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The EMCAL core framework

The EMCAL framework consists of

Writing an analysis using the AliAnalysisTaskEmcal

The core of the EMCAL core framework is the AliAnalysisTaskEmcal. It should be used for EMCAL or jet related analyses. The AliAnalysisTaskEmcal

  • Handles cluster-/particle-/track-containers (see below)
  • Performs event selection
  • Fills QA histograms
  • Runs the user code

In order to run the user code, users have to implement either of the two functions:

  • bool FillHistograms()
  • bool Run()

The Run function is indended to contain the actual user Analysis, while the FillHistograms function should fill user histograms (for example on selected particles or jets). Input for the analysis comes from the different containers attached to the task, connecting to data from the input event. Users must not overwrite the function UserExec as it contains further functionality essential for the AliAnalysisTaskEmcal to work.

In case the AliAnalysisTaskEmcal should handle the output as well, which is the normal behaviour, the task should be configured to also fill histograms. In this case several general histograms monitoring the event selection are filled as well, among them the vertex distribution before and after selection, but also Monte-Carlo related information like the cross section or the number of trials from the event generator. Furthermore the list fOutput can handle all the user histograms. For this the function UserCreateOutputObjects needs to be implemented by the user and the corresponding function of the base class has to be called at the beginning.

In the Add macro use the named constructor in order to setup the task and attach it to the analysis manager.

Using the EMCAL containers

EMCAL containers are used to handle arrays of objects (particles, clusters, jets) shared among different tasks within the input ESD or AOD event via an easy interface hiding the direct access from the user. Each task can handle several containers as needed. Once they are defined, the AliAnalysisTaskEmcal will automatically connect them to the content they are supposed to handle, so the content can be used from that moment on. Normally EMCAL containers are defined in the add macro of the task.

  • In the add task users tasks need to create a container which can connect to the array inside the input event. It is important that the name provided matches the name of the content in the input event.
      AliParticleContainer *cont = task->AddParticleContainer("tracks");
      cont->SetName("MyTrackContainer");
      
    If one likes, one can apply also kinematical cuts
      ...
      cont->SetMinPt(0.5);
      cont->SetEtaRange(-0.8, 0.8);
      ...
      
  • In the user task one needs to get the container from the task. Afterwards one can iterate over the content
      ...
      AliParticleContainer *trackcont = GetParticleContainer("MyTrackContainer");
      trackcont->ResetCurrentID(-1);
      AliVParticle *track;
      while((track = trackcont->GetNextAcceptParticle())){
    Do something with the particle
      }
      
    The loop is done only on particles surviving the kinematical selection.

Using the virtual track selection

Track selection is normally applied in the track selection task as part of the framework. In case a more strict track selection needs to be applied, users should use the virtual track selection. The virtual track selection provides an interface handling the track selection in a seemless way both for ESDs and AODs. The selection criteria have to be implemented by the user.

AliEmcalTrackSelectionESD *sel = new AliEmcalTrackSelectionESD;
sel->AddTrackCuts(AliESDtrackCuts::GetStandardITSTPCTrackCuts2011(kTRUE, 1));

Inside the task the virtual track selection can be used in two ways: Either one checks for every track separate, via the function IsTrackAccepted, or one requests a TObjArray of all accepted tracks via GetAcceptedTracks. Everything needed at this step is provided by AliEmcalTrackSelection, the virtual base class.