Rivet analyses

title: ALICE_2021_I1898832

J/$\psi$ production for midrapidity at $\sqrt{s}=13$ TeV

Experiment: ALICE (LHC)

Inspire ID: 1898832

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2108.01906

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - J/;Psi production at 13 TeV

Measurement of J/$\psi$ production for central rapidities ($|y|<0.9$$) by the ALICE collaboration at 13 TeV.

Source code:ALICE_2021_I1898832.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi production at 13 TeV (central rapidity) class ALICE_2021_I1898832 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ALICE_2021_I1898832);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(Cuts::pid == 443), "UFS");
  book(_h_pT, 1, 1, 1);
  book(_h_y1, 2, 1, 1);
  book(_h_y2, 3, 1, 1);
  _axis = YODA::Axis<double>({0., 0.5, 1., 2., 3., 4., 5., 7., 10., 15., 20., 25., 30., 40.});
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _h_pT->xEdges();
  // loop over J/Psi
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    const double absrap = p.absrap();
    if (absrap > 0.9) continue;

    _h_pT->fill(disc(p.perp()));

    _h_y1->fill("0.0"s);

    string yedge("0.7");
    if (absrap < 0.2)
      yedge = "0.1";
    else if (absrap < 0.5)
      yedge = "0.3";

    _h_y2->fill(yedge);
  }
}

string disc(const double value) const {
  string edge("OTHER");
  const size_t idx = _axis.index(value);
  if (0 < idx && idx <= _axis.numBins()) return _edges[idx - 1];
  return edge;
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / microbarn / sumOfWeights();
  // 1.8 for the rapidity -0.9 to 0.9 in the double differential
  scale(_h_pT, fact / 1.8);
  for (auto& b : _h_pT->bins()) {
    b.scaleW(1. / _axis.width(b.index()));
  }
  // divide by range -0.9 to 0.9 as quoted as dsigma/dy
  scale(_h_y1, fact / 1.8);
  // 0.5 as fold + and - rapidity
  scale(_h_y2, 0.5 * fact);
  for (auto& b : _h_y2->bins()) {
    if (b.index() == 1)
      b.scaleW(1. / 0.2);
    else if (b.index() == 2)
      b.scaleW(1. / 0.3);
    else
      b.scaleW(1. / 0.4);
  }
}

///@}


/// @name Histograms
///@{
BinnedHistoPtr<string> _h_pT, _h_y1, _h_y2;
vector<string> _edges;
YODA::Axis<double> _axis;
///@}

};

RIVET_DECLARE_PLUGIN(ALICE_2021_I1898832);

} ```