Extract information from Fastjet

Dear Olympia,

if I understand your question correctly, you want a code
that combines the light partons into jets through fastjet.

Examples of such codes (in fortran) are for instance in
FixedOrderAnalysis/analysis_HwU_pp_tj.f
where at lines 117 to 212 you can find the definition of
particles to be clustered, the call to fastjet, the definition
of some observables with jet momenta.
This code works if you are doing fixed-order NLO simulation.
For NLO matching to parton shower, please refer to the
analogous code
MCatNLO/HWAnalyzer/vim mcatnlo_hwan_pp_tj.f

In general, the fastjet routines that perform the clustering
can be found in
MCatNLO/srcCommon/myfastjetfortran.cc,
SubProcesses/fastjetfortran_madfks_full.f
or similar.

Cheers,
Paolo

Hi Paolo,

 the process that I generate is p p > y > z z , z > mu+ mu- , z > d d~ y, d > j , d~ > j. After the parton shower-hadronization I convert the .hep file into a .root file, from which I create a class ( .C and .h). In this file I write my code, so I have already take kinematic information from the d-quarks and the muons ( I calculate the invariant mass,etc.) but I have problem with the jets, I don't understand how to take the same informations from the jets. So I ask for fastjet because as far as I understand I can calculate the ΔR between them and their pT???

 I hope that this make it more clear to you.

Thanks,
Olympia.

Dear Olympia,

the fastjet routines (like the one I mentioned before) take all partons
(or whatever particle you tell them) in the shower output, cluster them
into jets, and assign a four-momentum to each jet.
Namely the main output of the fastjet routines is the set of momenta of
the jets, that you can use to build your observables (like DeltaR etc.).

So if you have the parton momenta out of the shower, you just need to feed
the fastjet routines with this momenta, and get the jet momenta as output.

I don’t know the details of how to link the fastjet routines in your class,
because these details are specific to your class, but the fastjet documentation
should be of help in this.

Note also that in principle one should cluster hadrons rather than partons,
so I would just feed fastjet with the set of hadron momenta that come out
of the shower.

Cheers.
Paolo

On 28 Jan 2016, at 16:12, Olympia <email address hidden> wrote:

> Question #283840 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/283840
>
> Olympia posted a new comment:
> Hi Paolo,
>
> the process that I generate is p p > y > z z , z > mu+ mu- , z > d d~
> y, d > j , d~ > j. After the parton shower-hadronization I convert the
> .hep file into a .root file, from which I create a class ( .C and .h).
> In this file I write my code, so I have already take kinematic
> information from the d-quarks and the muons ( I calculate the invariant
> mass,etc.) but I have problem with the jets, I don't understand how to
> take the same informations from the jets. So I ask for fastjet because
> as far as I understand I can calculate the ΔR between them and their
> pT???
>
> I hope that this make it more clear to you.
>
> Thanks,
> Olympia.
>
> --
> You received this question notification because you are subscribed to
> the question.

Thanks Paolo! It became more clear now.

Olympia.