Rivet analyses

title: BABAR_2003_I613283

Helicity angles and Polarization in $B^0\to D^{+}_sD^{-}$

Experiment: BABAR (PEP-II)

Inspire ID: 613283

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 67 (2003) 092003

Beams: * *

Beam energies: ANY

Run details: - Any proces producing B0 mesons, originally Upsilon(4S) decays

Measurement of the helicity angles and polarization in $B^0\to D^{+}_sD^{-}$. The polarization was given in the paper and the background subtracted data for the helicity angles was extracted from figure 2 in the paper.

Source code:BABAR_2003_I613283.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> Ds D class BABAR_2003_I613283 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2003_I613283);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  DecayedParticles B0(ufs);
  B0.addStable(413);
  B0.addStable(-413);
  B0.addStable(433);
  B0.addStable(-433);
  declare(B0, "B0");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 2, 1 + ix, 1);
  for (unsigned int ix = 0; ix < 2; ++ix) book(_p[ix], "TMP/p_" + toString(ix + 1));
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{433, 1}, {-413, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-433, 1}, {413, 1}};
  DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
  // loop over particles
  for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
    int sign = 1;
    if (B0.decaying()[ix].pid() > 0 && B0.modeMatches(ix, 2, mode))
      sign = 1.;
    else if (B0.decaying()[ix].pid() < 0 && B0.modeMatches(ix, 2, modeCC))
      sign = -1.;
    else
      continue;
    // find D* decay products
    const Particle& Dstar = B0.decayProducts()[ix].at(-sign * 413)[0];
    if (Dstar.children().size() != 2) continue;
    Particle pim;
    if (Dstar.children()[0].pid() == -sign * 211 && Dstar.children()[1].pid() == -sign * 421) {
      pim = Dstar.children()[0];
    }
    else if (Dstar.children()[1].pid() == -sign * 211 && Dstar.children()[0].pid() == -sign * 421) {
      pim = Dstar.children()[1];
    }
    else
      continue;
    // find Ds* decay products
    const Particle& DSstar = B0.decayProducts()[ix].at(sign * 433)[0];
    Particle gamma;
    if (DSstar.children()[0].pid() == 22 && DSstar.children()[1].pid() == sign * 431) {
      gamma = DSstar.children()[0];
    }
    else if (DSstar.children()[1].pid() == 22 && DSstar.children()[0].pid() == sign * 431) {
      gamma = DSstar.children()[1];
    }
    else
      continue;
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        B0.decaying()[ix].momentum().betaVec());
    FourMomentum pDSstar = boost.transform(DSstar.momentum());
    FourMomentum pDstar = boost.transform(Dstar.momentum());
    FourMomentum pGamma = boost.transform(gamma.momentum());
    FourMomentum pPim = boost.transform(pim.momentum());
    const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
    pPim = boost2.transform(pPim);
    double cPi = pPim.p3().unit().dot(pDSstar.p3().unit());
    const LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pDSstar.betaVec());
    pGamma = boost3.transform(pGamma);
    double cGamma = pGamma.p3().unit().dot(pDstar.p3().unit());
    _p[0]->fill(-100. * (1. - 5. * sqr(cPi)) / 2.);
    _p[1]->fill();
    _h[0]->fill(cPi);
    _h[1]->fill(cGamma);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix], 1., false);
  Estimate0DPtr tmp;
  book(tmp, 1, 1, 1);
  divide(*_p[0], *_p[1], tmp);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2003_I613283);

} ```