Rivet analyses

title: BELLE_2014_I1312626

Mass and angular distributions in $\bar{B}^0\to J/\psi K^-\pi^+$

Experiment: BELLE (KEKB)

Inspire ID: 1312626

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 90 (2014) 11, 112009

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, original Upsilon(4S)

Measurement of mass and angular distributions in $\bar{B}^0\to J/\psi K^-\pi^+$. The data were read from the plots in the paper and the backgrounds given subtracted.

Source code:BELLE_2014_I1312626.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Bbar0 -> J/[psi K- pi+ class BELLE_2014_I1312626 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2014_I1312626);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  DecayedParticles B0(ufs);
  B0.addStable(443);
  declare(B0, "B0");
  // histograms
  for (unsigned int ix = 0; ix < 7; ++ix) book(_h_mass[ix], 1, 1, 1 + ix);
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h_angle[ix], 2, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {-321, 1}, {443, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-211, 1}, {321, 1}, {443, 1}};
  DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
  for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
    int sign = 1;
    if (B0.decaying()[ix].pid() < 0 && B0.modeMatches(ix, 3, mode)) sign = 1;
    if (B0.decaying()[ix].pid() > 0 && B0.modeMatches(ix, 3, modeCC))
      sign = -1;
    else
      continue;
    const Particle& pip = B0.decayProducts()[ix].at(sign * 211)[0];
    const Particle& Km = B0.decayProducts()[ix].at(-sign * 321)[0];
    const Particle& JPsi = B0.decayProducts()[ix].at(443)[0];
    double mpiJ2 = (pip.momentum() + JPsi.momentum()).mass2();
    double mKpi2 = (pip.momentum() + Km.momentum()).mass2();
    if (mpiJ2 < 16.)
      _h_mass[0]->fill(mKpi2);
    else if (mpiJ2 < 19.)
      _h_mass[1]->fill(mKpi2);
    else
      _h_mass[2]->fill(mKpi2);
    if (mKpi2 < 1.2)
      _h_mass[3]->fill(mpiJ2);
    else if (mKpi2 < 2.05)
      _h_mass[4]->fill(mpiJ2);
    else if (mKpi2 < 3.2)
      _h_mass[5]->fill(mpiJ2);
    else
      _h_mass[6]->fill(mpiJ2);
    // mass cuts for angular variables
    if (mKpi2 < 1.2 || mpiJ2 < 16. || mpiJ2 > 19.) continue;
    // helicity angle find J.psi leptonic children
    if (JPsi.children().size() != 2) continue;
    if (JPsi.children()[0].pid() != -JPsi.children()[1].pid()) continue;
    if (JPsi.children()[0].abspid() != PID::EMINUS && JPsi.children()[0].abspid() != PID::MUON) continue;
    Particle lm = JPsi.children()[0];
    Particle lp = JPsi.children()[1];
    if (lm.pid() < 0) swap(lm, lp);
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        B0.decaying()[ix].momentum().betaVec());
    FourMomentum ppsi = boost1.transform(JPsi.momentum());
    Vector3 axis1 = -ppsi.p3().unit();
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppsi.betaVec());
    FourMomentum plp = boost2.transform(boost1.transform(lp.momentum()));
    double cL = plp.p3().unit().dot(axis1);
    _h_angle[0]->fill(cL);
    Vector3 LTrans = plp.p3() - cL * plp.p3().mod() * axis1;
    FourMomentum pKpi = boost1.transform(pip.momentum() + Km.momentum());
    LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pKpi.betaVec());
    FourMomentum ppi = boost3.transform(boost1.transform(pip.momentum()));
    double cPi = ppi.p3().unit().dot(axis1);
    Vector3 PTrans = ppi.p3() - cPi * ppi.p3().mod() * axis1;
    double phi = atan2(LTrans.cross(PTrans).dot(axis1), LTrans.dot(PTrans));
    _h_angle[1]->fill(phi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 7; ++ix) normalize(_h_mass[ix], 1., false);
  for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h_angle[ix], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass[7], _h_angle[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2014_I1312626);

} ```