Rivet analyses

title: STAR_2009_UE_HELEN

UE measurement in $pp$ at 200 GeV

Experiment: STAR (RHIC)

Spires ID: None

Status: PRELIMINARY

Authors: - Helen Caines - Hendrik Hoeth

References: - arXiv: 0910.5203 - arXiv: 0907.3460

Beams: p+ p+

Beam energies: (100.0, 100.0)GeV

Run details: - $pp$ at 200 GeV

WARNING! Mark as "STAR preliminary" and contact authors when using this! UE analysis similar to Rick Field's leading jet analysis. SIScone with radius/resolution parameter R=0.7 is used. Particles with $pT > 0.2~\text{GeV}$ and $|\eta| < 1$ are included in the analysis. All particles are assumed to have zero mass. Only jets with neutral energy $< 0.7$ are included. For the transMIN and transMAX $\Delta(\phi)$ is between $\pi/3$ and $2\pi/3$, and $\Delta(\eta) < 2.0$. For the jet region the area of the jet is used for the normalization, i.e. the scaling factor is $\pi R^2$ and not $\mathrm{d}\phi\mathrm{d}\eta$ (this is different from what Rick Field does!). The tracking efficiency is $\sim 0.8$, but that is an approximation, as below $pT \sim 0.6~\text{GeV}$ it is falling quite steeply.

Source code:STAR_2009_UE_HELEN.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/MergedFinalState.hh"

include "Rivet/Projections/NeutralFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

include "Rivet/Tools/Random.hh"

include "fastjet/SISConePlugin.hh"

namespace Rivet {

/// @brief STAR underlying event /// /// @author Hendrik Hoeth class STAR_2009_UE_HELEN : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(STAR_2009_UE_HELEN);


/// @name Analysis methods
/// @{

void init() {
  // Charged final state, |eta|<1, pT>0.2GeV
  const Cut c = Cuts::abseta < 1.0 && Cuts::pT >= 0.2 * GeV;

  const ChargedFinalState cfs(c);
  declare(cfs, "CFS");

  // Neutral final state, |eta|<1, ET>0.2GeV (needed for the jets)
  const NeutralFinalState nfs(c);
  declare(nfs, "NFS");

  // STAR can't see neutrons and K^0_L
  VetoedFinalState vfs(nfs);
  vfs.vetoNeutrinos();
  vfs.addVetoPairId(PID::K0L);
  vfs.addVetoPairId(PID::NEUTRON);
  declare(vfs, "VFS");

  // Jets are reconstructed from charged and neutral particles,
  // and the cuts are different (pT vs. ET), so we need to merge them.
  const MergedFinalState jfs(cfs, vfs);
  declare(jfs, "JFS");

  // SISCone, R = 0.7, overlap_threshold = 0.75
  declare(FastJets(jfs, JetAlg::SISCONE, 0.7), "AllJets");

  // Book histograms
  book(_hist_pmaxnchg, 1, 1, 1);
  book(_hist_pminnchg, 2, 1, 1);
  book(_hist_anchg, 3, 1, 1);
}


// Do the analysis
void analyze(const Event& e) {
  const FinalState& cfs = apply<ChargedFinalState>(e, "CFS");
  if (cfs.particles().size() < 1) {
    MSG_DEBUG("Failed multiplicity cut");
    vetoEvent;
  }

  const Jets& alljets = apply<FastJets>(e, "AllJets").jetsByPt();
  MSG_DEBUG("Total jet multiplicity = " << alljets.size());

  // The jet acceptance region is |eta|<(1-R)=0.3  (with R = jet radius)
  // Jets also must have a neutral energy fraction of < 0.7
  Jets jets;
  for (const Jet& jet : alljets) {
    if (jet.neutralEnergy() / jet.totalEnergy() < 0.7 && jet.abseta() < 0.3) {
      jets.push_back(jet);
    }
  }

  // This analysis requires a di-jet like event.
  // WARNING: There is more data in preparation, some of which
  //          does _not_ have this constraint!
  if (jets.size() != 2) {
    MSG_DEBUG("Failed jet multiplicity cut");
    vetoEvent;
  }

  // The di-jet constraints in this analysis are:
  // - 2 and only 2 jets in the acceptance region
  // - delta(Phi) between the jets is > 150 degrees
  // - Pt_awayjet/Pt_towards_jet > 0.7
  if (deltaPhi(jets[0].phi(), jets[1].phi()) <= 5 * PI / 6 || jets[1].pT() / jets[0].pT() <= 0.7) {
    MSG_DEBUG("Failed di-jet criteria");
    vetoEvent;
  }

  // Now lets start ...
  const double jetphi = jets[0].phi();
  const double jetpT = jets[0].pT() / GeV;

  size_t numTrans1(0), numTrans2(0), numAway(0);

  // Calculate all the charged stuff
  for (const Particle& p : cfs.particles()) {
    const double dPhi = deltaPhi(p.phi(), jetphi);
    const double pT = p.pT();
    const double phi = p.phi();
    double rotatedphi = phi - jetphi;
    while (rotatedphi < 0) rotatedphi += 2 * PI;

    // @TODO: WARNING: The following lines are a hack to correct
    //        for the STAR tracking efficiency. Once we have the
    //        final numbers (corrected to hadron level), we need
    //        to remove this!!!!
    if (1.0 * rand01() > 0.87834 - exp(-1.48994 - 0.788432 * pT)) {
      continue;
    }
    // -------- end of efficiency hack -------

    if (dPhi < PI / 3.0) {
      // toward
    }
    else if (dPhi < 2 * PI / 3.0) {
      if (rotatedphi <= PI) {
        ++numTrans1;
      }
      else {
        ++numTrans2;
      }
    }
    else {
      ++numAway;
    }
  } // end charged particle loop

  // Fill the histograms
  _hist_pmaxnchg->fill(jetpT, double(numTrans1 > numTrans2 ? numTrans1 : numTrans2) / (2 * PI / 3));
  _hist_pminnchg->fill(jetpT, double(numTrans1 < numTrans2 ? numTrans1 : numTrans2) / (2 * PI / 3));
  _hist_anchg->fill(jetpT, (double)numAway / (PI * 0.7 * 0.7)); // jet area = pi*R^2
}


void finalize() {
  /// @todo Really nothing to do?
}

/// @}

private:

Profile1DPtr _hist_pmaxnchg;
Profile1DPtr _hist_pminnchg;
Profile1DPtr _hist_anchg;

};

RIVET_DECLARE_PLUGIN(STAR_2009_UE_HELEN);

} ```