EMCAL FastJet Analysis

Introduction

Using the FastJet package for jet finding using ALICE EMCAL data. Purpose is to run the package in the HLT for selecting jets meeting certain criteria.

Steps to be followed:

• Create MC jets
• Do the reconstruction
• Run FastJet (mainly with anti-kt algorithm)
• Optimize the performance
• Implement and commission the HLT jet trigger component

Create MC jets

Using all detectors in the simulation and one ptHardBin producing 10,000 events:

    case kPythia6Jets104_125:
    {
        comment = comment.Append(":Pythia jets 105-125 GeV @ 7.00 TeV");
        AliGenPythia * gener = new AliGenPythia(-1);
        gener->SetEnergyCMS(7000.);//        Centre of mass energy
        gener->SetProcess(kPyJets);//        Process type
        gener->SetJetEtaRange(-0.5, 0.5);//  Final state kinematic cuts
        gener->SetJetPhiRange(0., 360.);
        gener->SetJetEtRange(10., 1000.);
        gener->SetGluonRadiation(1,1);
        //   Structure function
        gener->SetStrucFunc(kCTEQ4L);
        gener->SetPtHard(104., 125.);// Pt transfer of the hard scattering
        gener->SetPycellParameters(2., 274, 432, 0., 4., 5., 1.0);
        gener->SetForceDecay(kAll);//  Decay type (semielectronic, etc.)
        gener->SetProjectile("p", 1, 1) ;
        gener->SetTarget("p", 1, 1) ;
        gGener=gener;
      }

Run the reconstruction

Full reconstruction:

void rec() {
  AliReconstruction reco;

  reco.SetWriteESDfriend(kTRUE);
  reco.SetFractionFriends(1.0);
  reco.SetWriteAlignmentData();

  reco.SetDefaultStorage("local://$ALICE_ROOT/OCDB");
  reco.SetSpecificStorage("GRP/GRP/Data",
                          Form("local://%s",gSystem->pwd()));
  reco.SetRunPlaneEff(kTRUE);

  TStopwatch timer;
  timer.Start();
  reco.Run();
  timer.Stop();
  timer.Print();
}

Run FastJet

• TPC tracks + "tracks" from EMCal
• |η| < 0.5 in jets
• 1.08 < φ < 2.7 (107 degrees acceptance of EMCal subtracting a "keepOut" zone of R=0.4) in jets
• AntiKt algorithm, with R=0.4 and maximum rapidity up to which ghosts are generated 0.9
• Following plots without background subtraction

"particle": what's coming out of MC, "detector": what's coming out of the reconstruction

1,000 events, without φ cut, without EMCal clusters

pT of tracks at detector level	pT of tracks at particle level

pT distribution of jets at detector level	pT distribution of jets at particle level

Eta distribution of jets at detector level	Phi distribution of jets at detector level

(Eta_particle - Eta_detector) distribution of jets	(Phi_particle - Phi_detector) distribution of jets

(pT_particle - pT_detector) distribution of jets

10,000 events, with φ cut, with EMCal clusters

pT distribution of jets at detector level	pT distribution of jets at particle level

Eta distribution of jets at detector level	pT distribution of particle (red) and detector (black) jets

(Eta_particle - Eta_detector) distribution of jets	(Phi_particle - Phi_detector) distribution of jets

(pT_particle - pT_detector) distribution of jets

10,000 events, with φ and additional cuts, with EMCal clusters

• Additional cuts: tracks pT > 0.7 GeV and jets' pT > 50 GeV

pT distribution of jets at detector level	pT distribution of jets at particle level

pT distribution of jets at particle level (red) and at detector level (black)

Eta distribution of jets at detector level	Eta-Phi distribution of EMCal clusters

(Eta_particle - Eta_detector) distribution of jets	(Phi_particle - Phi_detector) distribution of jets

(pT_particle - pT_detector) distribution of jets

Neutral Energy Fraction distribution of jets Sum(Neutral particle pT)/(Jet pT)	Fragmentation Function of jets (Particle pT)/(Jet pT)

10,000 events, with φ and additional cuts, with EMCal clusters, removed energy double counting

• Additional cuts: tracks pT > 0.7 GeV and jets' pT > 50 GeV
• Removed double counting of energy from charged tracks. Sum the P of all tracks matched per cluster and subtract that from the energy of the cluster; that corrected energy is used in FastJet

pT distribution of jets at detector level	pT distribution of jets at particle level

pT distribution of jets at particle level (red) and at detector level (black)

(Eta_particle - Eta_detector) distribution of jets	(Phi_particle - Phi_detector) distribution of jets

(pT_particle - pT_detector) distribution of jets	Correlation (pT_particle - pT_detector)/(pT_particle + pT_detector)

Neutral Energy Fraction distribution of jets Sum(Neutral particle pT)/(Jet pT)	Correlation Y projection

Implementation and commission of the HLT jet trigger component

Useful links

• EMCal Weekly meeting 21 July 2011 - "A FastJet Plugin for HLT and Offline"
• HLT Physics Workshop 28 July 2011 - "EMCal Jet Trigger"

Major Updates: LeonidasXaplanteris - 04 August 2011

Responsible: LeonidasXaplanteris