CDF_2009_S8233977.cc

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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/RivetAIDA.hh"
#include "Rivet/Tools/Logging.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {


  /* @brief CDF Run II min-bias cross-section
   * @author Hendrik Hoeth
   *
   * Measurement of \f$ \langle p_T \rangle \f$ vs. \f$ n_\text{ch} \f$,
   * the track \f$ p_T \f$ distribution, and the \f$ \sum E_T \f$ distribution.
   * Particles are selected within |eta|<1 and with pT>0.4 GeV.
   * There is no pT cut for the \f$ \sum E_T \f$ measurement.
   *
   * @par Run conditions
   *
   * @arg \f$ \sqrt{s} = \f$ 1960 GeV
   * @arg Run with generic QCD events.
   * @arg Set particles with c*tau > 10 mm stable
   *
   */
  class CDF_2009_S8233977 : public Analysis {
  public:

    /// Constructor
    CDF_2009_S8233977()
      : Analysis("CDF_2009_S8233977"),
        _sumWeightSelected(0.0)
    {
      setBeams(PROTON, ANTIPROTON);
      setNeedsCrossSection(true);
    }
 
 
    /// @name Analysis methods
    //@{

    /// Book histograms and projections
    void init() {
      addProjection(ChargedFinalState(-4.7, 4.7, 0.0*GeV), "TriggerFS");
      addProjection(FinalState(-1.0, 1.0, 0.0*GeV), "EtFS");
      addProjection(ChargedFinalState(-1.0, 1.0, 0.4*GeV), "CFS");

      _hist_pt = bookHistogram1D(1, 1, 1);
      _hist_pt_vs_multiplicity = bookProfile1D(2, 1, 1);
      _hist_sumEt = bookHistogram1D(3, 1, 1);
    }


 
    /// Do the analysis
    void analyze(const Event& evt) {
      // Trigger: need at least one charged particle in both -4.7 < eta < -3.7 and 3.7 < eta < 4.7
      const FinalState& trigfs = applyProjection<FinalState>(evt, "TriggerFS");
      unsigned int n_plus(0), n_minus(0);
      foreach (const Particle& p, trigfs.particles()) {
        const double eta = p.momentum().eta();
        if (inRange(eta, -4.7, -3.7)) n_minus++;
        else if (inRange(eta, 3.7, 4.7)) n_plus++;
      }
      getLog() << Log::DEBUG << "Trigger -: " << n_minus << ", Trigger +: " << n_plus << endl;
      if (n_plus == 0 || n_minus == 0) vetoEvent;

      // Get the event weight
      const double weight = evt.weight();

      /// @todo The pT and sum(ET) distributions look slightly different from
      ///       Niccolo's Monte Carlo plots. Still waiting for his answer.

      const ChargedFinalState& trackfs = applyProjection<ChargedFinalState>(evt, "CFS");
      const size_t numParticles = trackfs.size();
      foreach (const Particle& p, trackfs.particles()) {
        const double pT = p.momentum().pT() / GeV;
        _hist_pt_vs_multiplicity->fill(numParticles, pT, weight);
     
        // The weight for entries in the pT distribution should be weight/(pT*dPhi*dy).
        //
        // - dPhi = 2*PI
        //
        // - dy depends on the pT: They calculate y assuming the particle has the
        //   pion mass and assuming that eta=1:
        //   dy = 2 * 1/2 * ln [(sqrt(m^2 + (a+1)*pT^2) + a*pT) / (sqrt(m^2 + (a+1)*pT^2) - a*pT)]
        //   with a = sinh(1).
        //
        // sinh(1) = 1.1752012
        // m(charged pion)^2 = (139.57 MeV)^2 = 0.019479785 GeV^2
        const double sinh1 = 1.1752012;
        const double apT  = sinh1 * pT;
        const double mPi = 139.57*MeV;
        const double root = sqrt(mPi*mPi + (1+sinh1)*pT*pT);
        const double dy = std::log((root+apT)/(root-apT));
        const double dphi = TWOPI;
        _hist_pt->fill(pT, weight/(pT*dphi*dy));
      }

      // Calc sum(Et) from calo particles
      const FinalState& etfs = applyProjection<FinalState>(evt, "EtFS");
      double sumEt = 0.0;
      foreach (const Particle& p, etfs.particles()) {
        sumEt += p.momentum().Et();
      }
      _hist_sumEt->fill(sumEt, weight);
      _sumWeightSelected += evt.weight();
    }

 
 
    /// Normalize histos
    void finalize() {
      scale(_hist_sumEt, crossSection()/millibarn/(4*M_PI*_sumWeightSelected));
      scale(_hist_pt, crossSection()/millibarn/_sumWeightSelected);
      getLog() << Log::DEBUG << "sumOfWeights()     = " << sumOfWeights() << std::endl;
      getLog() << Log::DEBUG << "_sumWeightSelected = " << _sumWeightSelected << std::endl;
    }
 
    //@}


  private:

    double _sumWeightSelected;
    AIDA::IProfile1D *_hist_pt_vs_multiplicity;
    AIDA::IHistogram1D *_hist_pt;
    AIDA::IHistogram1D *_hist_sumEt;

  };


  // This global object acts as a hook for the plugin system
  AnalysisBuilder<CDF_2009_S8233977> plugin_CDF_2009_S8233977;

}