MadGraph5_aMC@NLO

Gridpack minimal number of events per run

Asked by Grégory Hammad

Dear all,

we are trying to produce a significant amount of events (>100M) for the following processes:
sm_no-masses
p p > l+ l- (+Xj), X=1,2,3,4
using gridpacks (MG5_aMC_v2.1.2.tgz)

During the creation of the gridpack, if we understand correctly, the number of events specified in the run_card has no influence, although it is set to 100k. Could you confirm?

Now concerning the LHE files production with these gridpacks, we are able to produce 100k events per run for low jet multiplicities (X=1,2) but not for higher multiplicities. We understand this is due to some divergences that could be avoided by playing with some of the cuts in the run_card (although we played quite a lot and never found the correct ones... if mllmin=10 and mllmax=50, neither a ptl=5, nor a pta=5, nor a drll=0.1 works. Strangely enough though, we do get 100k events when setting a drll=0.15?? Why we should specify a drll value remains a mystery since there is mllmin cut at 10, see run_card below(*).)
However, we observed something we did not expect: we lowered the number of events per run and observed a higher chance to produce the requested number of events.
So, here is my question; is there a minimal number of events/run for a given gridpack? It is written in the FAQ pages concerning the gridpacks that the sub-processes probed during a certain run are random (with a weight corresponding to their contribution to the overall cross-section). The number of events/run defines the granularity but besides that, if one performs a lot of runs, lowering the number of events should not be an issue as it will ultimately probe even the small sub-processes. Is that correct?
If not, and if indeed, lowering the number of events/run (from 100k to 10k for instance) leads to neglect some sub-processes, is there a way to verify if the neglected sub-processes could indeed be neglected?

Thank you in advance.

Regards,

Grégory

(*)
#*********************************************************************
# MadGraph5_aMC@NLO *
# *
# run_card.dat MadEvent *
# *
# This file is used to set the parameters of the run. *
# *
# Some notation/conventions: *
# *
# Lines starting with a '# ' are info or comments *
# *
# mind the format: value = variable ! comment *
#*********************************************************************
#
#*******************
# Running parameters
#*******************
#
#*********************************************************************
# Tag name for the run (one word) *
#*********************************************************************
  tag_1 = run_tag ! name of the run
#*********************************************************************
# Run to generate the grid pack *
#*********************************************************************
  .false. = gridpack !True = setting up the grid pack
#*********************************************************************
# Number of events and rnd seed *
# Warning: Do not generate more than 1M events in a single run *
# If you want to run Pythia, avoid more than 50k events in a run. *
#*********************************************************************
 100000 = nevents ! Number of unweighted events requested
      0 = iseed ! rnd seed (0=assigned automatically=default))
#*********************************************************************
# Collider type and energy *
# lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
# 3=photon from electron *
#*********************************************************************
        1 = lpp1 ! beam 1 type
        1 = lpp2 ! beam 2 type
     6500 = ebeam1 ! beam 1 total energy in GeV
     6500 = ebeam2 ! beam 2 total energy in GeV
#*********************************************************************
# Beam polarization from -100 (left-handed) to 100 (right-handed) *
#*********************************************************************
        0 = polbeam1 ! beam polarization for beam 1
        0 = polbeam2 ! beam polarization for beam 2
#*********************************************************************
# PDF CHOICE: this automatically fixes also alpha_s and its evol. *
#*********************************************************************
 'cteq6l1' = pdlabel ! PDF set
#*********************************************************************
# Renormalization and factorization scales *
#*********************************************************************
 F = fixed_ren_scale ! if .true. use fixed ren scale
 F = fixed_fac_scale ! if .true. use fixed fac scale
 91.1880 = scale ! fixed ren scale
 91.1880 = dsqrt_q2fact1 ! fixed fact scale for pdf1
 91.1880 = dsqrt_q2fact2 ! fixed fact scale for pdf2
 1 = scalefact ! scale factor for event-by-event scales
#*********************************************************************
# Matching - Warning! ickkw > 1 is still beta
#*********************************************************************
 1 = ickkw ! 0 no matching, 1 MLM, 2 CKKW matching
 1 = highestmult ! for ickkw=2, highest mult group
 1 = ktscheme ! for ickkw=1, 1 Durham kT, 2 Pythia pTE
 1 = alpsfact ! scale factor for QCD emission vx
 F = chcluster ! cluster only according to channel diag
 T = pdfwgt ! for ickkw=1, perform pdf reweighting
 5 = asrwgtflavor ! highest quark flavor for a_s reweight
 T = clusinfo ! include clustering tag in output
#*********************************************************************
#**********************************************************
#
#**********************************************************
# Automatic ptj and mjj cuts if xqcut > 0
# (turn off for VBF and single top processes)
#**********************************************************
   T = auto_ptj_mjj ! Automatic setting of ptj and mjj
#**********************************************************
#
#**********************************
# BW cutoff (M+/-bwcutoff*Gamma)
#**********************************
  100 = bwcutoff ! (M+/-bwcutoff*Gamma)
#**********************************************************
# Apply pt/E/eta/dr/mij cuts on decay products or not
# (note that etmiss/ptll/ptheavy/ht/sorted cuts always apply)
#**********************************************************
   T = cut_decays ! Cut decay products
#*************************************************************
# Number of helicities to sum per event (0 = all helicities)
# 0 gives more stable result, but longer run time (needed for
# long decay chains e.g.).
# Use >=2 if most helicities contribute, e.g. pure QCD.
#*************************************************************
   0 = nhel ! Number of helicities used per event
#*******************
# Standard Cuts
#*******************
#
#*********************************************************************
# Minimum and maximum pt's (for max, -1 means no cut) *
#*********************************************************************
  0 = ptj ! minimum pt for the jets
  0 = ptb ! minimum pt for the b
  0 = pta ! minimum pt for the photons
  0 = ptl ! minimum pt for the charged leptons
  0 = misset ! minimum missing Et (sum of neutrino's momenta)
  0 = ptheavy ! minimum pt for one heavy final state
 1.0 = ptonium ! minimum pt for the quarkonium states
 -1 = ptjmax ! maximum pt for the jets
 -1 = ptbmax ! maximum pt for the b
 -1 = ptamax ! maximum pt for the photons
 -1 = ptlmax ! maximum pt for the charged leptons
 -1 = missetmax ! maximum missing Et (sum of neutrino's momenta)
#*********************************************************************
# Minimum and maximum E's (in the lab frame) *
#*********************************************************************
  0 = ej ! minimum E for the jets
  0 = eb ! minimum E for the b
  0 = ea ! minimum E for the photons
  0 = el ! minimum E for the charged leptons
 -1 = ejmax ! maximum E for the jets
 -1 = ebmax ! maximum E for the b
 -1 = eamax ! maximum E for the photons
 -1 = elmax ! maximum E for the charged leptons
#*********************************************************************
# Maximum and minimum absolute rapidity (for max, -1 means no cut) *
#*********************************************************************
  10 = etaj ! max rap for the jets
  -1 = etab ! max rap for the b
  10 = etaa ! max rap for the photons
  10 = etal ! max rap for the charged leptons
 0.6 = etaonium ! max rap for the quarkonium states
   0 = etajmin ! min rap for the jets
   0 = etabmin ! min rap for the b
   0 = etaamin ! min rap for the photons
   0 = etalmin ! main rap for the charged leptons
#*********************************************************************
# Minimum and maximum DeltaR distance *
#*********************************************************************
 0.001 = drjj ! min distance between jets
 0.001 = drbb ! min distance between b's
 0.001 = drll ! min distance between leptons
 0.001 = draa ! min distance between gammas
 0.001 = drbj ! min distance between b and jet
 0.001 = draj ! min distance between gamma and jet
 0.001 = drjl ! min distance between jet and lepton
 0.001 = drab ! min distance between gamma and b
 0.001 = drbl ! min distance between b and lepton
 0.001 = dral ! min distance between gamma and lepton
 -1 = drjjmax ! max distance between jets
 -1 = drbbmax ! max distance between b's
 -1 = drllmax ! max distance between leptons
 -1 = draamax ! max distance between gammas
 -1 = drbjmax ! max distance between b and jet
 -1 = drajmax ! max distance between gamma and jet
 -1 = drjlmax ! max distance between jet and lepton
 -1 = drabmax ! max distance between gamma and b
 -1 = drblmax ! max distance between b and lepton
 -1 = dralmax ! maxdistance between gamma and lepton
#*********************************************************************
# Minimum and maximum invariant mass for pairs *
#*********************************************************************
  0 = mmjj ! min invariant mass of a jet pair
  0 = mmbb ! min invariant mass of a b pair
  0 = mmaa ! min invariant mass of gamma gamma pair
 10 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
 -1 = mmjjmax ! max invariant mass of a jet pair
 -1 = mmbbmax ! max invariant mass of a b pair
 -1 = mmaamax ! max invariant mass of gamma gamma pair
 50 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
#*********************************************************************
# Minimum and maximum invariant mass for all letpons *
#*********************************************************************
 0 = mmnl ! min invariant mass for all letpons (l+- and vl)
 -1 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
#*********************************************************************
# Minimum and maximum pt for 4-momenta sum of leptons *
#*********************************************************************
 0 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)
 -1 = ptllmax ! Maximum pt for 4-momenta sum of leptons(l and vl)
#*********************************************************************
# Inclusive cuts *
#*********************************************************************
 0 = xptj ! minimum pt for at least one jet
 0 = xptb ! minimum pt for at least one b
 0 = xpta ! minimum pt for at least one photon
 0 = xptl ! minimum pt for at least one charged lepton
#*********************************************************************
# Control the pt's of the jets sorted by pt *
#*********************************************************************
 0 = ptj1min ! minimum pt for the leading jet in pt
 0 = ptj2min ! minimum pt for the second jet in pt
 0 = ptj3min ! minimum pt for the third jet in pt
 0 = ptj4min ! minimum pt for the fourth jet in pt
 -1 = ptj1max ! maximum pt for the leading jet in pt
 -1 = ptj2max ! maximum pt for the second jet in pt
 -1 = ptj3max ! maximum pt for the third jet in pt
 -1 = 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 = ptl1min ! minimum pt for the leading lepton in pt
 0 = ptl2min ! minimum pt for the second lepton in pt
 0 = ptl3min ! minimum pt for the third lepton in pt
 0 = ptl4min ! minimum pt for the fourth lepton in pt
 -1 = ptl1max ! maximum pt for the leading lepton in pt
 -1 = ptl2max ! maximum pt for the second lepton in pt
 -1 = ptl3max ! maximum pt for the third lepton in pt
 -1 = ptl4max ! maximum pt for the fourth lepton in pt
#*********************************************************************
# Control the Ht(k)=Sum of k leading jets *
#*********************************************************************
 0 = htjmin ! minimum jet HT=Sum(jet pt)
 -1 = htjmax ! maximum jet HT=Sum(jet pt)
 0 = ihtmin !inclusive Ht for all partons (including b)
 -1 = ihtmax !inclusive Ht for all partons (including b)
 0 = ht2min ! minimum Ht for the two leading jets
 0 = ht3min ! minimum Ht for the three leading jets
 0 = ht4min ! minimum Ht for the four leading jets
 -1 = ht2max ! maximum Ht for the two leading jets
 -1 = ht3max ! maximum Ht for the three leading jets
 -1 = 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 = 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
 .true. = isoEM ! isolate photons from EM energy (photons and leptons)
#*********************************************************************
# WBF cuts *
#*********************************************************************
 0 = xetamin ! minimum rapidity for two jets in the WBF case
 0 = deltaeta ! minimum rapidity for two jets in the WBF case
#*********************************************************************
# KT DURHAM CUT *
#*********************************************************************
 -1 = ktdurham
 0.4 = dparameter
#*********************************************************************
# maximal pdg code for quark to be considered as a light jet *
# (otherwise b cuts are applied) *
#*********************************************************************
 5 = maxjetflavor ! Maximum jet pdg code
#*********************************************************************
# Jet measure cuts *
#*********************************************************************
 10 = xqcut ! minimum kt jet measure between partons
#*********************************************************************
#
#*********************************************************************
# Store info for systematics studies *
# WARNING: If use_syst is T, matched Pythia output is *
# meaningful ONLY if plotted taking matchscale *
# reweighting into account! *
#*********************************************************************
   F = use_syst ! Enable systematics studies
#
#**************************************
# Parameter of the systematics study
# will be use by SysCalc (if install)
#**************************************
#
0.5 1 2 = sys_scalefact # Central scale factors
0.5 1 2 = sys_alpsfact # \alpha_s emission scale factors
30 50 = sys_matchscale # variation of merging scale
# PDF sets and number of members (0 or none for all members).
CT10nlo.LHgrid = sys_pdf # matching scales
# MSTW2008nlo68cl.LHgrid 1 = sys_pdf

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Rikkert Frederix Edit question
Last query:
Last reply:
Revision history for this message
Rikkert Frederix (frederix) said : 		#1

Dear Grégory,

For the gridpack creation, the number of nevents parameter is not used.

Indeed, an invariant mass cut on the leptons removes the divergence. There is no need for any other cut on the leptons. You can set the number of events to be generated by the grid pack as low as you like. Even setting it to 1000 or lower is still okay.

Best regards,
Rikkert

Revision history for this message
Adam Alloul (adam-alloul) said : 		#2

Dear Rikkert.

as I'm involved in the same project as Greg, I would like to add some comments to this issue. We have tried to generate 100k events with the only cut being 10 < inv. mass of leptons < 50 as can be seen in the run_card.dat posted by Greg. The problem is that the number of events that are actually generated by MG5 is way smaller than 100k (it's never the same but always much smaller 100k). We only found two ways to get the gridpack to produce as many events as we ask for:
  1) ask for a lower number of events (say 20k)
  2) ask for a minimum drll of 0.15

Our question is to understand if one of the above solutions is better than the other one or if this is hiding a deeper problem in MG5?

Thank you for your time.

Adam.

Revision history for this message
Rikkert Frederix (frederix) said : 		#3

Dear Adam,

I don't think there is a real problem. The thing I understand is that if you have a highly boosted lepton pair, an invariant mass cut of 10 GeV is a bit low and you are close to the photon IR singularity. Of course, a drll cut removes this phase-space region. If you generate a lot of events in a single go, you are more likely to hit this almost singularity more often than only requiring a small number of events. This reduces the unweighting efficiency enormously.

Therefore, I think it's okay to reduce the number of events per job, or to apply the cut.

Cheers,
Rik

Revision history for this message
Adam Alloul (adam-alloul) said : 		#4

Dear Rikkert,

thank you for your help, that solves our problem!

Cheers,

Adam.

Revision history for this message
Josh Bendavid (joshbendavid) said : 		#5

Hi,
Coming back to this,
We have seen a similar issue with LO gridpacks in 2.2.2 for multijet processes (will attach cards)

When generating events with the gridpack, requesting ~50k events per job, in the majority of jobs the number of events produced matches what was requested, but in some fraction it does not.

Practical questions.
1) Would we bias the sample by simply throwing out the lhe files for those jobs/random seeds where the number of events produced is lower than requested?

2) Would we bias the sample instead by simply keeping those lhe files with fewer events produced than requested.

Is either of the two above options preferred?

Thanks,
Josh

Revision history for this message
Josh Bendavid (joshbendavid) said : 		#6

Example cards which lead to this issue:
https://github.com/cms-sw/genproductions/blob/9599bc7c1606c89a883506411f5189fbda5c61c3/bin/MadGraph5_aMCatNLO/cards/production/13TeV/QCD_HT_LO_MLM/QCD_HT200to300/QCD_HT200to300_proc_card.dat
https://github.com/cms-sw/genproductions/blob/9599bc7c1606c89a883506411f5189fbda5c61c3/bin/MadGraph5_aMCatNLO/cards/production/13TeV/QCD_HT_LO_MLM/QCD_HT200to300/QCD_HT200to300_run_card.dat

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#7

Hi Josh,

>1) Would we bias the sample by simply throwing out the lhe files for those jobs/random seeds where the number of events
>produced is lower than requested?

If this happens only for a few number of run, then it should be safe to assume that the problem is linked to the integration grid and not to any physical effect. In that case, removing the event sample should be 100% fine.

> 2) Would we bias the sample instead by simply keeping those lhe files with fewer events produced than requested.

Those events are unweighted correctly and therefore the shape of those events only are correct. On the other hand, Alexis told us couple of years ago that CMS realised that such sample have slightly higher "error" than the equivalent sample generate normally.
I have never try to really traceback/check that statement, but it might be related in some border effect in the unweighting.

So I would advise method 1 to be safer ( if this is not too bad for efficiency)

Cheers,

Olivier

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