Rivet analyses

title: BABAR_2006_I714147

Helicity angle in $B^-\to D^0K^{*-}$

Experiment: BABAR (PEP-II)

Inspire ID: 714147

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 73 (2006) 111104

Beams: * *

Beam energies: ANY

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

Measurement of the Helicity angle in $B^-\to D^0K^{*-}$. The acceptance corrected data was read from Figure 2 in the paper and the background given subtracted.

Source code:BABAR_2006_I714147.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_2006_I714147 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I714147);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
  declare(ufs, "UFS");
  // hists
  book(_h, 1, 1, 1);
}

bool isKstar(int pid) const {
  return pid == 313 || pid == 323;
}

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

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

/// Perform the per-event analysis
void analyze(const Event& event) {
  UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& B : ufs.particles()) {
    if (B.children().size() != 2) continue;
    int sign = B.pid() / B.abspid();
    Particle D, Kstar;
    if (B.children()[0].pid() == -sign * 421 && isKstar(B.children()[1].abspid())) {
      D = B.children()[0];
      Kstar = B.children()[1];
    }
    else if (B.children()[1].pid() == -sign * 421 && isKstar(B.children()[0].abspid())) {
      D = B.children()[1];
      Kstar = B.children()[0];
    }
    else
      continue;
    // find Kstar decay products
    Particle pi;
    if (isK(Kstar.children()[0].abspid()) && isPi(Kstar.children()[1].abspid())) {
      pi = Kstar.children()[1];
    }
    else if (isK(Kstar.children()[1].abspid()) && isPi(Kstar.children()[0].abspid())) {
      pi = Kstar.children()[0];
    }
    else
      continue;
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
    FourMomentum pD = boost.transform(D.momentum());
    FourMomentum pKstar = boost.transform(Kstar.momentum());
    FourMomentum pPi = boost.transform(pi.momentum());
    // pion helicity angle
    Vector3 axisX = pD.p3().unit();
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    double cosPi = -axisX.dot(boostK.transform(pPi).p3().unit());
    _h->fill(cosPi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2006_I714147);

} ```