Rivet analyses

title: BABAR_2004_I626518

Helicity angles and polarization in $B^-\to D^{0}K^{-}$

Experiment: BABAR (PEP-II)

Inspire ID: 626518

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 92 (2004) 141801

Beams: * *

Beam energies: ANY

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

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

Source code:BABAR_2004_I626518.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B- -> D0 K- class BABAR_2004_I626518 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I626518);


/// @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(423);
  BP.addStable(-423);
  BP.addStable(323);
  BP.addStable(-323);
  declare(BP, "BP");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 2, 1 + ix, 1 + iy);
  for (unsigned int ix = 0; ix < 2; ++ix) book(_p[ix], "TMP/p_" + toString(ix + 1));
}

bool isK(int id) {
  return id == 321 || id == 311 || id == 310 || id == 130;
}

bool isPi(int id) {
  return id == 211 || id == 111;
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{-423, 1}, {323, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{423, 1}, {-323, 1}};
  DecayedParticles BP = apply<DecayedParticles>(event, "BP");
  // loop over particles
  for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
    int sign = 1;
    if (BP.decaying()[ix].pid() > 0 && BP.modeMatches(ix, 2, mode))
      sign = 1.;
    else if (BP.decaying()[ix].pid() < 0 && BP.modeMatches(ix, 2, modeCC))
      sign = -1.;
    else
      continue;
    // find D* decay products
    const Particle& Dstar = BP.decayProducts()[ix].at(-sign * 423)[0];
    if (Dstar.children().size() != 2) continue;
    Particle D0;
    unsigned int imode = 0;
    if (Dstar.children()[0].pid() == 111 && Dstar.children()[1].pid() == -sign * 421) {
      D0 = Dstar.children()[1];
      imode = 0;
    }
    else if (Dstar.children()[1].pid() == 111 && Dstar.children()[0].pid() == -sign * 421) {
      imode = 0;
      D0 = Dstar.children()[0];
    }
    else if (Dstar.children()[0].pid() == 22 && Dstar.children()[1].pid() == -sign * 421) {
      D0 = Dstar.children()[1];
      imode = 1;
    }
    else if (Dstar.children()[1].pid() == 22 && Dstar.children()[0].pid() == -sign * 421) {
      imode = 1;
      D0 = Dstar.children()[0];
    }
    else
      continue;
    // K* decay products
    const Particle& Kstar = BP.decayProducts()[ix].at(sign * 323)[0];
    if (Kstar.children().size() != 2) continue;
    Particle KK;
    if (isK(Kstar.children()[0].abspid()) && isPi(Kstar.children()[1].abspid()))
      KK = Kstar.children()[0];
    else if (isK(Kstar.children()[1].abspid()) && isPi(Kstar.children()[0].abspid()))
      KK = Kstar.children()[1];
    else
      continue;
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        BP.decaying()[ix].momentum().betaVec());
    FourMomentum pKstar = boost.transform(Kstar.momentum());
    FourMomentum pDstar = boost.transform(Dstar.momentum());
    FourMomentum pK = boost.transform(KK.momentum());
    FourMomentum pD = boost.transform(D0.momentum());
    const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
    pD = boost2.transform(pD);
    double cD = pD.p3().unit().dot(pDstar.p3().unit());
    const LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    pK = boost3.transform(pK);
    double cK = pK.p3().unit().dot(pKstar.p3().unit());
    if (imode == 0) {
      _p[0]->fill(-0.5 * (1 - 5 * sqr(cK)));
      _p[1]->fill();
    }
    _h[0][imode]->fill(cD);
    _h[1][imode]->fill(cK);
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2004_I626518);

} ```