Rivet analyses

title: EHS_1988_I265504

Charged-particle production in $K^+ p$, $\pi^+ p$ 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 $p$, $\pi^+$ and $K^+$ with $250\,\GeV/c$. Measured spectra are for positively charged hadrons $C^+$ and negative charge pions $\pi^-$. $C^+$ excludes slow protons with $p < 1.2\,\GeV/c$ 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

```c++ // -- 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);

} ```