Rivet analyses

title: BELLE_2017_I1610301

$\Upsilon(2,3,4S)\to\Upsilon(1S)\pi^+\pi^-$ and $\Upsilon(4S)\to\Upsilon(2S)\pi^+\pi^-$

Experiment: BELLE (KEKB)

Inspire ID: 1610301

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 96 (2017) 5, 052005

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(2,3,4S), original e+e-

Measurement of the $\pi^+\pi^-$ mass Spectrum and pion helicity angle in $\Upsilon(2,3,4S)\to\Upsilon(1S)\pi^+\pi^-$ and $\Upsilon(4S)\to\Upsilon(2S)\pi^+\pi^-$ decays by the BELLE collaboration.

Source code:BELLE_2017_I1610301.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Upsilon -> Upsilon pi+pi- class BELLE_2017_I1610301 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1610301);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  for (unsigned int ix = 0; ix < 4; ++ix) {
    book(_h_mpipi[ix], 1, 1, ix + 1);
    book(_h_ctheta[ix], 2, 1, ix + 1);
  }
}

void findDecayProducts(const Particle& mother,
                       unsigned int& nstable,
                       Particles& pip,
                       Particles& pim,
                       Particles& pi0,
                       Particles& onium) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (id == PID::PIMINUS) {
      pim.push_back(p);
      ++nstable;
    }
    else if (id == PID::PIPLUS) {
      pip.push_back(p);
      ++nstable;
    }
    else if (id == PID::PI0) {
      pi0.push_back(p);
      ++nstable;
    }
    else if (abs(id) % 1000 == 443 || abs(id) % 1000 == 553) {
      onium.push_back(p);
      ++nstable;
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, nstable, pip, pim, pi0, onium);
    }
    else
      ++nstable;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& ups :
       apply<UnstableParticles>(event, "UFS")
           .particles(Cuts::pid == 100553 or Cuts::pid == 200553 or Cuts::pid == 300553)) {
    unsigned int nstable(0);
    Particles pip, pim, pi0, onium;
    findDecayProducts(ups, nstable, pip, pim, pi0, onium);
    // pions and no of products
    if (pip.size() != 1 || pim.size() != 1 || nstable != 3) continue;
    // check for onium
    if (onium.size() != 1) continue;
    if (!(onium[0].pid() == 553 || (ups.pid() == 300553 && onium[0].pid() == 100553))) continue;
    FourMomentum q = pip[0].momentum() + pim[0].momentum();
    // boost particles to upsilon rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    FourMomentum ppi = boost1.transform(pip[0].momentum());
    FourMomentum pUps = boost1.transform(onium[0].momentum());
    q = boost1.transform(q);
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(q.betaVec());
    ppi = boost2.transform(ppi);
    pUps = boost2.transform(pUps);
    double ctheta = ppi.p3().unit().dot(pUps.p3().unit());
    if (ups.pid() == 100553) {
      _h_mpipi[0]->fill(q.mass());
      _h_ctheta[0]->fill(ctheta);
    }
    else if (ups.pid() == 200553) {
      _h_mpipi[1]->fill(q.mass());
      _h_ctheta[1]->fill(ctheta);
    }
    else if (ups.pid() == 300553) {
      if (onium[0].pid() == 553) {
        _h_mpipi[2]->fill(q.mass());
        _h_ctheta[2]->fill(ctheta);
      }
      else {
        _h_mpipi[3]->fill(q.mass());
        _h_ctheta[3]->fill(ctheta);
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 4; ++ix) {
    normalize(_h_mpipi[ix]);
    normalize(_h_ctheta[ix]);
  }
}

///@}


/// @name Histograms
///@{
Histo1DPtr _h_mpipi[4];
Histo1DPtr _h_ctheta[4];
///@}

};

RIVET_DECLARE_PLUGIN(BELLE_2017_I1610301);

} ```