Z+3jets production with merging

Hi Adam,

This should be linked that you are hitting a LO singularities (i.e. that a part of the phase-space that you allow within your cut is extremely sensitive to higher order correction).
Such singularities make the event generation not reliable (in top that most of the events are generated in the unphysical part of the phase-space).

Cheers,

Olivier

On Sep 3, 2014, at 2:03 PM, Adam Alloul <email address hidden> wrote:

> New question #254014 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/254014
>
> Dear Madgraph authors,
>
> my collaborators and I have been trying to generate Z+3jets for low mll values and we did not succeed so far to get the gridpack to produce the number of events we require. Below are some details.
>
> we define
> l+ = e+ mu+ ta+
> l- = e- mu- ta-
> j = u u~ c c~ d d~ s s~ g b b~
> p = j
> we import the model sm-no_masses
> we generate exclusively:
> p p > l+ l- j j j / h @11
>
> with the following run_card.dat
>
> #*********************************************************************
> # 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 *
> #*********************************************************************
> .true. = 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 *
> #*********************************************************************
> 25 = 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
>
> After producing the gridpack, we ask for 100k events and cannot get more than 16k. We even got an LHE with 3000 events. We have also tried to put extra cuts on the minimum pT of the photon, the draa variable and the dral variable but this didn't help. We are also facing the same problem for an invariant mass of the dilepton system larger than 50GeV.
>
> Could you please help us with this issue ?
>
> Thank you in advance,
>
> Adam.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

thank you for your very quick answer!

That's what I was thinking but I was wondering if you had an idea of which cut we should enable or tighten to avoid these singularities?

Hi,

I guess that you should play with drll and mmll.
I would suggest that you look at the plot of those variable they often indicate at which value you start to be in the unphysical area.

Cheers,

Olivier

On Sep 3, 2014, at 2:33 PM, Adam Alloul <email address hidden> wrote:

> Question #254014 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/254014
>
> Status: Answered => Open
>
> Adam Alloul is still having a problem:
> Hi Olivier,
>
> thank you for your very quick answer!
>
> That's what I was thinking but I was wondering if you had an idea of
> which cut we should enable or tighten to avoid these singularities?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

just to let you know that the drll variable was indeed the one causing us trouble (keeping in mind that 10 < mll < 50). Varying its value, we have found that we avoid the divergencies for a minimum value around 0.15. However neither DRLL nor mll plots for the "faulty' values help as the distributions do not exhibit any "weird" behaviour. I guess that MG5 does not write the events with divergencies.

If you allow me, I would like just to ask you whether this result is expected to you?

Thanks a lot!

Adam.