Rivet analyses

title: BESII_2007_I728304

$\psi(2S)\to\pi^+\pi^- J/\psi$

Experiment: BESII (BEPC)

Inspire ID: 728304

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 645 (2007) 19-25

Beams: e- e+

Beam energies: (1.8, 1.8)GeV

Run details: - e+e- > psi(2S)

Measurement of the $\pi^+\pi^-$ mass and angular distributions in $\psi(2S)\to\pi^+\pi^- J/\psi$. The data was extract from the figures in the paper which are corrected for effciency/acceptance.

Source code:BESII_2007_I728304.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief psi(2S) -> J/psi pi+ pi- class BESII_2007_I728304 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2007_I728304);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 100443);
  declare(ufs, "UFS");
  DecayedParticles psi(ufs);
  psi.addStable(PID::PI0);
  psi.addStable(PID::JPSI);
  declare(psi, "psi");
  // histos
  for (unsigned int ix = 0; ix < 3; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles psi = apply<DecayedParticles>(event, "psi");
  // loop over particles
  for (unsigned int ix = 0; ix < psi.decaying().size(); ++ix) {
    if (!psi.modeMatches(ix, 3, mode)) continue;
    const Particle& pip = psi.decayProducts()[ix].at(211)[0];
    const Particle& pim = psi.decayProducts()[ix].at(-211)[0];
    FourMomentum pSigma = pip.momentum() + pim.momentum();
    _h[0]->fill(pSigma.mass() / GeV);
    const double cSigma = pSigma.z() / pSigma.p3().mod();
    _h[1]->fill(cSigma);
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(pSigma.betaVec());
    FourMomentum ppip = boost.transform(pip.momentum());
    const double cPi = pSigma.p3().unit().dot(ppip.p3().unit());
    _h[2]->fill(cPi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1.0, false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[3];
const map<PdgId, unsigned int> mode = {{211, 1}, {-211, 1}, {443, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BESII_2007_I728304);

} ```