Rivet analyses

title: BABAR_2005_I664717

Helicity angles in $B^+\to\omega\rho^+$

Experiment: BABAR (PEP-II)

Inspire ID: 664717

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 71 (2005) 031103

Beams: * *

Beam energies: ANY

Run details: - Any process producing B mesons, originally Upsilon(4S) decays

Measurement of the $\rho$ and $\omega$ helicity angles in the decay $B^+\to\omega\rho^+$. The data for the background subtracted helicity angles were read from Figure 3 in the paper.

Source code:BABAR_2005_I664717.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B+ -> omega rho+ class BABAR_2005_I664717 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2005_I664717);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
  declare(ufs, "UFS");
  DecayedParticles BP(ufs);
  BP.addStable(213);
  BP.addStable(-213);
  BP.addStable(223);
  declare(BP, "BP");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
}

void findChildren(const Particle& p,
                  Particles& pim,
                  Particles& pip,
                  Particles& pi0,
                  unsigned int& ncount) {
  for (const Particle& child : p.children()) {
    if (child.pid() == PID::PIPLUS) {
      pip.push_back(child);
      ncount += 1;
    }
    else if (child.pid() == PID::PIMINUS) {
      pim.push_back(child);
      ncount += 1;
    }
    else if (child.pid() == PID::PI0) {
      pi0.push_back(child);
      ncount += 1;
    }
    else if (child.children().empty()) {
      ncount += 1;
    }
    else
      findChildren(child, pim, pip, pi0, ncount);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{223, 1}, {213, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{223, 1}, {-213, 1}};
  DecayedParticles BP = apply<DecayedParticles>(event, "BP");
  // loop over particles
  for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
    if (BP.modeMatches(ix, 2, mode) || BP.modeMatches(ix, 2, modeCC)) {
      const Particle& omega = BP.decayProducts()[ix].at(223)[0];
      // children of the omega
      unsigned int ncount = 0;
      Particles pip, pim, pi0;
      findChildren(omega, pim, pip, pi0, ncount);
      if (ncount != 3 || !(pim.size() == 1 && pip.size() == 1 && pi0.size() == 1)) continue;
      // rho decay
      int sign = BP.decaying()[ix].pid() / BP.decaying()[ix].abspid();
      const Particle& rho = BP.decayProducts()[ix].at(sign * 213)[0];
      if (rho.children().size() != 2) continue;
      Particle pi;
      if (rho.children()[0].pid() == sign * 211 && rho.children()[1].pid() == 111)
        pi = rho.children()[0];
      else if (rho.children()[1].pid() == sign * 211 && rho.children()[0].pid() == 111)
        pi = rho.children()[1];
      else
        continue;
      // boosts
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
          BP.decaying()[ix].momentum().betaVec());
      FourMomentum pomega = boost1.transform(omega.momentum());
      FourMomentum prho = boost1.transform(rho.momentum());
      FourMomentum pPip = boost1.transform(pip[0].momentum());
      FourMomentum pPim = boost1.transform(pim[0].momentum());
      FourMomentum pPi = boost1.transform(pi.momentum());
      // boost to omega frame
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pomega.betaVec());
      pPip = boost2.transform(pPip);
      pPim = boost2.transform(pPim);
      Vector3 axisOmega = pPip.p3().cross(pPim.p3()).unit();
      // helicity angle
      _h[0]->fill(abs(pomega.p3().unit().dot(axisOmega)));
      // boost to rho rest frame
      LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(prho.betaVec());
      pPi = boost3.transform(pPi);
      _h[1]->fill(prho.p3().unit().dot(pPi.p3().unit()));
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2005_I664717);

} ```