Rivet analyses

title: BESII_2004_I650570

Mass and angular distributions in $J/\psi\to pK^-\bar\Lambda$ +c.c.

Experiment: BESII (BEPC)

Inspire ID: 650570

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 93 (2004) 112002

Beams: * *

Beam energies: ANY

Run details: - Any process producing j/psi, originally e+e-

Mass and angular distributions in $J/\psi\to pK^-\bar\Lambda$ +c.c.. The data were read from figure 2 in the paper, which is not background subtracted but has very small ($\sim1\%$) backgrounds.

Source code:BESII_2004_I650570.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> p K- Lambdabar class BESII_2004_I650570 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2004_I650570);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 443);
  declare(ufs, "UFS");
  DecayedParticles psi(ufs);
  psi.addStable(PID::PI0);
  psi.addStable(PID::K0S);
  psi.addStable(PID::LAMBDA);
  psi.addStable(-PID::LAMBDA);
  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) {
    int sign = 1;
    if (psi.modeMatches(ix, 3, mode))
      sign = 1;
    else if (psi.modeMatches(ix, 3, modeCC))
      sign = -1;
    else
      continue;
    const Particle pp = psi.decayProducts()[ix].at(sign * 2212)[0];
    const Particle lamBar = psi.decayProducts()[ix].at(-sign * 3122)[0];
    FourMomentum pL = pp.mom() + lamBar.mom();
    double mass = pL.mass();
    _h[0]->fill(mass / GeV);
    double delta = mass - pp.mass() - lamBar.mass();
    _h[1]->fill(delta / GeV);
    if (delta > .15) continue;
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        psi.decaying()[ix].mom().betaVec());
    FourMomentum pProton = boost.transform(pp.mom());
    pL = boost.transform(pL);
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pL.betaVec());
    pProton = boost2.transform(pProton);
    const double cosp = -pL.p3().unit().dot(pProton.p3().unit());
    _h[2]->fill(cosp);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[3];
const map<PdgId, unsigned int> mode = {{2212, 1}, {-3122, 1}, {-321, 1}};
const map<PdgId, unsigned int> modeCC = {{-2212, 1}, {3122, 1}, {321, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BESII_2004_I650570);

} ```