Rivet analyses

title: NA22_1986_I18431

Multiplicity distributions in $pp$, $K^+ p$ and $\pi^+ p$ at $p_{\mathrm{lab}} = 250$ GeV/c

Experiment: NA22 (SPS)

Inspire ID: 18431

Status: VALIDATED

Authors: - Christian Bierlich

References: - Z.Phys. C32 (1986) 475

Beams: p+ p+, 321 p+, 211 p+

Beam energies: (250.0, 0.0); (250.0, 0.0); (250.0, 0.0)GeV

Run details: - Fixed target events with $p$, $K^+$ and $\pi^+$ hitting a proton target.

Charged multiplicity distributions of $pp$, $K^+ p$ and $\pi^+ p$ fixed target collisions, $p_{\mathrm{lab}} = 250$ GeV/c or equivalently $\sqrt{s} = 21.7$ GeV/c (pp).

Source code:NA22_1986_I18431.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {

/// NA22 min bias multiplicity distributions. class NA22_1986_I18431 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(NA22_1986_I18431);


/// @name Analysis methods
/// @{

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

  declare(ChargedFinalState(), "CFS");

  // Figure out beam type
  const ParticlePair& beam = beams();
  int btype = 0;
  if (beam.first.pid() == PID::PIPLUS && beam.second.pid() == PID::PROTON) {
    btype = 1;
    sf *= 20.94; // simga_inel(pi+ p) from DOI:10.1007/BF01550769
  }
  else if (beam.first.pid() == PID::KPLUS && beam.second.pid() == PID::PROTON) {
    btype = 2;
    sf *= 17.72; // simga_inel(K+ p) from DOI:10.1007/BF01550769
  }
  else if (beam.first.pid() == PID::PROTON && beam.second.pid() == PID::PROTON) {
    btype = 3;
    sf *= 32.40; // simga_inel(p p) from DOI:10.1007/BF01550769
  }
  else {
    MSG_ERROR("Beam error: Not compatible!");
    return;
  }

  // Book histo for appropriate beam type
  if (btype == 3)
    book(_h_mult2, btype, 1, 1);
  else
    book(_h_mult1, btype, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  size_t nfs = apply<ChargedFinalState>(event, "CFS").size();
  if (nfs >= 30) nfs = 30;
  if (_h_mult1) {
    string edge = to_string(nfs) + ".0";
    if (nfs == 30) edge = ">= 30.0";
    _h_mult1->fill(edge);
  }
  if (_h_mult2) _h_mult2->fill(nfs);
}


/// Normalise histograms etc., after the run
void finalize() {
  if (_h_mult1) normalize(_h_mult1, sf); // normalize to 2 to account for bin width
  if (_h_mult2) normalize(_h_mult2, sf); // normalize to 2 to account for bin width
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_mult1;
BinnedHistoPtr<int> _h_mult2;
double sf = 2.0;
/// @}

};

RIVET_DECLARE_PLUGIN(NA22_1986_I18431);

} ```