all of the decay modes of Tau are OFF. In fact it seems that the order of the commands has been changed by MadGraph in such a way that the command
> set pythia8_card 15:onMode off
> which must be first, has been moved to the last line. Therefore all decays are off.
>
> Would you please let me know how I can make MadGraph to produce a proper
> PY8 card?
>
> Here https://answers.launchpad.net/mg5amcnlo/+question/670297 you have
> given a solution but I don't know where the banner.py file is. Also I
> don't understand the piece of code you wrote there.
>
> Thanks in advance
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

HH (hh-madgrapher) said : #11

I am using version 2.6.6. Unfortunately because of outdated Python version 2.6.6 I cannot use the latest version. Is there any way to do to overcome this problem in my current MG5 version?

HH (hh-madgrapher) said : #12

I am using MG5 version 2.6.6. Unfortunately because of my outdated Python version 2.6.6 I cannot use the latest version of MG5. Is there any way to do to overcome this problem in my current MG5 version?

The easiest should be to install a second version of python on your system.

Otherwise, you can also try to use MG5aMC 2.7.3 which should still support python 2.6.6. (I doubt that issue is fixed in 2.7.3 but might be worth the try)

Or use this alpha development version (you need to install the bazaar control version system)
bzr branch lp:~maddevelopers/mg5amcnlo/2.8.3.py2
You can also find link to night build tarball here:
https://code.launchpad.net/~maddevelopers/mg5amcnlo/2.8.3.py2
(you have to click on the number associated to the latest version available)

Obviously such alpha version is not suppose to be used in production since they are not validated (and therefore sometimes suffer major bug)

Cheers,

Olivier

HH (hh-madgrapher) said : #14

Thanks for your help Olivier.