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EHS_1988_I265504

Charged-particle production in $K^+ p$, $\pi^+ p$ and $pp$ interactions at $250 \text{GeV}/c$
Experiment: EHS (SPS)
Inspire ID: 265504
Status: VALIDATED
Authors:
  • Felix Riehn
References:
  • Z.Phys.C39 (1988), 311
Beams: p+ p+, 0 p+, 0 p+
Beam energies: (250.0, 0.0); (250.0, 0.0); (250.0, 0.0) GeV
Run details:
  • Inelastic interactions in CM frame, excluding slow protons in the lab. frame with p < 1.2 GeV/$c$

Measurement of charged particle production spectra in longitudinal and transverse momentum as well as rapidity by the EHS/NA22 collaboration at the SPS. Experiment was done with a fixed hydrogen target and beams of $p$, $\pi^+$ and $K^+$ with $250\,\text{GeV}/c$. Measured spectra are for positively charged hadrons $C^+$ and negative charge pions $\pi^-$. $C^+$ excludes slow protons with $p < 1.2\,\text{GeV}/c$ in the laboratory. Final spectra are in center-of-mass variables: $x_\mathrm{F}$, $y$ and $p_\mathrm{T}$.

Source code: EHS_1988_I265504.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Event.hh"

namespace Rivet {


  class EHS_1988_I265504 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(EHS_1988_I265504);


    /// @name Analysis methods
    //@{

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

      declare(ChargedFinalState(), "CFS");
      declare(Beam(),"Beam");

      switch ( beamIds().first ) {
      case PID::PIPLUS:
        _h_cpos_xF = bookHisto1D(1, 1, 1);
        _h_cpos_eta = bookHisto1D(3, 1, 1);
        _h_cpos_pT2 = bookHisto1D(5, 1, 1);
        _h_cneg_xF = bookHisto1D(2, 1, 1);
        _h_cneg_eta = bookHisto1D(4, 1, 1);
        _h_cneg_pT2 = bookHisto1D(6, 1, 1);
        break;

      case PID::KPLUS:
        _h_cpos_xF = bookHisto1D(1, 1, 2);
        _h_cpos_eta = bookHisto1D(3, 1, 2);
        _h_cpos_pT2 = bookHisto1D(5, 1, 2);
        _h_cneg_xF = bookHisto1D(2, 1, 2);
        _h_cneg_eta = bookHisto1D(4, 1, 2);
        _h_cneg_pT2 = bookHisto1D(6, 1, 2);
        break;

      case PID::PROTON:
        _h_cpos_xF = bookHisto1D(1, 1, 3);
        _h_cpos_eta = bookHisto1D(3, 1, 3);
        _h_cpos_pT2 = bookHisto1D(5, 1, 3);
        _h_cneg_xF = bookHisto1D(2, 1, 3);
        _h_cneg_eta = bookHisto1D(4, 1, 3);
        _h_cneg_pT2 = bookHisto1D(6, 1, 3);
        break;
      }

      // Calculate boost from lab to CM frame
      _beamboost = cmsTransform( beams() );
      MSG_DEBUG("Boost vector: " << _beamboost );

      // Transform beam into CMS frame
      Particle _beam_cm = beams().first;
      _beam_cm.transformBy(_beamboost);
      // Beam momentum in CM frame defines Feynman-x
      _pz_max = _beam_cm.pz();

    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const double weight = event.weight();

      const FinalState& fs = apply<FinalState>(event, "CFS");
      for (const Particle& p: fs.particles()) {
        // Only interested in pi- or positively charged
        if (p.charge() < 0 && p.pid() != PID::PIMINUS) continue;
        // Slow proton cut: reject lab momenta < 1.2GeV
        if (p.pid() == PID::PROTON && p.p() < 1.2*GeV) continue;
        // Transform to cm frame
        const FourMomentum pcm = _beamboost.transform(p);
        const double xF = pcm.pz()/_pz_max;

        if (p.charge() > 0) {
          _h_cpos_xF->fill( xF, weight);
          _h_cpos_pT2->fill( p.pT2(), weight);
          _h_cpos_eta->fill( p.eta(), weight);
        } else if (p.pid() == PID::PIMINUS) {
          _h_cneg_xF->fill( xF, weight);
          _h_cneg_pT2->fill( p.pT2(), weight);
          _h_cneg_eta->fill( p.eta(), weight);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale( {_h_cpos_xF, _h_cpos_pT2,_h_cpos_eta, _h_cneg_xF, _h_cneg_eta, _h_cneg_pT2},
             crossSection()/millibarn/sumOfWeights() );
    }

    //@}


    /// @name Histograms
    //@{
    LorentzTransform _beamboost;
    double _pz_max;
    Histo1DPtr _h_cpos_xF, _h_cpos_eta, _h_cpos_pT2;
    Histo1DPtr _h_cneg_xF, _h_cneg_eta, _h_cneg_pT2;
    //@}

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(EHS_1988_I265504);

}