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BRAHMS_2004_I647076

Charged meson pT spectra for various rapidities in central Au--Au collisions at 200 GeV.
Experiment: BRAHMS (RHIC)
Inspire ID: 647076
Status: UNVALIDATED
Authors:
  • Christian Bierlich
References:
  • Phys.Rev.Lett. 94 (2005) 162301
  • 10.1103/PhysRevLett.94.162301
  • arXiv: nucl-ex/043050
Beams: 1000791970 1000791970
Beam energies: (19700.0, 19700.0) GeV
Run details:
  • Au Au minimum bias events, only 5% most central events used in analysis.

Measurements of invariant $p_\perp$ spectra for pions and kaons in the 5% most central Au--Au collisions at $\sqrt{s_{NN}} = 200$ GeV, over a broad rapidity range $-0.1 < y < 3.5$. The paper quotes several derived quantities, like total $dN/dy$ and $\langle p_\perp \rangle$, which can be fitted from the spectra produced in this analysis.

Source code: BRAHMS_2004_I647076.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/SingleValueProjection.hh"
#include "Rivet/Projections/ImpactParameterProjection.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Tools/RHICCommon.hh"

namespace Rivet {


  /// @brief Brahms pT spectra for id particles (pi+, pi-, K+, K-)
  //  in small bins of rapidity, 5% central collisions. 
  //  System: AuAu @ 200GeV/nn.
  class BRAHMS_2004_I647076 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(BRAHMS_2004_I647076);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      // Centrality Projection.
      declareCentrality(BRAHMSCentrality(), "BRAHMS_2004_AUAUCentrality","mult","BCEN");
      // TODO: Feed down correction is unclear.
      declare(FinalState(Cuts::rap < 4 && Cuts::rap > -0.1 && Cuts::pT > 100*MeV), "FS");
      // The measured rapidity intervals for pions.
      rapIntervalsPi = {{-0.1,0.},{0.,0.1},{0.4,0.6},{0.6,0.8},{0.8,1.0},
        {1.0,1.2},{1.2,1.4},{2.1,2.3},{2.4,2.6},{3.0,3.1},{3.1,3.2},{3.2,3.3},
        {3.3,3.4},{3.4,3.66}};
      // The measured rapidity intervals for kaons.
      rapIntervalsK = {{-0.1,0.},{0.,0.1},{0.4,0.6},{0.6,0.8},{0.8,1.0},
        {1.0,1.2},{2.0,2.2},{2.3,2.5},{2.9,3.0},{3.0,3.1},{3.1,3.2},{3.2,3.4}};
      // Book histograms
      piPlus.resize(rapIntervalsPi.size());
      piMinus.resize(rapIntervalsPi.size());
      for (int i = 1, N = rapIntervalsPi.size(); i <= N; ++i) {
        book(piPlus[i], 1, 1, i);
        book(piMinus[i], 1, 1, 14 + i);
      }

      kPlus.resize(rapIntervalsK.size());
      kMinus.resize(rapIntervalsK.size());
      for (int i = 1, N = rapIntervalsK.size(); i <= N; ++i) {
        book(kPlus[i], 2, 1, i);
        book(kMinus[i], 2, 1, 12 + i);
      }
      // Counter for accepted sum of weights (centrality cut).
      book(centSow, "centSow");

    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Reject all non-central events. The paper does not speak of 
      // any other event trigger, which in any case should matter
      // little for central events.
      if(apply<CentralityProjection>(event,"BCEN")() > 5.0) return;
      // Keep track of sum of weights.
      centSow->fill();
      const FinalState& fs = apply<FinalState>(event,"FS");
      // Loop over particles.
      for (const auto& p : fs.particles()) {
        const double y = p.rapidity();
	const double pT = p.pT();
	const int id = p.pid();
	// First pions.
	if (abs(id) == 211) {
          // Protect against decaying K0S and Lambda
	  if (p.hasAncestor(310) || p.hasAncestor(-310) || 
	    p.hasAncestor(3122) || p.hasAncestor(3122)) continue;
	  for (int i = 0, N = rapIntervalsPi.size(); i < N; ++i) {
	    if (y > rapIntervalsPi[i].first && y <= rapIntervalsPi[i].second) {
	      const double dy = rapIntervalsPi[i].second - rapIntervalsPi[i].first;
	      const double nWeight = 1.0 / ( 2.*M_PI*pT*dy);
	      if (id == 211) piPlus[i]->fill(pT, nWeight);
	      else piMinus[i]->fill(pT, nWeight);
	      break;
	    }
	  } 
	}
	// Then kaons.
	else if (abs(id) == 321) {
	  for (int i = 0, N = rapIntervalsK.size(); i < N; ++i) {
	    if (y > rapIntervalsK[i].first && y <= rapIntervalsK[i].second) {
	      const double dy = rapIntervalsK[i].second - rapIntervalsK[i].first;
	      const double nWeight = 1.0 / ( 2.*M_PI*pT*dy);
	      if (id == 321) kPlus[i]->fill(pT, nWeight);
	      else kMinus[i]->fill(pT, nWeight);
	      break;
	    }
	  } 
	}
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // Normalize all histograms to per-event yields.
      for (int i = 0, N = rapIntervalsPi.size(); i < N; ++i) {
        piPlus[i]->scaleW(1./centSow->sumW());
        piMinus[i]->scaleW(1./centSow->sumW());
      }
      for (int i = 0, N = rapIntervalsK.size(); i < N; ++i) {
        kPlus[i]->scaleW(1./centSow->sumW());
        kMinus[i]->scaleW(1./centSow->sumW());
      }

    }

    //@}

    // The rapidity intervals.
    vector<pair<double, double> > rapIntervalsPi;
    vector<pair<double, double> > rapIntervalsK;

    /// @name Histograms
    //@{
    vector<Histo1DPtr> piPlus;
    vector<Histo1DPtr> piMinus;
    vector<Histo1DPtr> kPlus;
    vector<Histo1DPtr> kMinus;
    CounterPtr centSow;
    //@}
  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(BRAHMS_2004_I647076);
}