Rivet analyses

title: CLEOII_1998_I467642

$\Upsilon(2S)\to\Upsilon(1S)\pi^+\pi^-$

Experiment: CLEOII (CUSB)

Inspire ID: 467642

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D58 (1998) 052004

Beams: * *

Beam energies: ANY

Run details: - In princple any process producing Upsilon(2S), but e+e- -> Upsilon(2S) needs for some dists

Measurement of the $\pi^+\pi^-$ mass Spectrum and other distributions in $\Upsilon(2S)\to\Upsilon(1S)\pi^+\pi^-$ decays.

Source code:CLEOII_1998_I467642.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Upsilon(2S) -> Upsilon(1S) pi+pi- class CLEOII_1998_I467642 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1998_I467642);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  book(_h_charged_ex, 1, 1, 1);
  book(_h_charged_inc, 2, 1, 1);
  book(_h_neutral_ex, 3, 1, 1);
  book(_h_lept_ctheta, 4, 1, 1);
  book(_h_lept_phi, 4, 1, 2);
  book(_h_piStar_ctheta, 5, 1, 1);
  book(_h_piStar_phi, 5, 1, 2);
  book(_h_pi_ctheta, 6, 1, 1);
  book(_h_pi_phi, 6, 1, 2);
}

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;
  }
}

void findLeptons(const Particle& mother, unsigned int& nstable, Particles& lp, Particles& lm) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (id == 11 || id == 13) {
      lm.push_back(p);
      ++nstable;
    }
    else if (id == -11 || id == -13) {
      lp.push_back(p);
      ++nstable;
    }
    else if (!p.children().empty()) {
      findLeptons(p, nstable, lp, lm);
    }
    else
      ++nstable;
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // loop over unstable particles
  for (const Particle& ups : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == 100553)) {
    unsigned int nstable(0);
    Particles pip, pim, pi0, onium;
    findDecayProducts(ups, nstable, pip, pim, pi0, onium);
    // check for onium
    if (onium.size() != 1 || onium[0].pid() != 553 || nstable != 3) continue;
    //pi+pi-
    if (pip.size() == 1 && pim.size() == 1) {
      FourMomentum q = pip[0].momentum() + pim[0].momentum();
      _h_charged_ex->fill(q.mass() / GeV);
      _h_charged_inc->fill(q.mass() / GeV);
      // leptons from Upsilon(1S) decay
      nstable = 0;
      Particles lp, lm;
      findLeptons(onium[0], nstable, lp, lm);
      if (nstable == 2 && lp.size() == 1 && lm.size() == 1) {
        _h_lept_ctheta->fill(cos(lp[0].momentum().polarAngle()));
        _h_lept_phi->fill(lp[0].momentum().azimuthalAngle());
      }
      // pions in rest frame
      LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(q.betaVec());
      FourMomentum ppi = boost.transform(pip[0].momentum());
      Vector3 axis1 = q.p3().unit();
      Vector3 axis2 = Vector3(0., 0., 1.).cross(axis1).unit();
      Vector3 axis3 = axis1.cross(axis2).unit();
      _h_piStar_ctheta->fill(axis1.dot(ppi.p3().unit()));
      double phi = atan2(axis3.dot(ppi.p3().unit()), axis2.dot(ppi.p3().unit()));
      if (phi < 0.) phi += 2. * M_PI;
      _h_piStar_phi->fill(phi);
      // pions in lab frame
      _h_pi_ctheta->fill(cos(q.polarAngle()));
      _h_pi_phi->fill(q.azimuthalAngle());
    }
    // 2pi0
    else if (pi0.size() == 2) {
      FourMomentum q = pi0[0].momentum() + pi0[1].momentum();
      _h_neutral_ex->fill(q.mass() / GeV);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_charged_ex);
  normalize(_h_charged_inc);
  normalize(_h_neutral_ex);
  normalize(_h_lept_ctheta);
  normalize(_h_lept_phi);
  normalize(_h_piStar_ctheta);
  normalize(_h_piStar_phi);
  normalize(_h_pi_ctheta);
  normalize(_h_pi_phi);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_charged_ex, _h_charged_inc, _h_neutral_ex;
Histo1DPtr _h_lept_ctheta, _h_lept_phi, _h_piStar_ctheta, _h_piStar_phi, _h_pi_ctheta, _h_pi_phi;
/// @}

};

RIVET_DECLARE_PLUGIN(CLEOII_1998_I467642);

} ```