"ERROR: NOT ENOUGH POINTS PASS THE CUTS" when launching VBS at fixed order NLO with cuts in jets

Implementing cuts can destroy the way the phase-space integrator works (even at LO).
If you do implement cuts, you might also need to change the way the phase-space integration is performed
(and the easiest way --if it fit your need -- is to change the set_tau_min to increase the minimal energy of the process)

So did you try to change the phase-space integrator?

Cheers,

Olivier

> On 14 Jun 2021, at 16:50, matteo maltoni <email address hidden> wrote:
>
> New question #697529 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/697529
>
> Dear MadGraph experts,
>
> I'm trying to launch a fixed order generation at NLO for the process (p p > l+ l- j j QCD=0 NP=2 [QCD]). The job works properly, until I add the following cuts:
>
> - Minimum invariant mass for the jets M[jj]>1000 GeV
> - Minimum rapidity difference among the jets |Delta y| [jj]>2
> - Minimum pT for leading and subleading jets at 85 and 80 GeV
>
> The error I find at the end of the log files is:
>
> ERROR: NOT ENOUGH POINTS PASS THE CUTS. RESULTS CANNOT BE TRUSTED. LOOSEN THE GENERATION CUTS, OR ADAPT SET_TAU_MIN() IN SETCUTS.F ACCORDINGLY.
>
> although the same cuts give no problems when I generate events at LO.
> I tried to switch off some of them, but the error occurs anyway.
> This is the way I implemented the cuts in the cuts.f file, just after the call to fastjet:
>
> if(mjj.gt.0d0) then
> if(invm2_04(pjet(0,1),pjet(0,2),1d0).lt.mjj**2) then
> passcuts_user=.false.
> return
> endif
> endif
> if(dyjj.gt.0d0) then
> if(getdrapv4(pjet(0,1),pjet(0,2)).lt.dyjj) then
> passcuts_user=.false.
> return
> endif
> endif
> if(ptj1min.gt.0d0 .and. pt_04(pjet(0,1)).lt.ptj1min) then
> passcuts_user=.false.
> return
> endif
> if(ptj2min.gt.0d0 .and. pt_04(pjet(0,2)).lt.ptj2min) then
> passcuts_user=.false.
> return
> endif
>
> Do you have any possible solution?
> I attach the run_card below.
>
> Thank you,
>
> Matteo
>
>
> #*******************
> # Running parameters
> #*******************
> #
> #***********************************************************************
> # Tag name for the run (one word) *
> #***********************************************************************
> tag_1 = run_tag ! name of the run
> #***********************************************************************
> # Number of LHE events (and their normalization) and the required *
> # (relative) accuracy on the Xsec. *
> # These values are ignored for fixed order runs *
> #***********************************************************************
> 10000 = nevents ! Number of unweighted events requested
> -1.0 = req_acc ! Required accuracy (-1=auto determined from nevents)
> -1 = nevt_job! Max number of events per job in event generation.
> ! (-1= no split).
> #***********************************************************************
> # Normalize the weights of LHE events such that they sum or average to *
> # the total cross section *
> #***********************************************************************
> average = event_norm ! valid settings: average, sum, bias
> #***********************************************************************
> # Number of points per itegration channel (ignored for aMC@NLO runs) *
> #***********************************************************************
> 0.005 = req_acc_FO ! Required accuracy (-1=ignored, and use the
> ! number of points and iter. below)
> # These numbers are ignored except if req_acc_FO is equal to -1
> 5000 = npoints_FO_grid ! number of points to setup grids
> 4 = niters_FO_grid ! number of iter. to setup grids
> 10000 = npoints_FO ! number of points to compute Xsec
> 6 = niters_FO ! number of iter. to compute Xsec
> #***********************************************************************
> # Random number seed *
> #***********************************************************************
> 0 = iseed ! rnd seed (0=assigned automatically=default))
> #***********************************************************************
> # Collider type and energy *
> #***********************************************************************
> 1 = lpp1 ! beam 1 type (0 = no PDF)
> 1 = lpp2 ! beam 2 type (0 = no PDF)
> 6500.0 = ebeam1 ! beam 1 energy in GeV
> 6500.0 = ebeam2 ! beam 2 energy in GeV
> #***********************************************************************
> # PDF choice: this automatically fixes also alpha_s(MZ) and its evol. *
> #***********************************************************************
> nn23nlo = pdlabel ! PDF set
> 244600 = lhaid ! If pdlabel=lhapdf, this is the lhapdf number. Only
> ! numbers for central PDF sets are allowed. Can be a list;
> ! PDF sets beyond the first are included via reweighting.
> #***********************************************************************
> # Include the NLO Monte Carlo subtr. terms for the following parton *
> # shower (HERWIG6 | HERWIGPP | PYTHIA6Q | PYTHIA6PT | PYTHIA8) *
> # WARNING: PYTHIA6PT works only for processes without FSR!!!! *
> #***********************************************************************
> HERWIG6 = parton_shower
> 1.0 = shower_scale_factor ! multiply default shower starting
> ! scale by this factor
> #***********************************************************************
> # Renormalization and factorization scales *
> # (Default functional form for the non-fixed scales is the sum of *
> # the transverse masses divided by two of all final state particles *
> # and partons. This can be changed in SubProcesses/set_scales.f or via *
> # dynamical_scale_choice option) *
> #***********************************************************************
> False = fixed_ren_scale ! if .true. use fixed ren scale
> False = fixed_fac_scale ! if .true. use fixed fac scale
> 91.118 = muR_ref_fixed ! fixed ren reference scale
> 91.118 = muF_ref_fixed ! fixed fact reference scale
> -1 = dynamical_scale_choice ! Choose one (or more) of the predefined
> ! dynamical choices. Can be a list; scale choices beyond the
> ! first are included via reweighting
> 1.0 = muR_over_ref ! ratio of current muR over reference muR
> 1.0 = muF_over_ref ! ratio of current muF over reference muF
> #***********************************************************************
> # Reweight variables for scale dependence and PDF uncertainty *
> #***********************************************************************
> 1.0, 2.0, 0.5 = rw_rscale ! muR factors to be included by reweighting
> 1.0, 2.0, 0.5 = rw_fscale ! muF factors to be included by reweighting
> True = reweight_scale ! Reweight to get scale variation using the
> ! rw_rscale and rw_fscale factors. Should be a list of
> ! booleans of equal length to dynamical_scale_choice to
> ! specify for which choice to include scale dependence.
> False = reweight_PDF ! Reweight to get PDF uncertainty. Should be a
> ! list booleans of equal length to lhaid to specify for
> ! which PDF set to include the uncertainties.
> #***********************************************************************
> # Store reweight information in the LHE file for off-line model- *
> # parameter reweighting at NLO+PS accuracy *
> #***********************************************************************
> False = store_rwgt_info ! Store info for reweighting in LHE file
> #***********************************************************************
> # ickkw parameter: *
> # 0: No merging *
> # 3: FxFx Merging - WARNING! Applies merging only at the hard-event *
> # level. After showering an MLM-type merging should be applied as *
> # well. See http://amcatnlo.cern.ch/FxFx_merging.htm for details. *
> # 4: UNLOPS merging (with pythia8 only). No interface from within *
> # MG5_aMC available, but available in Pythia8. *
> # -1: NNLL+NLO jet-veto computation. See arxiv:1412.8408 [hep-ph]. *
> #***********************************************************************
> 0 = ickkw
> #***********************************************************************
> #
> #***********************************************************************
> # BW cutoff (M+/-bwcutoff*Gamma). Determines which resonances are *
> # written in the LHE event file *
> #***********************************************************************
> 15.0 = bwcutoff
> #***********************************************************************
> # Cuts on the jets. Jet clustering is performed by FastJet. *
> # - If gamma_is_j, photons are also clustered *
> # - When matching to a parton shower, these generation cuts should be *
> # considerably softer than the analysis cuts. *
> # - More specific cuts can be specified in SubProcesses/cuts.f *
> #***********************************************************************
> -1.0 = jetalgo ! FastJet jet algorithm (1=kT, 0=C/A, -1=anti-kT)
> 0.4 = jetradius ! The radius parameter for the jet algorithm
> 25.0 = ptj ! Min jet transverse momentum
> 5.0 = etaj ! Max jet abs(pseudo-rap) (a value .lt.0 means no cut)
> 4.4 = yjmax
> True = gamma_is_j! Wether to cluster photons as jets or not
> 1000.0 = mjj
> 2.0 = dyjj
> 85.0 = ptj1min
> 80.0 = ptj2min
> #***********************************************************************
> # Cuts on the charged leptons (e+, e-, mu+, mu-, tau+ and tau-) *
> # More specific cuts can be specified in SubProcesses/cuts.f *
> #***********************************************************************
> 25.0 = ptl ! Min lepton transverse momentum
> 2.4 = etal ! Max lepton abs(pseudo-rap) (a value .lt.0 means no cut)
> 0.0 = drll ! Min distance between opposite sign lepton pairs
> 0.0 = drll_sf ! Min distance between opp. sign same-flavor lepton pairs
> 0.0 = mll ! Min inv. mass of all opposite sign lepton pairs
> 81.2 = mll_sf ! Min inv. mass of all opp. sign same-flavor lepton pairs
> 101.2 = mll_max_sf
> 20.0 = ptll
> 0.4 = drjl
> #***********************************************************************
> # Fermion-photon recombination parameters *
> # If Rphreco=0, no recombination is performed *
> #***********************************************************************
> 0.1 = Rphreco ! Minimum fermion-photon distance for recombination
> -1.0 = etaphreco ! Maximum abs(pseudo-rap) for photons to be recombined (a value .lt.0 means no cut)
> True = lepphreco ! Recombine photons and leptons together
> True = quarkphreco ! Recombine photons and quarks together
> #***********************************************************************
> # Photon-isolation cuts, according to hep-ph/9801442 *
> # Not applied if gamma_is_j *
> # When ptgmin=0, all the other parameters are ignored *
> # More specific cuts can be specified in SubProcesses/cuts.f *
> #***********************************************************************
> 20.0 = ptgmin ! Min photon transverse momentum
> -1.0 = etagamma ! Max photon abs(pseudo-rap)
> 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)
> #***********************************************************************
> # Cuts associated to MASSIVE particles identified by their PDG codes. *
> # All cuts are applied to both particles and anti-particles, so use *
> # POSITIVE PDG CODES only. Example of the syntax is {6 : 100} or *
> # {6:100, 25:200} for multiple particles *
> #***********************************************************************
> {} = pt_min_pdg ! Min pT for a massive particle
> {} = pt_max_pdg ! Max pT for a massive particle
> {} = mxx_min_pdg ! inv. mass for any pair of (anti)particles
> #***********************************************************************
> # Use PineAPPL to generate PDF-independent fast-interpolation grid *
> # (https://zenodo.org/record/3992765#.X2EWy5MzbVo) *
> #***********************************************************************
> False = pineappl ! PineAPPL switch
> #***********************************************************************
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier,

Thank you for your prompt answer.
I did not try to change the integrator, because the cuts are working at LO.

Should I try to change one of these values:

            taumin(iFKS,ichan)=0.d0
            taumin_s(iFKS,ichan)=0.d0
            taumin_j(iFKS,ichan)=0.d0

 at line 260 of the setcuts.f file? To which value?

Best,

Matteo

Maybe you can start by reading this thread:
https://answers.launchpad.net/mg5amcnlo/+question/446723

If this is not enough then we will need to ask someone more expert than me in NLO computation.

Cheers,

Olivier

Dear Olivier,

Thank you for the link, it's been extremely useful.
I managed to fix the cuts on the pTs of the leading and subleading jets, by setting taumin_j(iFKS,ichan), at line 262, to the value 85+80+20=185 GeV, since I also implemented a cut on pT[ll] > 20 GeV.

Unluckily, when I try to add the cut on M[jj], by setting taumin_j(iFKS,ichan) to values higher than

sqrt(85**2 + (1000/2)**2) + sqrt(80**2 + (1000/2)**2) + 20 = 1033.5 GeV

I still get the same error. I have two questions about this:

1) In the thread you sent me, Rikkert claims the problem is the related to EW loop corrections missing in the VBF generation; is that issue solved in v3.1?

2) I bypassed the problem by adding the cut on M[jj] in the analysis_HwU.f file, in the part in which the histograms are filled, by adding the line

if(mjj.lt.1d3) cycle

Do you know if there's a way to know how much cross-section I loose by imposing this cut there, with respect to the final result given by MadGraph?

Best,

Matteo

Thanks Rikkert Frederix, that solved my question.