jet matching results in divergent xsection

Asked by Yong Du on 2019-10-15

Hi,

I read all relevant posts here but did not find one that is related to the question I have, so could you help me?

I was doing jet matching as follows (where H+/H- are the charged components of a real triplet):
1. generate p p > H+ H- j
add process p p > H+ H- j j
2. in the run card, I set auto_ptj_mjj to true and some positive number for xqcut.
3. I then set ptj=ptb=xqcut with drjj=drbj=drbb=0 as default.

I used MLM matching with CKKW merging and Pythia8 for parton showering. What I found is that, for xqcut<40, the effective luminosity is 0 and the corresponding xsection is infinity. When I set xqcut =40 or 50, the corresponding effective luminosity is O(10^-30~10^-100 pb^-1) with the corresponding xsection being of O(10^30~10^100 pb).

I have been playing with xqcut to get rid of the IR divergence and expect for the xqcut I had been using, the IR divergence shall already be taken care of by Pythia8 so the final result shall be finite. But it turns out the final xsection is divergent. Do you have any suggestion?

I'm using the latest version (v2.6.3.2) of MadGraph.

Thanks and best,
Yong

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Yong Du
Solved:
2019-10-17
Last query:
2019-10-17
Last reply:
2019-10-16

Hi,

> I used MLM matching with CKKW merging and Pythia8 for parton showering.

You can not combine two matching/merging scheme.
So either you use MLM or you use CKKW-L
CKKW is not implemented/supported at all in MG5aMC (since it requires additional changes in MG5aMC and that such method is not deprecated in favour of CKKW-L)

> the corresponding xsection being of O(10^30~10^100 pb).

The first step is to drop the matching/merging and check what is the cross-section of
> generate p p > H+ H- j
and check if this is finite or not.

Question for you here, why do not you start at
> generate p p > H+ H-
Is this process does not exist? Or should you request very hard cut on the jet (much harder than qcut)

Cheers,

Olivier
> On 15 Oct 2019, at 21:08, Yong Du <email address hidden> wrote:
>
> New question #685196 on MadGraph5_aMC@NLO:
> https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fanswers.launchpad.net%2Fmg5amcnlo%2F%2Bquestion%2F685196&amp;data=02%7C01%7C%7C6a6f159ac7bd41ae427d08d751a30953%7C7ab090d4fa2e4ecfbc7c4127b4d582ec%7C0%7C0%7C637067633428412344&amp;sdata=4TQ2zgaBCAcwtJfcZ0jTMpTHQ2%2FVg7xmV2cZ%2BN5MKBc%3D&amp;reserved=0
>
> Hi,
>
> I read all relevant posts here but did not find one that is related to the question I have, so could you help me?
>
> I was doing jet matching as follows (where H+/H- are the charged components of a real triplet):
> 1. generate p p > H+ H- j
> add process p p > H+ H- j j
> 2. in the run card, I set auto_ptj_mjj to true and some positive number for xqcut.
> 3. I then set ptj=ptb=xqcut with drjj=drbj=drbb=0 as default.
>
> I used MLM matching with CKKW merging and Pythia8 for parton showering. What I found is that, for xqcut<40, the effective luminosity is 0 and the corresponding xsection is infinity. When I set xqcut =40 or 50, the corresponding effective luminosity is O(10^-30~10^-100 pb^-1) with the corresponding xsection being of O(10^30~10^100 pb).
>
> I have been playing with xqcut to get rid of the IR divergence and expect for the xqcut I had been using, the IR divergence shall already be taken care of by Pythia8 so the final result shall be finite. But it turns out the final xsection is divergent. Do you have any suggestion?
>
> I'm using the latest version (v2.6.3.2) of MadGraph.
>
> Thanks and best,
> Yong
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Yong Du (fallive) said : #2

Hi Olivier,

Thank you for the quick reply.

>You can not combine two matching/merging scheme. So either you use MLM or you use CKKW-L. CKKW is not implemented/supported at all in MG5aMC (since it requires additional changes in MG5aMC and that such method is not deprecated in favour of CKKW-L)

Sorry, here what I really meant is I set ktdurham = 1.0 to turn on ktdurham to activate CKKW merging for pythia8. Am I not supposed to do so?

> The first step is to drop the matching/merging and check what is the cross-section of generate p p > H+ H- j and check if this is finite or not.

I did checked that and it's finite. That's why I'm thinking it's the matching that caused the soft and/or the collinear divergence.

> Question for you here, why do not you start at generate p p > H+ H-. Is this process does not exist? Or should you request very hard cut on the jet (much harder than qcut)

Thank you for the question. We require a jet (actually an ISR jet in our case) in our final state just to increase our trigger efficiency, that is why we start at "p p > H+ H- j" instead of "p p > H+ H-".

Best,
Yong

> Sorry, here what I really meant is I set ktdurham = 1.0 to turn on
> ktdurham to activate CKKW merging for pythia8. Am I not supposed to do
> so?

Do you really mean CKKW? or is it CKKW-L?

What is the value of ickkw?
For MLM, you have to set it to one.
For CKKW-L you have to set it to zero
(For CKKW it has to be set to 2 technically but this is deprecated)

With MLM, you typically do not hve any ktdurham cut. I do not say that it is incompatible (but it can, I would have to investigate). In any case if you are in MLM (icckw=1) you CAN NOT use CKKWL in pythia (even less CKKW obviously).

> I did checked that and it's finite. That's why I'm thinking it's the
> matching that caused the soft and/or the collinear divergence.

This means that you have some issue (at parton level) with the cut that you impose.
Likely means that your run_card is not consistent and therefore miss some cut due to that.

> Thank you for the question. We require a jet (actually an ISR jet in our
> case) in our final state just to increase our trigger efficiency, that
> is why we start at "p p > H+ H- j" instead of "p p > H+ H-".

But note that in order to consistently not include it in your generation you should ensure that such jet is NEVER coming from a "p p > H+ H-" generation where the first emission of the parton shower will make that jet included in your analysis (this can happen if your experimental cut on the jet is as hard as your matching scale or softer.

Cheers,

Olivier

> On 15 Oct 2019, at 21:32, Yong Du <email address hidden> wrote:
>
> Question #685196 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/685196
>
> Status: Answered => Open
>
> Yong Du is still having a problem:
> Hi Olivier,
>
> Thank you for the quick reply.
>
>> You can not combine two matching/merging scheme. So either you use MLM
> or you use CKKW-L. CKKW is not implemented/supported at all in MG5aMC
> (since it requires additional changes in MG5aMC and that such method is
> not deprecated in favour of CKKW-L)
>
> Sorry, here what I really meant is I set ktdurham = 1.0 to turn on
> ktdurham to activate CKKW merging for pythia8. Am I not supposed to do
> so?
>
>> The first step is to drop the matching/merging and check what is the
> cross-section of generate p p > H+ H- j and check if this is finite or
> not.
>
> I did checked that and it's finite. That's why I'm thinking it's the
> matching that caused the soft and/or the collinear divergence.
>
>> Question for you here, why do not you start at generate p p > H+ H-.
> Is this process does not exist? Or should you request very hard cut on
> the jet (much harder than qcut)
>
> Thank you for the question. We require a jet (actually an ISR jet in our
> case) in our final state just to increase our trigger efficiency, that
> is why we start at "p p > H+ H- j" instead of "p p > H+ H-".
>
> Best,
> Yong
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Yong Du (fallive) said : #4

Hi Olivier,

Thank you for your quick reply.

I actually set ickkw=1. Based on your comment, it's probably I did not set my run card correctly. I attach the modified part of my run card below, could you kindly check that?

I set ktdurham=1.0 which I thought is relevant for the merging process in Pythia8. But from your comment, it seems usually people do not apply this cut. I will play with it and see what the difference is.

And also plenty of thanks to you for the comment on "p p > H+ H-". For other channels we had considered, we do apply much stronger cuts (typically 100GeV on the pt) than the those in the run card.

Best,
Yong

------------------- Yong run card modified part ----------

#*********************************************************************
 1 = ickkw ! 0 no matching, 1 MLM
 1.0 = alpsfact ! scale factor for QCD emission vx
 False = chcluster ! cluster only according to channel diag
 4 = asrwgtflavor ! highest quark flavor for a_s reweight
 True = auto_ptj_mjj ! Automatic setting of ptj and mjj if xqcut >0
                                   ! (turn off for VBF and single top processes)
 50.0 = xqcut ! minimum kt jet measure between partons
#*********************************************************************
 50.0 = ptj ! minimum pt for the jets
 50.0 = ptb ! minimum pt for the b
#***********************************************************************
 1.0 = ktdurham
#***********************************************************************

Hi,

If you want to use MLM, please set ktdurham to 0.
if you want to use CKKWL then please set ickkw to 0 and xqcut to 0.
(not sure about the pt cut in that case --I have less experience with CKKWL--)

I'm also surprise that you have
4 = asrwgtflavor ! highest quark flavor for a_s reweight
which means that you are doing a 4 flavour matching/merging
but you did specify
50.0 = ptb ! minimum pt for the b
at the same value as ptj
This seems to indicate that you want to do a 5 flavor matching.

If you want to do 5 flavour matching, please set the b-mass to zero at the model level:
see this FAQ:https://answers.launchpad.net/mg5amcnlo/+faq/2312
This might be the issue that can lead to infinities actually.

Cheers,

Olivier

> On 15 Oct 2019, at 22:07, Yong Du <email address hidden> wrote:
>
> Question #685196 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/685196
>
> Status: Answered => Open
>
> Yong Du is still having a problem:
> Hi Olivier,
>
> Thank you for your quick reply.
>
> I actually set ickkw=1. Based on your comment, it's probably I did not
> set my run card correctly. I attach the modified part of my run card
> below, could you kindly check that?
>
> I set ktdurham=1.0 which I thought is relevant for the merging process
> in Pythia8. But from your comment, it seems usually people do not apply
> this cut. I will play with it and see what the difference is.
>
> And also plenty of thanks to you for the comment on "p p > H+ H-". For
> other channels we had considered, we do apply much stronger cuts
> (typically 100GeV on the pt) than the those in the run card.
>
> Best,
> Yong
>
> ------------------- Yong run card modified part ----------
>
> #*********************************************************************
> 1 = ickkw ! 0 no matching, 1 MLM
> 1.0 = alpsfact ! scale factor for QCD emission vx
> False = chcluster ! cluster only according to channel diag
> 4 = asrwgtflavor ! highest quark flavor for a_s reweight
> True = auto_ptj_mjj ! Automatic setting of ptj and mjj if xqcut >0
> ! (turn off for VBF and single top processes)
> 50.0 = xqcut ! minimum kt jet measure between partons
> #*********************************************************************
> 50.0 = ptj ! minimum pt for the jets
> 50.0 = ptb ! minimum pt for the b
> #***********************************************************************
> 1.0 = ktdurham
> #***********************************************************************
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Yong Du (fallive) said : #6

HI Olivier,

In the end, I want to do a 4 flavor jet matching. In my last post, I set ptb =50 for the purpose of debugging as smaller xqcut always give worse divergent result.

Based on your latest suggestion above, I tried many times now by varying ptj, ptb, xqcut, mjj for a 4 flavor jet matching, but still got divergent results. My next plan is to try a 5 flavor jet matching and see what happens. In the meantime, could you please check my run card for the 4 flavor jet matching and let me if my run card settings are consistent?

Thanks a lot and best,
Yong

For the same run card below, I varied xqcut from 20 to 40 and changed the ptj accordingly, but always get divergent result.

------ Yong run card for 4 flavor jet matching ------

#*********************************************************************
# 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 *
# *
# To display more options, you can type the command: *
# update full_run_card *
#*********************************************************************
#
#*******************
# Running parameters
#*******************
#
#*********************************************************************
# Tag name for the run (one word) *
#*********************************************************************
  tag_1 = run_tag ! name of the run
#*********************************************************************
# 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. *
#*********************************************************************
  100 = 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
     6500.0 = ebeam1 ! beam 1 total energy in GeV
     6500.0 = ebeam2 ! beam 2 total energy in GeV
# To see polarised beam options: type "update beam_pol"
#*********************************************************************
# PDF CHOICE: this automatically fixes also alpha_s and its evol. *
#*********************************************************************
     nn23lo1 = pdlabel ! PDF set
     230000 = lhaid ! if pdlabel=lhapdf, this is the lhapdf number
# 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
 91.188 = scale ! fixed ren scale
 91.188 = dsqrt_q2fact1 ! fixed fact scale for pdf1
 91.188 = dsqrt_q2fact2 ! fixed fact scale for pdf2
 -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
 1.0 = scalefact ! scale factor for event-by-event scales
#*********************************************************************
# Type and output format
#*********************************************************************
  False = gridpack !True = setting up the grid pack
  2.25552e-10 = time_of_flight ! threshold (in mm) below which the invariant livetime is not written (-1 means not written)
  3.0 = lhe_version ! Change the way clustering information pass to shower.
  True = clusinfo ! include clustering tag in output
  average = event_norm ! average/sum. Normalization of the weight in the LHEF

#*********************************************************************
# Matching parameter (MLM only)
#*********************************************************************
 1 = ickkw ! 0 no matching, 1 MLM
 1.0 = alpsfact ! scale factor for QCD emission vx
 False = chcluster ! cluster only according to channel diag
 4 = asrwgtflavor ! highest quark flavor for a_s reweight
 True = auto_ptj_mjj ! Automatic setting of ptj and mjj if xqcut >0
                                   ! (turn off for VBF and single top processes)
 40.0 = xqcut ! minimum kt jet measure between partons
#*********************************************************************
#
#*********************************************************************
# handling of the helicities:
# 0: sum over all helicities
# 1: importance sampling over helicities
#*********************************************************************
   0 = nhel ! using helicities importance sampling or not.
#*********************************************************************
# Generation bias, check the wiki page below for more information: *
# 'cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LOEventGenerationBias' *
#*********************************************************************
 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) *
#*********************************************************************
 40.0 = ptj ! minimum pt for the jets
 10.0 = 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
 -1.0 = ptamax ! maximum pt for the photons
 -1.0 = ptlmax ! maximum pt for the charged leptons
 -1.0 = missetmax ! maximum missing Et (sum of neutrino's momenta)
 {} = pt_min_pdg ! pt cut for other particles (use pdg code). Applied on particle and anti-particle
 {} = pt_max_pdg ! pt cut for other particles (syntax e.g. {6: 100, 25: 50})
#*********************************************************************
# 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
  -1.0 = ejmax ! maximum E for the jets
 -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
 {} = e_min_pdg ! E cut for other particles (use pdg code). Applied on particle and anti-particle
 {} = e_max_pdg ! E cut for other particles (syntax e.g. {6: 100, 25: 50})
#*********************************************************************
# 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
 0.0 = etabmin ! min rap for the b
 0.0 = etaamin ! min rap for the photons
 0.0 = etalmin ! main rap for the charged leptons
 {} = eta_min_pdg ! rap cut for other particles (use pdg code). Applied on particle and anti-particle
 {} = eta_max_pdg ! rap cut for other particles (syntax e.g. {6: 2.5, 23: 5})
#*********************************************************************
# Minimum and maximum DeltaR distance *
#*********************************************************************
 0.0 = drjj ! min distance between jets
 0.0 = drbb ! min distance between b's
 0.4 = drll ! min distance between leptons
 0.4 = draa ! min distance between gammas
 0.0 = drbj ! min distance between b and jet
 0.4 = draj ! min distance between gamma and jet
 0.0 = drjl ! min distance between jet and lepton
 0.0 = drab ! min distance between gamma and b
 0.0 = drbl ! min distance between b and lepton
 0.4 = dral ! min distance between gamma and lepton
 -1.0 = drjjmax ! max distance between jets
 -1.0 = drbbmax ! max distance between b's
 -1.0 = drllmax ! max distance between leptons
 -1.0 = draamax ! max distance between gammas
 -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! *
#*********************************************************************
 40.0 = mmjj ! min invariant mass of a jet pair
 10.0 = 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
 -1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
 {} = 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
 0.0 = xptj ! minimum pt for at least one jet
 0.0 = xptb ! minimum pt for at least one b
 0.0 = xpta ! minimum pt for at least one photon
 0.0 = xptl ! minimum pt for at least one charged lepton
#*********************************************************************
# Control the pt's of the jets sorted by pt *
#*********************************************************************
 0.0 = ptj1min ! minimum pt for the leading jet in pt
 0.0 = ptj2min ! minimum pt for the second jet in pt
 0.0 = ptj3min ! minimum pt for the third jet in pt
 0.0 = ptj4min ! minimum pt for the fourth jet in pt
 -1.0 = ptj1max ! maximum pt for the leading jet in pt
 -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
 True = isoEM ! isolate photons from EM energy (photons and leptons)
#*********************************************************************
# 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] *
#***********************************************************************
 0.0 = 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 *
#*********************************************************************
   True = 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'

Yong Du (fallive) said : #7

Hi,

Just to provide more info:

For the pythia8 card, I used:

Main:numberOfEvents = 100
Beams:frameType = 4
HEPMCoutput:file = auto
JetMatching:merge = on
JetMatching:doFxFx = on (divergent result even if I comment out this line)
JetMatching:qCut = 65.0 (divergent result even if I vary it accordingly w.r.t. xqcut in run card)
JetMatching:qCutME = 30.0 (divergent result even if I comment out this line)
JetMatching:setMad = off (divergent result even if I comment out this line)
JetMatching:coneRadius = 0.1 (tested values in range 0.1-2.5, but still got divergent result)
JetMatching:etaJetMax = 10.0
JetMatching:doShowerKt = on
JetMatching:nJetMax = 2
JetMatching:scheme = 1
JetMatching:etaJetMax = 5.0
JetMatching:exclusive = 2

Thanks,
Yong

What is your model?
I would need to test myself to understand what's going on

Cheers,

Olivier

> On 15 Oct 2019, at 21:08, Yong Du <email address hidden> wrote:
>
> New question #685196 on MadGraph5_aMC@NLO:
> https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fanswers.launchpad.net%2Fmg5amcnlo%2F%2Bquestion%2F685196&amp;data=02%7C01%7C%7C6a6f159ac7bd41ae427d08d751a30953%7C7ab090d4fa2e4ecfbc7c4127b4d582ec%7C0%7C0%7C637067633428412344&amp;sdata=4TQ2zgaBCAcwtJfcZ0jTMpTHQ2%2FVg7xmV2cZ%2BN5MKBc%3D&amp;reserved=0
>
> Hi,
>
> I read all relevant posts here but did not find one that is related to the question I have, so could you help me?
>
> I was doing jet matching as follows (where H+/H- are the charged components of a real triplet):
> 1. generate p p > H+ H- j
> add process p p > H+ H- j j
> 2. in the run card, I set auto_ptj_mjj to true and some positive number for xqcut.
> 3. I then set ptj=ptb=xqcut with drjj=drbj=drbb=0 as default.
>
> I used MLM matching with CKKW merging and Pythia8 for parton showering. What I found is that, for xqcut<40, the effective luminosity is 0 and the corresponding xsection is infinity. When I set xqcut =40 or 50, the corresponding effective luminosity is O(10^-30~10^-100 pb^-1) with the corresponding xsection being of O(10^30~10^100 pb).
>
> I have been playing with xqcut to get rid of the IR divergence and expect for the xqcut I had been using, the IR divergence shall already be taken care of by Pythia8 so the final result shall be finite. But it turns out the final xsection is divergent. Do you have any suggestion?
>
> I'm using the latest version (v2.6.3.2) of MadGraph.
>
> Thanks and best,
> Yong
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Yong Du (fallive) said : #9

Hi Olivier,

Thanks for your suggestion on jet matching. I took your last comment as a confirmation on my run card which implied probably there was something wrong with my model. I was to send you the model (the real triplet model) but before that I did more tests in order not to trouble you too much. And then I realized there was some mistakes in my UFO file related to the form factor I applied in my model. After some hard coding to correct that part based on some of the posts here, I now have finite and consistent xsection while varying xqcut even as low as 20 (did not test for lower xqcut). I will test more cases at a later time, but thank you so much for your help!

Best,
Yong