Rivet analyses

title: BABAR_2011_I920989

Helicity angles in the decay $B^0\to D^{*0}\omega$

Experiment: BABAR (PEP-II)

Inspire ID: 920989

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 84 (2011) 112007,

Beams: * *

Beam energies: ANY

Run details: - Any process producing Bbar0, originally Upsilon(4S) decay

Measurement of the helicity angles in the decay $B^0\to D^{*0}\omega$. The data were read from the plots in the paper andmay not have been corrected.

Source code:BABAR_2011_I920989.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> D*0 omega class BABAR_2011_I920989 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2011_I920989);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  // histos
  for (unsigned int ix = 0; ix < 4; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1, 1 + ix, 1 + iy);
}

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) {
  for (const Particle& B0 : apply<UnstableParticles>(event, "UFS").particles()) {
    if (B0.children().size() != 2) continue;
    Particle Dstar, omega;
    if (B0.children()[0].abspid() == 423 && B0.children()[1].pid() == 223) {
      Dstar = B0.children()[0];
      omega = B0.children()[1];
    }
    else if (B0.children()[1].abspid() == 423 && B0.children()[0].pid() == 223) {
      Dstar = B0.children()[1];
      omega = B0.children()[0];
    }
    else
      continue;
    // check the no of decay products
    if (Dstar.children().size() != 2 || omega.children().size() != 3) continue;
    // find the children of the D* meson
    Particle D0;
    if (Dstar.children()[0].pid() == 111 && Dstar.children()[1].abspid() == 421)
      D0 = Dstar.children()[1];
    else if (Dstar.children()[1].pid() == 111 && Dstar.children()[0].abspid() == 421)
      D0 = Dstar.children()[0];
    else
      continue;
    // 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;
    // boost to B rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(B0.momentum().betaVec());
    FourMomentum pDstar = boost1.transform(Dstar.momentum());
    FourMomentum pD0 = boost1.transform(D0.momentum());
    FourMomentum pomega = boost1.transform(omega.momentum());
    FourMomentum pPip = boost1.transform(pip[0].momentum());
    FourMomentum pPim = boost1.transform(pim[0].momentum());
    // boost to D* frame
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
    pD0 = boost2.transform(pD0);
    double c1 = pD0.p3().unit().dot(pDstar.p3().unit());
    // boost to omega frame
    LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pomega.betaVec());
    pPip = boost3.transform(pPip);
    pPim = boost3.transform(pPim);
    Vector3 axisOmega = pPip.p3().cross(pPim.p3()).unit();
    double c2 = pomega.p3().unit().dot(axisOmega);
    for (unsigned int ix = 0; ix < 4; ++ix) {
      _h[ix][0]->fill(c1);
      _h[ix][1]->fill(c2);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 4; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) normalize(_h[ix][iy], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[4][2];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2011_I920989);

} ```