Rivet analyses

title: BABAR_2007_I729388

Cross section for $e^+e^-\to \psi(2S)\pi^+\pi^-$ at energies between 4 and 8 GeV

Experiment: BABAR (PEP-II)

Inspire ID: 729388

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 98 (2007) 212001

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to \psi(2S)\pi^+\pi^-$ at energies between 4 and 8 GeV using radiative return by BABAR.

Source code:BABAR_2007_I729388.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Add a short analysis description here class BABAR_2007_I729388 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2007_I729388);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  book(_nPsi2s, "TMP/psi2s");
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      --nRes[child.pid()];
      --ncount;
    }
    else
      findChildren(child, nRes, ncount);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  const FinalState& fs = apply<FinalState>(event, "FS");
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    // find the psi(2S)
    if (p.pid() == 100443) {
      map<long, int> nRes = nCount;
      int ncount = ntotal;
      findChildren(p, nRes, ncount);
      // omega pi+pi-
      if (ncount != 2) continue;
      bool matched = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 211) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _nPsi2s->fill();
        break;
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double sigma = _nPsi2s->val();
  double error = _nPsi2s->err();
  sigma *= crossSection() / sumOfWeights() / picobarn;
  error *= crossSection() / sumOfWeights() / picobarn;
  Estimate1DPtr mult;
  book(mult, 1, 1, 1);
  for (auto& b : mult->bins()) {
    if (inRange(sqrtS() / GeV, b.xMin(), b.xMax())) {
      b.set(sigma, error);
    }
  }
}

/// @}


/// @name Histograms
/// @{
CounterPtr _nPsi2s;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2007_I729388);

} ```