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ALICE_2016_I1507157

Angular correlations of identified particles at 7 TeV.
Experiment: ALICE (LHC)
Inspire ID: 1507157
Status: UNVALIDATED
Authors:
  • Christian Bierlich
References:
  • Eur.Phys.J.C77(2017)no.8,569
  • DOI:10.1140/epjc/s10052-017-5129-6
  • arXiv: 1612.08975
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Proton-proton minium bias events at 7 TeV.

Angular correlations between like-sign and opposite-sign identified particles, integrated over $\Delta \eta < 1.3$. The analysis makes use of event mixing to remove background. The current implementation of the event micing is not validated by experiment, and should be used with caution. Note in particular that for the event mixing to behave sensibly, event weights are assumed to be unity. Do not run this analysis with weighted events

Source code: ALICE_2016_I1507157.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/AliceCommon.hh"
#include "Rivet/Projections/PrimaryParticles.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/EventMixingFinalState.hh"
namespace Rivet {


  /// @brief Correlations of identified particles in pp.
  /// Also showcasing use of EventMixingFinalState.
  class ALICE_2016_I1507157 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ALICE_2016_I1507157);


    /// @name Analysis methods
    //@{

    /// @brief Calculate angular distance between particles.
    double phaseDif(double a1, double a2){
      double dif = a1 - a2;
      while (dif < -M_PI/2)
        dif += 2*M_PI;
      while (dif > 3*M_PI/2)
        dif -= 2*M_PI;
      return dif;
    }


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

      double etamax = 0.8;
      double pTmin = 0.5; // GeV

      // Trigger
      declare(ALICE::V0AndTrigger(), "V0-AND");
      // Charged tracks used to manage the mixing observable.
      ChargedFinalState cfsMult(Cuts::abseta < etamax);
      declare(cfsMult, "CFSMult");

      // Primary particles.
      PrimaryParticles pp({Rivet::PID::PIPLUS, Rivet::PID::KPLUS,
	Rivet::PID::K0S, Rivet::PID::K0L, Rivet::PID::PROTON,
	Rivet::PID::NEUTRON, Rivet::PID::LAMBDA, Rivet::PID::SIGMAMINUS,
       	Rivet::PID::SIGMAPLUS, Rivet::PID::XIMINUS, Rivet::PID::XI0,
	Rivet::PID::OMEGAMINUS},Cuts::abseta < etamax && Cuts::pT > pTmin*GeV);
      declare(pp,"APRIM");

      // The event mixing projection
      declare(EventMixingFinalState(cfsMult, pp, 5, 0, 100, 10),"EVM");
      // The particle pairs.
      pid = {{211, -211}, {321, -321}, {2212, -2212}, {3122, -3122}, {211, 211},
             {321, 321}, {2212, 2212}, {3122, 3122}, {2212, 3122}, {2212, -3122}};
      // The associated histograms in the data file.
      vector<string> refdata = {"d04-x01-y01","d04-x01-y02","d04-x01-y03",
        "d06-x01-y02","d05-x01-y01","d05-x01-y02","d05-x01-y03","d06-x01-y01",
        "d01-x01-y02","d02-x01-y02"};
      ratio.resize(refdata.size());
      signal.resize(refdata.size());
      background.resize(refdata.size());
      for (int i = 0, N = refdata.size(); i < N; ++i) {
        // The ratio plots.
        book(ratio[i], refdata[i], true);
      // Signal and mixed background.
        book(signal[i], "/TMP/" + refdata[i] + "-s");
        book(background[i], "/TMP/" + refdata[i] + "-b");
        // Number of signal and mixed pairs.
        nsp.push_back(0.);
        nmp.push_back(0.);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      // Triggering
      if (!apply<ALICE::V0AndTrigger>(event, "V0-AND")()) return;
      // The projections
      const PrimaryParticles& pp = 
        applyProjection<PrimaryParticles>(event,"APRIM");
      const EventMixingFinalState& evm = 
        applyProjection<EventMixingFinalState>(event, "EVM");

      // Test if we have enough mixing events available to continue.
      if (!evm.hasMixingEvents()) return;

      for(const Particle& p1 : pp.particles()) {
        // Start by doing the signal distributions
	for(const Particle& p2 : pp.particles()) {
	  if(isSame(p1,p2))
	    continue;
	  double dEta = abs(p1.eta() - p2.eta());
	  double dPhi = phaseDif(p1.phi(), p2.phi());
	  if(dEta < 1.3) {
	    for (int i = 0, N = pid.size(); i < N; ++i) {
	      int pid1 = pid[i].first;
	      int pid2 = pid[i].second;
	      bool samesign = (pid1 * pid2 > 0);
	      if (samesign && ((pid1 == p1.pid() && pid2 == p2.pid()) ||
		 (pid1 == -p1.pid() && pid2 == -p2.pid()))) {
	        signal[i]->fill(dPhi);
		nsp[i] += 1.0;
	      }
	      if (!samesign && abs(pid1) == abs(pid2) &&
		  pid1 == p1.pid() && pid2 == p2.pid()) {
	            signal[i]->fill(dPhi);
		    nsp[i] += 1.0;
	      }
	      if (!samesign && abs(pid1) != abs(pid2) &&
		  ( (pid1 == p1.pid() && pid2 == p2.pid()) ||
		  (pid2 == p1.pid() && pid1 == p2.pid()) ) ) {
	            signal[i]->fill(dPhi);
		    nsp[i] += 1.0;
	      }
	    }
	  }
	}
	// Then do the background distribution
	for(const Particle& pMix : evm.particles()){
	  double dEta = abs(p1.eta() - pMix.eta());
	  double dPhi = phaseDif(p1.phi(), pMix.phi());
	  if(dEta < 1.3) {
	    for (int i = 0, N = pid.size(); i < N; ++i) {
	      int pid1 = pid[i].first;
	      int pid2 = pid[i].second;
	      bool samesign = (pid1 * pid2 > 0);
	      if (samesign && ((pid1 == p1.pid() && pid2 == pMix.pid()) ||
		 (pid1 == -p1.pid() && pid2 == -pMix.pid()))) {
	            background[i]->fill(dPhi);
		    nmp[i] += 1.0;
	      }
	      if (!samesign && abs(pid1) == abs(pid2) &&
		  pid1 == p1.pid() && pid2 == pMix.pid()) {
	            background[i]->fill(dPhi);
		    nmp[i] += 1.0;
	      }
	      if (!samesign && abs(pid1) != abs(pid2) &&
		  ( (pid1 == p1.pid() && pid2 == pMix.pid()) ||
		  (pid2 == p1.pid() && pid1 == pMix.pid()) ) ) {
	            background[i]->fill(dPhi);
		    nmp[i] += 1.0;
	      }
	    }
	  }
	}
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (int i = 0, N = pid.size(); i < N; ++i) {
        double sc = nmp[i] / nsp[i];
        signal[i]->scaleW(sc);
        divide(signal[i],background[i],ratio[i]);
      }
    }

    //@}


    /// @name Histograms
    //@{
    vector<pair<int, int> > pid;
    vector<Histo1DPtr> signal;
    vector<Histo1DPtr> background;
    vector<Scatter2DPtr> ratio;
    vector<double> nsp;
    vector<double> nmp;

    //@}


  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ALICE_2016_I1507157);


}