ttbar signal events confirmation

Asked by krunal on 2017-08-18

Hi,

I wanted to confirm that are the following commands correct for generating ttbar signal (p p >t t~) decaying through leptonic, semi-leptonic and hadronic channels: (I am copying a part of proc_card here)

import model sm
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
define pp = d s
define jj = u~ c~
define ppp = d~ s~
define jjj = u c
define ll+ = e+ mu+ ta+
define ll- = e- mu- ta-
generate p p > t t~, (t > w+ b, w+ > ll+ vl), (t~ > w- b~, w- > ll- vl~)
add process p p > t t~, (t > w+ b, w+ > ppp jjj), (t~ > w- b~, w- > pp jj)
add process p p > t t~, (t > w+ b, w+ > ppp jjj), (t~ > w- b~, w- > ll- vl~)
add process p p > t t~, (t > w+ b, w+ > ll+ vl), (t~ > w- b~, w- > pp jj)
output ttbar_f

Please let me know if there are issues with these commands. Are the final events generated taking the appropriate branching ratios into account or should I generate each decay channel separately?

Thanking you
Krunal

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2017-09-03
Last query:
2017-09-03
Last reply:
2017-08-19

This question was reopened

Hi,

Since you want all of them, I would have done:
define wdec = j e+ mu+ ta+ e- mu- ta- ve vm vt ve~ vm~ vt~
generate p p > t t~, (t > w+ b, w+ > wdec wdec), (t~ > w- b~, w- > wdec wdec)
which might result in a more optimal code for the generation.
But your syntax has nothing wrong in itself.

Please let me know if there are issues with these commands. Are the final events generated taking the appropriate branching ratios into account or should I generate each decay channel separately?

Note that we do not use Branching ratio in our computation. So we compute the cross-section for each process and the number of events of each process is proportional to the evaluated cross-section. (So in some sense the Branching ratio is computed on the flight). This might be problematic if you do not want to use the LO branching ratio. In that particular case, you would be force to generate each sample independently (or you use other method like MadSpin)

Cheers,

Olivier

krunal (krunal94) said : #2

Hi Olivier,

Thank you for the reply.

Also, I wanted to confirm that the "effective luminosity" means " integrated luminosity". Right? And the value of effective luminosity gets displayed when the events are generated. Is there any other place in the folder where they get recorded so that I could access them again in future?

KInd regards
Krunal

krunal (krunal94) said : #3

Thanks Olivier Mattelaer, that solved my question.

Hi,

The effective luminosity is a debug information and not a physical information. Those are only printed inside the html page and should only be use for debugging.

For each channel of integration, we generate a given number of events. Those events correspond to a given cross-section and therefore
to an integrated luminosity. When we combine two channel, the integrated luminosity of the two sample is equal to the minimum of those integrated luminosity.
So the final sample that you get has a single unique luminosity.

Cheers,

Olivier

> On 18 Aug 2017, at 18:09, krunal <email address hidden> wrote:
>
> Question #656508 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/656508
>
> krunal posted a new comment:
> Hi Olivier,
>
> Thank you for the reply.
>
> Also, I wanted to confirm that the "effective luminosity" means "
> integrated luminosity". Right? And the value of effective luminosity
> gets displayed when the events are generated. Is there any other place
> in the folder where they get recorded so that I could access them again
> in future?
>
> KInd regards
> Krunal
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

krunal (krunal94) said : #5

Hi Olivier,

Thank you for the reply.

Is there any place I could find that unique luminosity for my processes. I want to compare this MC data with real data. Suppose the real data has integrated luminosity of 50/pb. So I thought that I would change the weight of the events so as to achieve a similar value of luminosity.(I mean that since cross section and luminosity is fixed, I'll fix the number of events too and then only change the weight of the events to compare them to real data in a way that both these data sets have same integrated luminosity.)

Kind regards,
Krunal

Hi,

It is not written anywhere. However, you can actually compute it very easily since you have the cross-section and the number of events generated.
So you just have to divide those two number to have the luminosity.

Cheers,

Olivier

> On 18 Aug 2017, at 18:38, krunal <email address hidden> wrote:
>
> Question #656508 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/656508
>
> krunal posted a new comment:
> Hi Olivier,
>
> Thank you for the reply.
>
> Is there any place I could find that unique luminosity for my processes.
> I want to compare this MC data with real data. Suppose the real data has
> integrated luminosity of 50/pb. So I thought that I would change the
> weight of the events so as to achieve a similar value of luminosity.(I
> mean that since cross section and luminosity is fixed, I'll fix the
> number of events too and then only change the weight of the events to
> compare them to real data in a way that both these data sets have same
> integrated luminosity.)
>
> Kind regards,
> Krunal
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

krunal (krunal94) said : #7

Hi,

Ohh.. Sure :)

Thank you for the reply.

Kind regards,
Krunal

krunal (krunal94) said : #8

Hi Olivier,

I tried to generate the events for the process I listed above (signal ttbar) using Pythia8 interface of MG5. To avoid avoid double counting of jets, I tried to learn a bit about matching of jets and wanted to confirm that are the following changes enough in the run_card (as I faced an error while generating the events :

----------------------------------------------------------------------------------------------------------------------
Merging results from the split PY8 runs...
INFO: Create matching plots for Pythia8
Command "generate_events run_02" interrupted with error:
IndexError : list index out of range
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in '/home/krunal/Downloads/MG5_aMC_v2_5_4/ttbar_f/run_02_tag_1_debug.log'.
Please attach this file to your report.
INFO: storing files of previous run
INFO: Done
)
-------------------------------------------------------------------------------------------------------------------
Following are the changes in made to the run_card for jet matching: (part of run_card pasted)

#*********************************************************************
# 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)
 20.0 = xqcut ! minimum kt jet measure between partons

#*********************************************************************
# 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

#*********************************************************************
# 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

I KEPT THE FOLLOWING UNCHANGED:

#***********************************************************************
# Turn on either the ktdurham or ptlund cut to activate *
# CKKW(L) merging with Pythia8 [arXiv:1410.3012, arXiv:1109.4829] *
#***********************************************************************
 -1.0 = ktdurham
 0.4 = dparameter
 -1.0 = ptlund
 1, 2, 3, 4, 5, 6, 21 = pdgs_for_merging_cut ! PDGs for two cuts above

------------------------------------------------------------------------------------------------------------------------------------------------

I kept the pythia_card unchanged.

KInd regards,
Krunal

Dear Kunal,

If you use the above syntax, I do not see the point of doing matching/merging.
Other than that your syntax is correct. I believe that such error is actually already solved in 2.6.0

Cheers,

Olivier

krunal (krunal94) said : #10

Thanks Olivier Mattelaer, that solved my question.