Inconsistency on the number of events

Hi,

Here I'm confused about the b mass.
From the model, I do see that this is a four flavour model.
But it seems that you force it to behave like a five flavour model.
Is this correct?

Otherwise the only parameter really weird in your generation is the fact that you use a quite large value for
bwcutoff. 30 starts to be a quite large value and might be the reason of your discripancy in the rate of Z in the second generation.

Normally the recomend way to generate background versus resonances is to use
generate p p > b b~ part QED=2 $ Z
but the fact that "part" can be a b/b~ might lead to some issue with the NWA that would invalidates your syntax.
Did you check that? (one way is to do your comparison in four flavour first to avoid that issue)

Cheers,

Olivier

> On 17 Feb 2022, at 16:50, Laura Buonincontri <email address hidden> wrote:
>
> New question #700655 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/700655
>
> Dear Olivier,
>
> I am trying to produce Monte Carlo events for LHCb (2<eta<5) with madgraph for the signal (Z+jet), where the Z decay in b pairs, and the background.
> I am writing because I found some inconsistencies in the number of Z events I found in the two cases.
> I copied the run_card.dat for the signal below this question. The run_card for the background is identical. As you will see I put some cuts on the final jets pt, and on the invariant mass (restricted to [70,200] GeV).
>
> I report here the generation commands for the signal:
>
> MG5_aMC> import model heft-full
> MG5_aMC> define p = p b b~
> MG5_aMC> define part = g a u d s c b u~ d~ s~ c~ b~
> MG5_aMC> generate p p > z part QED=2, z > b b~
>
> I found a cross section of 49.65 +- 0.2901 pb. I generated 200000 events. If I calculate the number of Z events for an integrated luminosity of L= 6000 pb^-1 I find around 297000 events.
>
>
> For what concern the background, the commands I typed are:
>
> MG5_aMC> import model heft-full
> MG5_aMC> define p = p b b~
> MG5_aMC> define part = g a u d s c b u~ d~ s~ c~ b~
> MG5_aMC> generate p p > b b~ part QED=2
>
> I found a cross section of 4176 +- 15 pb. I generated 200000 events. And here I found the inconsistency: in the background I found 763 events that contain the Z. That means, for an integrated luminosity of L= 6000 pb^-1, around 95590 events. This means that in the background I find 3 times less Z events with respect to the signal.
> Maybe I am doing some stupid errors, but since the two run_card.dat are identical, I can't explain this difference.
>
>
> I also noticed another thing.
> I generated again the signal, with the same commands as before, with the same run_card as before, where I only removed the cut on the invariant mass [70,200] putting the mmjj, mmjjmax, mmbb, mmbbmax, to 0,-1,0,-1 respectively.
> I found a cross section of 809.2 ± 5.2 pb. I generated 200000 events. The number of events with the Z invariant mass in the interval [70,200] is 195978, that means, for an integrated luminosity of L= 6000 pb^-1, around 4760600 events. That is too much with respect to both the previous samples.
>
> Could you help me to understand what I am doing wrong?
>
> Thank you,
>
> Laura Buonincontri
>
>
> #*********************************************************************
> # 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 *
> #*********************************************************************
> #
> #*********************************************************************
> # 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 *
> #*********************************************************************
> 10000 = 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, 4=photon from muon *
> #*********************************************************************
> 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
> #*********************************************************************
> True = gridpack !True = setting up the grid pack
> -1.0 = time_of_flight ! threshold (in mm) below which the invariant livetime is not written (-1 means not written)
> average = event_norm ! average/sum. Normalization of the weight in the LHEF
> # To see MLM/CKKW merging options: type "update MLM" or "update CKKW"
>
> #*********************************************************************
> #
> #*********************************************************************
> # Phase-Space Optimization strategy (basic options)
> #*********************************************************************
> 0 = nhel ! using helicities importance sampling or not.
> ! 0: sum over helicity, 1: importance sampling
> 1 = sde_strategy ! default integration strategy (hep-ph/2021.xxxxx)
> ! 1 is old strategy (using amp square)
> ! 2 is new strategy (using only the denominator)
> # To see advanced option for Phase-Space optimization: type "update psoptim"
> #*********************************************************************
> # 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
> #*********************************************************************
> 30.0 = 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)
> #*********************************************************************
> True = cut_decays ! Cut decay products
> #*********************************************************************
> # Standard Cuts *
> #*********************************************************************
> # Minimum and maximum pt's (for max, -1 means no cut) *
> #*********************************************************************
> 5.0 = ptj ! minimum pt for the jets
> 5.0 = pta ! minimum pt for the photons
> -1.0 = ptjmax ! maximum pt for the jets
> -1.0 = ptamax ! maximum pt for the photons
> {} = 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})
> #
> # For display option for energy cut in the partonic center of mass frame type 'update ecut'
> #
> #*********************************************************************
> # Maximum and minimum absolute rapidity (for max, -1 means no cut) *
> #*********************************************************************
> 5.0 = etaj ! max rap for the jets
> 5.0 = etaa ! max rap for the photons
> 2.0 = etajmin ! min rap for the jets
> 2.0 = etaamin ! min rap for the photons
> {} = 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 = draj ! min distance between gamma and jet
> -1.0 = drjjmax ! max distance between jets
> -1.0 = drajmax ! max distance between gamma and jet
> #*********************************************************************
> # Minimum and maximum invariant mass for pairs *
> #*********************************************************************
> 70.0 = mmjj ! min invariant mass of a jet pair
> 200.0 = mmjjmax ! max invariant mass of a jet 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.
> #*********************************************************************
> # Inclusive cuts *
> #*********************************************************************
> 0.0 = xptj ! minimum pt for at least one jet
> #*********************************************************************
> # 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
> -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
> 0 = cutuse ! reject event if fails any (0) / all (1) jet pt cuts
> #*********************************************************************
> # 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
> -1.0 = ht2max ! maximum Ht for the two leading jets
> -1.0 = ht3max ! maximum Ht for the three 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
> 0.0 = 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
> #*********************************************************************
> # maximal pdg code for quark to be considered as a light jet *
> # (otherwise b cuts are applied) *
> #*********************************************************************
> 5 = 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'#*********************************************************************
> # Additional hidden parameters
> #*********************************************************************
> 70.0 = mmbb # hidden_parameter
> 2.0 = etabmin # hidden_parameter
> 5.0 = ptb # hidden_parameter
> 200.0 = mmbbmax # hidden_parameter
> 5.0 = etab # hidden_parameter
>
>
>
> --
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Dear Olivier,
Thank you for your answer.
Well, I don't force anything. If you are referring to the maxjetflavor parameter , it is set to 5 automatically with the generation commands I wrote in the question.
However, what would be the consequences of the fact that it is a five flavour model?

For what concern the bwcutoff, I think that it is better if I explain what I am trying to do.
I want to have an estimate of the number of Z to bb, and QCD events that I may found in the Higgs mass region (for example between 100 GeV and 150 GeV). The bwcutoff set to 15 means that the onshell region for the Z goes from 54 GeV to 126 GeV. Outside that range the Z are not generated. So, I put the bwcutoff to 30 in all the run_card of the three generations to extend the Z mass region.
Maybe it was not the best idea, I am quite new in madgraph!

With the background generation that you suggested I would only have the off-shell Z, so, with a bwcutoff set to 15, I will have Z events only from 126 GeV and below 54 GeV.

I think that, on the basis of what you answered me, the best option for my specific analysis is try to generate the background using generate p p > b b~ part QED=2 $$ Z, so I can have the number of QCD background events without the Z; and generate the signal with the command p p > z > b b~ part, in which there are no on/off-shell cuts.

However, the fact that the signal contribution generated together with the background is non compatible with the signal only generation, worries me and with the above mentioned solution I cannot check it.

I will try to understand and check your suggestion about the NWA approximation.

Best regards,

Laura Buonincontri

Hi,

Let first simplify the problem to a fully consistent four flavour and really force to have only QED interaction (I guess part of your problem is also that you have QCD part).

When studying that process, you realize that you have two source of Z onshell (and therefore two source of Z written in the event file).
I have run the following command:

import model heft
#define p = p b b~
define part = g a u d s c b u~ d~ s~ c~ b~
define part = part / b b~
define p = p / g
generate p p > z part QCD=0, z > b b~
add process p p > b b~ part QCD=0 $ z
add process p p > b b~ part QCD=0
add process p p > z , z > b b~ a
output
launch
set nevents 50k
set sde_strategy 1 # I prefer that strategy when using $ syntax but this is not required
set cut_decays True

The results for the four cross-section are:

Graph Cross-Section ↓ Error Events (K) Unwgt Luminosity
P1_qq_za_z_bbx 10.2
P2_qq_bbxa 0.4952
P3_qq_bbxa 16.97
P4_qq_z_z_bbxa 6.281

So I guess that this is your issue (onshell Z decaying into three particles)

After agreeing on that, then you can start to add QCD, and if you want check if it works in five flavor as well.

Cheers,

Olivier