Rivet analyses

Charged-particle production in K+p, π+p and pp interactions at $250 \GeV/c$

Experiment: EHS (SPS)

Inspire ID: 265504

Status: VALIDATED

Authors: - Felix Riehn

References: - Z.Phys.C39 (1988), 311

Beams: p+ p+, 211 p+, 321 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, π+ and K+ with $250\,\GeV/c$. Measured spectra are for positively charged hadrons C+ and negative charge pions π−. C+ excludes slow protons with $p < 1.2\,\GeV/c$ in the laboratory. Final spectra are in center-of-mass variables: xF, y and pT.

Source code:EHS_1988_I265504.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Event.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {


  class EHS_1988_I265504 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_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:
          book(_h_cpos_xF, 1, 1, 1);
          book(_h_cpos_eta, 3, 1, 1);
          book(_h_cpos_pT2, 5, 1, 1);
          book(_h_cneg_xF, 2, 1, 1);
          book(_h_cneg_eta, 4, 1, 1);
          book(_h_cneg_pT2, 6, 1, 1);
          break;

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

        case PID::PROTON:
          book(_h_cpos_xF, 1, 1, 3);
          book(_h_cpos_eta, 3, 1, 3);
          book(_h_cpos_pT2, 5, 1, 3);
          book(_h_cneg_xF, 2, 1, 3);
          book(_h_cneg_eta, 4, 1, 3);
          book(_h_cneg_pT2, 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 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);
          _h_cpos_pT2->fill(p.pT2());
          _h_cpos_eta->fill(pcm.eta());
        }
        else if (p.pid() == PID::PIMINUS) {
          _h_cneg_xF->fill(xF);
          _h_cneg_pT2->fill(p.pT2());
          _h_cneg_eta->fill(pcm.eta());
        }
      }
    }


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

    /// @}


    /// @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;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(EHS_1988_I265504);

}