0 jet/extra jet events in b jet analysis?

Asked by Billy Ford on 2019-01-22

Hi,

I am using Madgraph5 + Pythia8 to generate data samples of 2HDM Higgs' decaying into 4 b's, and investigating the jet multiplicity distributions to look at boosted jet merging.

My toolkit currently runs MG5 and Pythia8 to produce the hepmc event file, which I then feed into MadAnalysis. When I do this and observe my multiplicity distribution, I seem to be getting a small number of events (~5% altogether) containing 0 b jets, and some with 5 or 6 b jets (despite specifying the process as pp > H, and forcing this to decay to two lighter Higgs' which each in turn decay to a b b~ pair, so there should only be up to 4 b's in the final state and hence 4 b-tagged jets?).

I have removed all cuts on the b jets for the time being, and set main.fastsim.bjet_id.exclusive = true to try and prevent over counting. Might you have any idea where these events with N(b jets) > 4 and = 0 be coming from?

As a note doing the same for a SM Higgs into b b~, I see a similar number of 3/4 jet events (above the expected 2), but no 0 jet events in this case.

Thanks,
Billy

Question information

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MadAnalysis 5 Edit question
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Last query:
2019-01-22
Last reply:
2019-01-24
Benjamin Fuks (fuks) said : #1

Hi Billy,

I am not surprized by your findings, as extra radiation can come from parton showering (I assumed you set a 100% b-tagging efficiency), and som b-jets may lie outside the acceptance. What would be good is to get the event id for which those events arise and check into the hepmc file what is going on.

Cheers,

Benjamin

> On 22 Jan 2019, at 15:13 , Billy Ford <email address hidden> wrote:
>
> New question #677992 on MadAnalysis 5:
> https://answers.launchpad.net/madanalysis5/+question/677992
>
> Hi,
>
> I am using Madgraph5 + Pythia8 to generate data samples of 2HDM Higgs' decaying into 4 b's, and investigating the jet multiplicity distributions to look at boosted jet merging.
>
> My toolkit currently runs MG5 and Pythia8 to produce the hepmc event file, which I then feed into MadAnalysis. When I do this and observe my multiplicity distribution, I seem to be getting a small number of events (~5% altogether) containing 0 b jets, and some with 5 or 6 b jets (despite specifying the process as pp > H, and forcing this to decay to two lighter Higgs' which each in turn decay to a b b~ pair, so there should only be up to 4 b's in the final state and hence 4 b-tagged jets?).
>
> I have removed all cuts on the b jets for the time being, and set main.fastsim.bjet_id.exclusive = true to try and prevent over counting. Might you have any idea where these events with N(b jets) > 4 and = 0 be coming from?
>
> As a note doing the same for a SM Higgs into b b~, I see a similar number of 3/4 jet events (above the expected 2), but no 0 jet events in this case.
>
> Thanks,
> Billy
>
> --
> You received this question notification because you are an answer
> contact for MadAnalysis 5.

Billy Ford (billyford) said : #2

Benjamin,

The b-tagging efficiency is indeed 100%, and c/l-misid is 0.

Just as a sanity check, my understanding of the b-tagging routine is that we check whether the jet lies within a cone of radius R (set by the jet_id.matching_dr parameter) of the b in the partonic event, so 100% would mean all jets satisfying this criteria are tagged as b's, BUT not all b-jets will necessarily satisfy this criteria depending on the input radius?

Also as a test it would be nice to be able to see the exact number of events in each b-jet multiplicity bin rather than having to read off of the histograms. I wonder if this is possible, as I haven't been able to find the syntax to do so? Likewise for event id's of certain events.

Cheers,
Billy

Benjamin Fuks (fuks) said : #3

Hi Billy,

> Just as a sanity check, my understanding of the b-tagging routine is
> that we check whether the jet lies within a cone of radius R (set by the
> jet_id.matching_dr parameter) of the b in the partonic event, so 100%
> would mean all jets satisfying this criteria are tagged as b's, BUT not
> all b-jets will necessarily satisfy this criteria depending on the input
> radius?

All b-tagged jets satisfy the criterion as there is no mistagging rate.

>
> Also as a test it would be nice to be able to see the exact number of
> events in each b-jet multiplicity bin rather than having to read off of
> the histograms. I wonder if this is possible, as I haven't been able to
> find the syntax to do so? Likewise for event id's of certain events.
The text output is available from the working directory. You can also simulate a smaller event sample and check the files with your eyes.

Cheers,

Benjamin

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